{"id":1513,"date":"2025-10-29T10:10:28","date_gmt":"2025-10-29T17:10:28","guid":{"rendered":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/?page_id=1513"},"modified":"2026-03-12T08:59:26","modified_gmt":"2026-03-12T15:59:26","slug":"chapter-19-weeds-and-weed-management","status":"publish","type":"page","link":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/chapter-19-weeds-and-weed-management\/","title":{"rendered":"Chapter 19: Weeds and Weed Management"},"content":{"rendered":"<div class=\"wsu-hero wsu-width--full wsu-pattern--wsu-light-radial-left  wsu-hero--style-boxed \">\n\t<div class=\"wsu-hero__background\">\n\t\t<div class=\"wsu-image-frame wsu-image-frame--fill\">\n\t<img decoding=\"async\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/09\/AdobeStock_76248803-1.jpg\"\n\t\tsrcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/09\/AdobeStock_76248803-1.jpg 1350w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/09\/AdobeStock_76248803-1.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/09\/AdobeStock_76248803-1.jpg 1024w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/09\/AdobeStock_76248803-1.jpg 768w\"\n\t\tsizes=\"(max-width: 1350px) 100vw, 1350px\"\n\t\talt=\"Yellow dandelion flowers in green grass in the spring.\"\n\t\tstyle=\"object-position: 73% 79%\"\n\t\t\/>\n<\/div>\n\t<\/div>\n\t<div class=\"wsu-hero__overlay\">\n\t<\/div>\n\t<div class=\"wsu-hero__content-wrapper\">\n\t\t<div class=\"wsu-hero__inner-content-wrapper\">\n\t\t\t\t\t\t<div class=\"wsu-hero__title-wrapper\">\n\t\t\t\t<h1 class=\"wsu-hero__title\">Weeds and Weed<br>Management<\/h1>\t\t\t\t<div class=\"wsu-hero__caption\">Chapter 19<\/div>\t\t\t\t\t\t\t<\/div>\n\t\t\t\t\t\t<div class=\"wsu-hero__content\">\n\t\t\t<\/div>\n\t\t<\/div>\n\t<\/div>\n<\/div>\n\n\n\n<p class=\"wsu-max-width--hero wsu-spacing-after--xsmall\"><strong>Tim Miller<\/strong>, Extension Weed Scientist, Washington State University<\/p>\n\n\n\n<p class=\"wsu-font-size--medium wsu-spacing-after--xsmall\"><em>All photos in this chapter are the work of the author.<\/em><\/p>\n\n\n\n<div style=\"height:10px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\" \/>\n\n\n<div class=\"wsu-row wsu-row--sidebar-right\" >\r\n    \n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<h2 class=\"wp-block-heading wsu-font-size--xlarge wsu-heading--style-marked wsu-spacing-after--xxmedium\" id=\"learning-objectives\">Learning Objectives<\/h2>\n\n\n\n<ul>\n<li>Know the attributes that result in a plant being considered a weed.<\/li>\n\n\n\n<li>Understand the biology of weed growth, development, and spread.<\/li>\n\n\n\n<li>Know accepted methods of weed management for home yards and gardens.<\/li>\n<\/ul>\n\n<\/div>\r\n\n\n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<h2 class=\"wp-block-heading\">Topics Covered<\/h2>\n\n\n\n<ul class=\"wsu-menu--style-sidebar\">\n<li><a href=\"#ch19-introduction\" data-type=\"internal\" data-id=\"#ch19-introduction\">Introduction<\/a><\/li>\n\n\n\n<li><a href=\"#ch19-weed-attributes\" data-type=\"internal\" data-id=\"#ch19-weed-attributes\">Weed Attributes<\/a><\/li>\n\n\n\n<li><a href=\"#ch19-weed-identification\" data-type=\"internal\" data-id=\"#ch19-weed-identification\">Weed Identification<\/a><\/li>\n\n\n\n<li><a href=\"#ch19-weed-management\" data-type=\"internal\" data-id=\"#ch19-weed-management\">Weed Management<\/a><\/li>\n\n\n\n<li><a href=\"#ch19-resources-herbicides\" data-type=\"internal\" data-id=\"#ch19-resources-herbicides\">Resources on Herbicides<\/a><\/li>\n\n\n\n<li><a href=\"#ch19-further-reading\" data-type=\"internal\" data-id=\"#ch19-further-reading\">Further Reading<\/a><\/li>\n<\/ul>\n\n<\/div>\r\n\n<\/div>\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\" \/>\n\n\n<div class=\"wsu-callout wsu-border--color-vineyard wsu-callout--style-basic wsu-color-background--gray-5 wsu-border--add-left wsu-align-item--center wsu-spacing-after--large wsu-spacing-before--large wsu-max-width--xxmedium\" >\r\n        \n\n<p class=\"has-text-align-center wsu-font-size--medium\">\u201cBoth thorns and thistles the ground shall<br>bring forth for you.\u201d Genesis 3:18.<\/p>\n\n\n\n<p class=\"has-text-align-center wsu-font-size--medium\">\u201cMany things grow in the garden that were never sowed there.\u201d<br> Thomas Fuller, <em>Gnomologia<\/em>, 1732.<\/p>\n\n<\/div>\r\n\n\n\n<h2 class=\"wp-block-heading  wsu-heading--style-marked\" id=\"ch19-introduction\">Introduction<\/h2>\n\n\n\n<p>Few would argue that weeds (such as the \u201cthorns and thistles\u201d above) have been a plague for humanity for a long time! In fact, ever since the advent of agriculture some 10,000 years ago, weeds have fought with, and often defeated, our treasured crop and landscape plants. This chapter will discuss where weeds come from, why they are so successful at what they do, and what gardeners can do about them.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Definition<\/em><\/h3>\n\n\n\n<p>Weeds are often defined as those plants that are growing where we don\u2019t want them to grow. Yet, this \u201cplant out of place\u201d definition doesn\u2019t tell the whole story. While it is true that a volunteer squash plant growing in your pea patch may very well be a \u201cweed\u201d because you would prefer it not grow there, it is also true that this situation doesn\u2019t take into account the fact that squash plants are not particularly \u201cweedy\u201d\u2014that is, squash plants are not especially competitive, they do not tend to spread to new sites, nor do they tend to infest the same soil year after frustrating year. So a better definition of a weed would cite the biological attributes of the plant\u2014those that make the plant weedy\u2014in addition to the way it is disagreeable to the gardener. A textbook weed would therefore be \u201ca plant that is competitive, persistent, invasive, and interferes with human activities and is therefore undesirable.\u201d<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Weed Problems<\/em><\/h3>\n\n\n\n<p>Weeds cause multiple problems for gardeners, farmers, and land managers. Weeds compete with the plants we are trying to grow in the landscape or as vegetables and harbor plant-harming diseases and insects. Weeds also may attract and hide rodents that feed on our desirable plants. Weeds can reduce the aesthetic value of landscapes and the monetary value of real estate, and can negatively affect native plant and animal communities in forests, rangelands, and streams. On roadsides, weeds obstruct sight lines and can shorten the life span of asphalt shoulders. In waterways, weeds can interfere with water drainage patterns, increase sedimentation, and increase the likelihood of streambank failure in times of high stream flow. Weeds can create a fire hazard in suburban forested locations, along rail and roadways, and in electrical substations. Finally, many weeds often present direct allergy or toxicity hazards for humans and livestock through skin contact, inhalation, or ingestion.<\/p>\n\n\n\n<p>This is not to say that weeds are wholly without positive attributes. As Ralph Waldo Emerson observed, a weed is \u201ca plant whose virtues have not yet been discovered.\u201d St. Johnswort (<em>Hypericum perforatum<\/em>), for example (Figure 1), was once simply a bad weed in rangelands throughout the West but is now prized as an herbal antidepressant. Sometimes a weed\u2019s virtues are readily apparent. Many weed species are a delight to the eye, nose, or taste buds and sometimes are planted purposefully for those uses. One need look no further than Scotch broom (<em>Cytisus scoparius<\/em>) (Figure 2) or purple loosestrife to find a beautiful ornamental that soon becomes too much of a good thing. A similar Jekyll-and-Hyde theme applies to plants such as white clover (<em>Trifolium repens<\/em>), which can be a good addition to pasture vegetation but also frequently infests lawns and attracts stinging insects to where barefoot children like to play.<\/p>\n\n\n<div class=\"wsu-row wsu-spacing-before--large wsu-spacing-after--large wsu-row--halves\" >\r\n    \n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01A.jpg\" alt=\"St. Johnswort leaves with shiny beetle perched atop.\" class=\"wp-image-3376\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01A.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01A-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 1. St. Johnswort (<em>Hypericum perforatum<\/em>) leaves with biological control beetle (<em>Chrysolina<\/em> spp.) present (left). St. Johnswort with flowers (right).<\/figcaption><\/figure>\n\n<\/div>\r\n\n\n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01B.jpg\" alt=\"Close-up of yellow St. Johnswort flowers.\" class=\"wp-image-3377\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01B.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01B-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_01B-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><\/figure>\n\n<\/div>\r\n\n<\/div>\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_02-1.jpg\" alt=\"Close-up of yellow Scotch broom branch and flowers.\" class=\"wp-image-3378\" width=\"450\" height=\"300\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_02-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_02-1-300x200.jpg 300w\" sizes=\"(max-width: 450px) 100vw, 450px\" \/><figcaption class=\"wp-element-caption\">Figure 2. Scotch broom (<em>Cytisus scoparius<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<h3 class=\"wp-block-heading\"><em>Weed Sources<\/em><\/h3>\n\n\n\n<p>Most problem weeds in North America are native to foreign regions where many of our common agricultural crops had their beginnings: in Europe and Asia. This shouldn\u2019t be a surprise. After all, as crops such as wheat, barley, oat, pea, beet, cabbage, and many others were brought by early settlers to North America, seed contaminants such as wild oat (<em>Avena fatua<\/em>), common lambsquarters (<em>Chenopodium album<\/em>) (Figure 3), and shepherd\u2019s-purse (<em>Capsella bursa-pastoris<\/em>) almost certainly were carried along and introduced at the same time, albeit not on purpose. These weeds found the plowed fields where the new crops were planted very much to their liking and promptly made themselves at home.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_03-1.jpg\" alt=\"Top-down view of common lambsquarters.\" class=\"wp-image-3380\" width=\"450\" height=\"300\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_03-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_03-1-300x200.jpg 300w\" sizes=\"(max-width: 450px) 100vw, 450px\" \/><figcaption class=\"wp-element-caption\">Figure 3. Common lambsquarters (<em>Chenopodium album<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p>For the most part, weedy species are problems outside their homeland. This is not to say that these plants weren\u2019t weedy in their native lands, but there is a tendency for many species to be more aggressive in their new homes than where they came from. This is usually because plants in their homeland are generally surrounded by natural enemies\u2014diseases or insects that attack the plant and keep the population in check. Another factor may be that since certain plants evolved under more severe conditions in their homeland than in their new location, the new environment is more conducive to their growth and spread. Consider the case of Scotch broom, which competes well with other shrubs in its native environment and therefore is able to easily out-compete much of the native vegetation of western Washington. Sometimes these new plant species fill a previously empty niche in their introduced environment, such as was found and exploited by downy brome (cheatgrass; <em>Bromus tectorum<\/em>) throughout the Intermountain West. Or perhaps it was a combination of these reasons, giving plants like yellow starthistle (<em>Centaurea solstitialis<\/em>), kochia (<em>Bassia scoparia<\/em>), purple loosestrife (<em>Lythrum salicaria<\/em>), and garlic mustard (<em>Alliaria petiolata<\/em>) the opportunity to establish themselves and dominate their new surroundings.<\/p>\n\n\n\n<h2 class=\"wp-block-heading  wsu-heading--style-marked\" id=\"ch19-weed-attributes\">Weed Attributes<\/h2>\n\n\n\n<p>Although we may not always think in these terms when talking about plants, it is survival of the fittest in our lawns and gardens, and \u201cthe fittest\u201d plants are often weeds. You\u2019ll remember that we defined weeds as plants that are competitive, persistent, invasive, and interfere with what we want to do with the land. Let\u2019s examine these attributes separately and see why weeds are so good at what they do.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Weed Competition<\/em><\/h3>\n\n\n\n<p>Whenever two plants grow close enough to each other to interact, competition occurs. Plants compete with each other for four things: light, water, nutrients, and space. Often it is the first plant on the scene that enjoys a competitive advantage in gaining the lion\u2019s share of these four resources. Because most garden soil is chock-full of weed seeds, usually the first plant emerging from disturbed soil is a weed. This pioneer plant occupies physical space (1), rapidly produces a root system to gather water (2) and nutrients (3) from the soil before another plant can do the same, and grows a leaf canopy to harvest light energy (4) while shading out other, smaller plants. The bigger a weed gets, the better it is at competing against other vegetation, and the more of these four resources it acquires.<\/p>\n\n\n\n<p>Keep in mind also that the longer two plants grow together, the more intense the competition becomes. Because weeds frequently emerge before vegetable plants do, early-season competition from weeds can slow crop growth appreciably. In fact, early-season competition may permanently reduce the yield capacity of those vegetables even if those weeds are removed later. Research has shown that if weeds are controlled early in a cropping system, crop plants grow larger early in the season and become increasingly better able to compete with late-germinating weeds so yield loss can be avoided.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_04-1.jpg\" alt=\"Close-up of purple spotted knapweed flower.\" class=\"wp-image-3382\" width=\"300\" height=\"300\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_04-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_04-1-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_04-1-150x150.jpg 150w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><figcaption class=\"wp-element-caption\">Figure 4. Spotted knapweed (<em>Centaurea stoebe<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p>Weed density can also play a role in competition. Two common lambsquarters plants are more competitive with carrot than is one common lambsquarters plant. In another example, one published report showed that as few as three white mustard (<em>Sinapis alba<\/em>) plants per square foot can reduce green pea yield by 47%, and that situation is similar for other weed\/crop interactions. Given that the number of weeds in garden soil commonly exceeds 100 seedlings per square foot, it becomes clear that weed densities are almost always high enough to severely restrict crop productivity. Such reductions can be exacerbated if more than one species of weed is competing with our crop at the same time, since different weeds may compete with crops in different ways. It may be that one redroot pigweed (<em>Amaranthus retroflexus<\/em>) plant and one field pennycress (<em>Thlaspi arvense<\/em>) plant growing with one broccoli plant may be worse for the crop than two pigweeds or two pennycresses with the same broccoli plant.<\/p>\n\n\n<div class=\"wp-block-image wsu-spacing-after--large\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_05-1.jpg\" alt=\"Close-up of barnyardgrass against brown counter backdrop.\" class=\"wp-image-3387\" width=\"293\" height=\"440\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_05-1.jpg 400w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_05-1-200x300.jpg 200w\" sizes=\"(max-width: 293px) 100vw, 293px\" \/><figcaption class=\"wp-element-caption\">Figure 5. Barnyardgrass (<em>Echinochloa crus-galli<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p>Another way weeds outcompete other plants is through <em>allelopathy<\/em>. This is the production or accumulation of certain compounds in the leaves, stems, or roots of certain plants that, upon release into the soil, inhibit the growth of surrounding vegetation. Most of these allelopathic chemicals affect all the plants growing at a particular site. Saltcedar (<em>Tamarix<\/em> spp.), for example, exude excess salts on the surface of their leaves and this, over time, makes the underlying soil less suitable for new plant establishment, giving the established perennial an advantage against everything else that might challenge it. Other chemicals don\u2019t inhibit the growth of the plant species producing them but do slow the growth of most other plants, resulting in monotypic stands of single species. Spotted knapweed (<em>Centaurea stoebe<\/em>) (Figure 4) is one example of an allelopathic weed.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Weed Persistence<\/em><\/h3>\n\n\n\n<p class=\"wsu-spacing-after--large\">Once a weed has established itself or gone to seed in a garden, it seems we have that weed (or its progeny) to deal with every year afterwards. What makes weeds so persistent? First, they are difficult to kill. They tend to break off in our hands if we try to pull them, growing back from small pieces of root or crowns left in the soil. They also produce lots of seeds, averaging tens of thousands per plant compared to only several hundred seeds produced by most crop plants. See Table 1 for some weed seed comparisons.<\/p>\n\n\n<span id=\"tablepress-89-description\" class=\"tablepress-table-description tablepress-table-description-id-89\">Table 1. Approximate number of seeds produced per plant for some common PNW weed species.<\/span>\n\n<table id=\"tablepress-89\" class=\"tablepress tablepress-id-89\" aria-describedby=\"tablepress-89-description\">\n<thead>\n<tr class=\"row-1 odd\">\n\t<th class=\"column-1\">Weed Species<\/th><th class=\"column-2\">Seed Number<\/th>\n<\/tr>\n<\/thead>\n<tbody class=\"row-hover\">\n<tr class=\"row-2 even\">\n\t<td class=\"column-1\">Barnyardgrass <em>(Echinochloa crus-galli)<\/em><\/td><td class=\"column-2\">7,000<\/td>\n<\/tr>\n<tr class=\"row-3 odd\">\n\t<td class=\"column-1\">Shepherd\u2019s-purse <em>(Capsella bursa-pastoris)<\/em><\/td><td class=\"column-2\">38,500<\/td>\n<\/tr>\n<tr class=\"row-4 even\">\n\t<td class=\"column-1\">Curly dock <em>(Rumex crispus)<\/em><\/td><td class=\"column-2\">40,000<\/td>\n<\/tr>\n<tr class=\"row-5 odd\">\n\t<td class=\"column-1\">Common purslane <em>(Portulaca oleracea)<\/em><\/td><td class=\"column-2\">52,000<\/td>\n<\/tr>\n<tr class=\"row-6 even\">\n\t<td class=\"column-1\">Common lambsquarters <em>(Chenopodium album)<\/em><\/td><td class=\"column-2\">72,000<\/td>\n<\/tr>\n<tr class=\"row-7 odd\">\n\t<td class=\"column-1\">Redroot pigweed <em>(Amaranthus retroflexus)<\/em><\/td><td class=\"column-2\">117,000<\/td>\n<\/tr>\n<tr class=\"row-8 even\">\n\t<td class=\"column-1\">Black nightshade <em>(Solanum nigrum)<\/em><\/td><td class=\"column-2\">178,000<\/td>\n<\/tr>\n<tr class=\"row-9 odd\">\n\t<td class=\"column-1\">Russian-thistle <em>(tumbleweed;Salsola tragus)<\/em><\/td><td class=\"column-2\">200,000<\/td>\n<\/tr>\n<tr class=\"row-10 even\">\n\t<td class=\"column-1\">Palmer amaranth <em>(Amaranthus palmeri)<\/em><\/td><td class=\"column-2\">1,000,000<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<!-- #tablepress-89 from cache -->\n\n\n\n<p class=\"wsu-spacing-after--large wsu-font-size--xsmall\"><em>Source<\/em>: Data from Stevens (1932), Schreiber (1965), Dickerson and Sweet (1971), Chandler and Dale (1974), Muenscher (1955), Cavers and Harper (1964), Evans and Young (1974), Shaw et al. (1962), and Sosnoskie et al. (2014). Table from Ross and Lembi (1985).<\/p>\n\n\n<div class=\"wp-block-image wsu-spacing-before--xxmedium\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_06-1.jpg\" alt=\"Close-up of hairy nightshade\u2019s small white flowers and unopened globular seedpods.\" class=\"wp-image-3388\" width=\"304\" height=\"304\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_06-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_06-1-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_06-1-150x150.jpg 150w\" sizes=\"(max-width: 304px) 100vw, 304px\" \/><figcaption class=\"wp-element-caption\">Figure 6. Hairy nightshade (<em>Solanum physalifolium<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p class=\"wsu-spacing-after--default wsu-spacing-before--large\">Unlike crop seeds, weed seeds typically do not all germinate at the same time. Weed seeds tend to germinate only when conditions are right for establishment for that given species. So, weeds that like warm temperatures, such as barnyardgrass (<em>Echinochloa crus-galli<\/em>) (Figure 5) or hairy nightshade (<em>Solanum physalifolium<\/em>) (Figure 6), produce seeds that normally won\u2019t germinate until the days are long and soils are warm (late spring and summer). Conversely, seeds produced by shepherd\u2019s-purse tend to germinate in cooler soils when day lengths are less than 12 hours (fall and early spring). Most weed seeds also won\u2019t germinate unless they are exposed to some light, regardless of soil temperature. Such a germination response is important to prevent weed seeds from germinating when they are buried too deeply to allow their seedlings to emerge. It also allows weeds to respond quickly to disturbance of soil or vegetation which creates an empty space where the weed can thrive.<\/p>\n\n\n\n<p class=\"wsu-spacing-after--default\">Most weed species also produce seeds with a high level of dormancy, so that some weed seeds remain safely alive, but not germinating, even when conditions are right for germination (Table 2). These dormant seeds allow the species to persist even if a late frost kills all the early-germinating seedlings. This also helps weed seedlings avoid your attempts to kill off the population by careful removal of the first flush of seedlings in the springtime. Dormant seeds, or those nondormant seeds that are buried deeply in the soil, may survive for many years before they are brought to the surface by soil disturbance. Still, weed seeds are not immune to the ravages of time. Most weed seeds germinate or rot away within the first three or four years after they are produced, provided that conditions are adequate for germination. It is the last 0.5 to 1% of the total seed production that lies buried in soil for up to 40 years (or more!), waiting for their chance to sneak in a crop of fresh weed seeds when your guard is down. Of course, if only 0.5% of the perhaps 20,000 seeds that a single weed can produce in a single year survives for 25 years, we\u2019re still talking about 100 seeds\u2014not an inconsequential number of weed seedlings to deal with!<\/p>\n\n\n\n<p class=\"wsu-spacing-after--large\">Seeds aren\u2019t the only way weeds can beat you. As many plants do, weeds also reproduce vegetatively through creeping roots, rhizomes, stolons, bulbs, or tubers. These vegetative reproductive structures contain a lot of stored sugars and starch that provide a young plant with much more energy than is available from most seeds. New shoots arising from a tuber or rhizome fragment, then, can emerge from a greater soil depth than a shoot from a seed ever could. Such shoots also usually grow faster and capture space (and the light, water, and nutrients within that space) much more quickly than will a typical weed or crop seedling.<\/p>\n\n\n<span id=\"tablepress-90-description\" class=\"tablepress-table-description tablepress-table-description-id-90\">Table 2. Longevity of weed seeds buried in the soil.<\/span>\n\n<table id=\"tablepress-90\" class=\"tablepress tablepress-id-90\" aria-describedby=\"tablepress-90-description\">\n<thead>\n<tr class=\"row-1 odd\">\n\t<th class=\"column-1\">Weed Species<\/th><th class=\"column-2\">Years<sup>a<\/sup><\/th>\n<\/tr>\n<\/thead>\n<tbody class=\"row-hover\">\n<tr class=\"row-2 even\">\n\t<td class=\"column-1\">Quackgrass (<i>Elymus repens<\/i>)<\/td><td class=\"column-2\">1 to 6<\/td>\n<\/tr>\n<tr class=\"row-3 odd\">\n\t<td class=\"column-1\">Common milkweed (<i>Asclepias syriaca<\/i>)<\/td><td class=\"column-2\">3<\/td>\n<\/tr>\n<tr class=\"row-4 even\">\n\t<td class=\"column-1\">Wild oat (<i>Avena fatua<\/i>)<\/td><td class=\"column-2\">4 to 7<\/td>\n<\/tr>\n<tr class=\"row-5 odd\">\n\t<td class=\"column-1\">Common cocklebur (<i>Xanthium strumarium<\/i>)<\/td><td class=\"column-2\">16<\/td>\n<\/tr>\n<tr class=\"row-6 even\">\n\t<td class=\"column-1\">Foxtail (<i>Setaria spp.<\/i>)<\/td><td class=\"column-2\">20<\/td>\n<\/tr>\n<tr class=\"row-7 odd\">\n\t<td class=\"column-1\">Field bindweed (<i>Convolvulus arvensis<\/i>)<\/td><td class=\"column-2\">20+<\/td>\n<\/tr>\n<tr class=\"row-8 even\">\n\t<td class=\"column-1\">Canada thistle (<i>Cirsium arvense<\/i>)<\/td><td class=\"column-2\">21<\/td>\n<\/tr>\n<tr class=\"row-9 odd\">\n\t<td class=\"column-1\">Common lambsquarters (<i>Chenopodium album<\/i>)<\/td><td class=\"column-2\">40<\/td>\n<\/tr>\n<tr class=\"row-10 even\">\n\t<td class=\"column-1\">Redroot pigweed (<i>Amaranthus retroflexus<\/i>)<\/td><td class=\"column-2\">40<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<!-- #tablepress-90 from cache -->\n\n\n\n<p class=\"wsu-spacing-after--large wsu-font-size--xsmall wsu-max-width--xhero\"><em>Source<\/em>: Data from Holm et al. (1977), Klingman and Ashton (1982), Martin and Burnside (1980), and Salisbury and Ross (1978). Table from Ross and Lembi (1985).<br><sup>a<\/sup> Viability may be anywhere from 1 to 100% at the end of the year range.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_07-1.jpg\" alt=\"Catchweed bedstraw covered in very small hairs and bearing a few white flowers.\" class=\"wp-image-3399\" width=\"422\" height=\"281\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_07-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_07-1-300x200.jpg 300w\" sizes=\"(max-width: 422px) 100vw, 422px\" \/><figcaption class=\"wp-element-caption\">Figure 7. Catchweed bedstraw (<em>Galium aparine<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<h3 class=\"wp-block-heading\"><em>Weed Invasiveness<\/em><\/h3>\n\n\n\n<p class=\"wsu-spacing-after--large\">Weeds simply don\u2019t stay where they first grow. By hook or by crook, they constantly spread to new ground. They do this primarily by means of seeds, many of which are well-suited for movement after they are mature. Some seeds (or the fruits that bear them) are covered with hooks, spines, or awns which attach to fur or feathers or clothing (awns are the bristle-like growths on grass heads and seeds). Examples include common burdock (<em>Arctium minus<\/em>), houndstongue (<em>Cynoglossum officinale<\/em>), catchweed bedstraw (<em>Galium aparine<\/em>) (Figure 7), and hare barley (<em>Hordeum murinum<\/em>). Some seeds bear hairs or wings which allow them to blow with the wind; examples include dandelion (<em>Taraxacum officinale<\/em>) (Figure 8), Canada thistle (<em>Cirsium arvense<\/em>) (Figure 9), rush skeletonweed (<em>Chondrilla juncea<\/em>), and showy milkweed (<em>Asclepias speciosa<\/em>). Some are corky or hollow and extremely buoyant in water; one such example is broadleaf dock (<em>Rumex obtusifolius<\/em>) (Figure 10). Some are borne in tasty or colorful fruits that are consumed by animals and spread in their fecal material; examples include Himalaya blackberry (<em>Rubus armeniacus<\/em>), bittersweet nightshade (<em>Solanum dulcamara<\/em>) (Figure 11), and English ivy (<em>Hedera helix<\/em>). Such adaptations mean there will be no shortage of weed seeds in most yards and gardens waiting for their chance to sprout and establish in these new areas.<\/p>\n\n\n<div class=\"wsu-row wsu-spacing-before--large wsu-spacing-after--large wsu-row--halves\" >\r\n    \n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08B-1.jpg\" alt=\"Someone holds up a dandelion leaf and a common catsear leaf.\" class=\"wp-image-3411\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08B-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08B-1-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 8. Dandelion (<em>Taraxacum officinale<\/em>; left) and flowers (right).<\/figcaption><\/figure>\n\n<\/div>\r\n\n\n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08A-1.jpg\" alt=\"Someone holds up two yellow flowers that look very similar, except for increased symmetry and less dense flower petals in the right flower.\" class=\"wp-image-3410\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08A-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08A-1-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_08A-1-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><\/figure>\n\n<\/div>\r\n\n<\/div>\n\n\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped wp-block-gallery-1 is-layout-flex\">\n<figure class=\"wp-block-image size-large wsu-spacing-after--none\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3412\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09A-1.jpg\" alt=\"Prostrate Canada thistle rosettes.\" class=\"wp-image-3412\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09A-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09A-1-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large wsu-spacing-after--none\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3414\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09B-1.jpg\" alt=\"Close-up of cluster of pink Canada thistle flowers.\" class=\"wp-image-3414\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09B-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09B-1-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large wsu-spacing-after--none\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" data-id=\"3413\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09C-1.jpg\" alt=\"Close-up of cluster of Canada thistle buds, with one beginning to open, showing the pink flower tuft.\" class=\"wp-image-3413\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09C-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09C-1-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_09C-1-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><\/figure>\n<\/figure>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_10-1.jpg\" alt=\"Broadleaf dock with tall vertical stems sporting clusters of seeds and flowers.\" class=\"wp-image-3405\" width=\"325\" height=\"488\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_10-1.jpg 400w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_10-1-200x300.jpg 200w\" sizes=\"(max-width: 325px) 100vw, 325px\" \/><figcaption class=\"wp-element-caption\">Figure 10. Broadleaf dock (<em>Rumex obtusifolius<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p class=\"wsu-spacing-after--large wsu-font-size--xsmall\">Figure 9. Canada thistle (<em>Cirsium arvensis<\/em>) rosettes (top), flowerheads (middle), and seedheads (bottom).<\/p>\n\n\n\n<p>Weeds also spread vegetatively, not only by means of the reproductive structures mentioned above, but also by movement of the plants themselves. Mowers, vehicles, and cultivation equipment constantly dislodge and move plants from one place to another, often resulting in weed introductions into new areas. Animal bedding, bird seed, or hay bales may contain weed seed that either gets deposited on the ground or ingested or otherwise spread by the animal. People purposely introduce potential weed species for their beautiful foliage or sweet-smelling flowers but are unaware of their weedy nature. Sometimes these introductions are accidental, through purchase of containerized plants growing in infested potting soil, weed rhizomes entwined in bare root ornamentals, or weed seeds or stolons in contaminated mulch, beauty bark, compost, or topsoil.<\/p>\n\n\n\n<h2 class=\"wp-block-heading  wsu-heading--style-marked\" id=\"ch19-weed-identification\">Weed Identification<\/h2>\n\n\n\n<p>The best way to control any weed species is to hit it at its weakest point. Therefore, you must know something about the weed in question: its biology, its habits, its strategies for success. In a real sense, the first step toward effective weed management is to identify which weeds you have. Once you know you are looking at common chickweed (<em>Stellaria media<\/em>), for example, you know you are fighting a particular kind of weed with a certain life cycle and certain likes and dislikes. Often, weed identification can easily be accomplished by matching your unknown plant with photos published in reference books or websites, or by using software to identify weeds by their characteristics.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_11-1.jpg\" alt=\"Close-up of cluster of red bittersweet nightshade berries.\" class=\"wp-image-3415\" width=\"412\" height=\"274\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_11-1.jpg 434w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_11-1-300x200.jpg 300w\" sizes=\"(max-width: 412px) 100vw, 412px\" \/><figcaption class=\"wp-element-caption\">Figure 11. Bittersweet nightshade (Solanum dulcamara).<\/figcaption><\/figure><\/div>\n\n\n<p>The process of weed identification is easier if you know a little about the plant in the first place. Taxonomically, weeds (as with all other plants) are classified by what they look like: are they a monocot, dicot, or miscellaneous (moss, ferns, horsetails, etc.)? What plant family are they in, and what are the main family characteristics? Since common names can vary widely by their geographic distribution, knowing a weed\u2019s scientific name is necessary.<\/p>\n\n\n\n<p>Why is knowing family characteristics important? Consider that there are approximately 250,000 plant species in the world. Of these, only about 3% (8,000 species) of all plants are weedy in agriculture, while about 250 or 0.1% of the total are major problems in world agriculture. By knowing a few characteristics of an unidentified plant, we can often link a plant to its family\u2014often removing 90% or more of known plants from the list of possible plants in one fell swoop. For example, plants that bear flowers with four petals and six stamens often belong to the mustard family (Brassicaceae), while plants with square stems and opposite leaves often are in the mint family (Lamiaceae). Since it is much easier to compare an unknown weed with plants from a given family, as opposed to all the weeds in a particular book, plant identification can be accomplished more quickly and accurately.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_12-1.jpg\" alt=\"Common groundsel.\" class=\"wp-image-3420\" width=\"395\" height=\"395\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_12-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_12-1-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_12-1-150x150.jpg 150w\" sizes=\"(max-width: 395px) 100vw, 395px\" \/><figcaption class=\"wp-element-caption\">Figure 12. Common groundsel (<em>Senecio vulgaris<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<h3 class=\"wp-block-heading\"><em>Weed Life Cycles<\/em><\/h3>\n\n\n\n<p>Weeds, like garden plants, can also be classified by their life cycle: annual, biennial, and perennial. Weed control strategies are often similar for weeds with the same life cycle, so knowing and applying this information can aid you in your weed management activities.<\/p>\n\n\n\n<p><strong><em>Annuals<\/em><\/strong>. Annual weeds progress from seed germination to seed production in less than 12 months; indeed, some annual weeds may germinate and reproduce viable seed in as short as 45 days! The successful reproductive strategy employed by annuals is to produce lots of seed in as short amount of time as possible, then die and get out of the way for the coming generation. There are two major types of annuals: winter and summer.<\/p>\n\n\n\n<p class=\"wsu-spacing-after--large\">Winter annuals are typified by those species whose seed are programmed to germinate during times of cooling soil temperatures, increased soil moisture, and shorter day lengths\u2014common conditions in the fall of the year. Resultant seedlings survive the winter and begin growth again as temperatures warm in late winter through early spring. Seedlings then flower and produce their seeds before soils begin to dry out in mid- to late-spring. After seeding, winter annuals die, sometimes as early as April or May in Washington. These plants take advantage of relatively mild winters (with snowfall keeping them warm in many areas) and time their peak growth and reproduction to occur when most of our natural precipitation occurs\u2014winter and early spring. Some common winter annuals include downy brome (cheatgrass), field pennycress, and common groundsel (<em>Senecio vulgaris<\/em>) (Figure 12) in eastern Washington and common chickweed (Figure 13), annual bluegrass (<em>Poa annua<\/em>) (Figure 14), hairy bittercress (<em>Cardamine hirsuta<\/em>) (Figure 15), shepherd\u2019s-purse, henbit (<em>Lamium amplexicaule<\/em>) (Figure 16), and pineapple-weed (<em>Matricaria discoidea<\/em>) throughout the state.<\/p>\n\n\n\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped wp-block-gallery-3 is-layout-flex\">\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" data-id=\"3427\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_13-3.jpg\" alt=\"Common chickweed with white-petaled flower in center.\" class=\"wp-image-3427\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_13-3.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_13-3-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_13-3-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 13. Common chickweed (<em>Stellaria media<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3428\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_14-3.jpg\" alt=\"Annual bluegrass.\" class=\"wp-image-3428\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_14-3.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_14-3-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 14. Annual bluegrass (<em>Poa annua<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" data-id=\"3432\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_15-2.jpg\" alt=\"Hairy bittercress with small white flower cluster in center.\" class=\"wp-image-3432\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_15-2.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_15-2-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_15-2-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 15. Hairy bittercress (<em>Cardamine hirsuta<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" data-id=\"3430\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_16-2.jpg\" alt=\"Leaves and pink flowers on the end of a stalk.\" class=\"wp-image-3430\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_16-2.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_16-2-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_16-2-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 16. Henbit (<em>Lamium amplexicaule<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3431\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_17-1.jpg\" alt=\"Thick, green stalks of large crabgrass branching at tips into red leaves and seeds.\" class=\"wp-image-3431\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_17-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_17-1-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 17. Large crabgrass (<em>Digitaria sanguinalis<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3429\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_18-1.jpg\" alt=\"Green patch of Powell amaranth.\" class=\"wp-image-3429\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_18-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_18-1-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 18. Powell amaranth (<em>Amaranthus powellii<\/em>).<\/figcaption><\/figure>\n<\/figure>\n\n\n<div class=\"wp-block-image wsu-spacing-before--xxmedium\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_19-1.jpg\" alt=\"Matted prostrate spurge spiderwebbing across the ground.\" class=\"wp-image-3433\" width=\"450\" height=\"280\" \/><figcaption class=\"wp-element-caption\">Figure 19. Prostrate spurge (<em>Euphorbia prostrata<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p class=\"wsu-spacing-before--large\">Summer annuals are those plants whose seeds germinate when soils are moist and day lengths and soil temperatures are increasing, usually in the spring but sometimes not until early summer. Summer annuals take advantage of excellent conditions for growth early in the season and rapidly sink their roots deeply in the soil to maximize plant size and, in turn, total seed production. After setting seed in late summer to fall, most summer annuals die. Common summer annual weeds in Washington include barnyardgrass, large crabgrass (<em>Digitaria sanguinalis<\/em>) (Figure 17), the pigweeds (such as Powell amaranth [Figure 18] or redroot pigweed), common lambsquarters, purslane, hairy nightshade, prostrate spurge (<em>Euphorbia prostrata<\/em>) (Figure 19), and catchweed bedstraw.<\/p>\n\n\n\n<p>Keep in mind that the distinction between winter and summer annual weeds is not hard and fast. Some species that are strictly summer annuals in some climates may be winter annuals in warmer climates. For example, birdsrape mustard (<em>Brassica rapa<\/em>) (Figure 20) is generally a summer annual in the Columbia Basin, but in western Washington, it is just as likely to be a winter annual.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_20-1.jpg\" alt=\"Close-up of cluster of yellow flowers on tip of green stalk.\" class=\"wp-image-3434\" width=\"400\" height=\"400\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_20-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_20-1-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_20-1-150x150.jpg 150w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><figcaption class=\"wp-element-caption\">Figure 20. Birdsrape mustard (<em>Brassica rapa<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p><strong><em>Biennials<\/em><\/strong>. Biennial weeds take 12 to 24 months to progress from seed germination to seed production. Seeds will germinate whenever favorable conditions occur during the first year, often in spring but sometimes after the onset of fall rains. Biennial weeds are strictly vegetative their first season, regardless of when seed germination occurred, usually forming tight rosettes of leaves. Cool and moist soil conditions coupled with short day lengths through the winter predisposes biennial plants to flower during their second year (a process termed vernalization). Vernalized rosettes make good use of the appreciable amount of energy they stored in their crowns and roots in the form of starches and sugars during their first year, and these second-year plants grow quickly. Following bolting, flowering, and seed production, biennials normally die.<\/p>\n\n\n\n<p>Biennials differ from winter annuals in that they require more than 12 months to grow from seeds until they produce seed themselves, while winter annuals require less than 12 months to complete the same process. In addition, vernalization is an absolute requirement for biennials to flower, while some winter annuals can flower without being vernalized. For that kind of winter annual, in fact, reproduction may be delayed by cold winter temperatures. Some common biennial weeds in Washington include wild carrot (<em>Daucus carota<\/em>) (Figure 21, A), poison hemlock (<em>Conium maculatum<\/em>) (Figure 21, B), bull thistle (<em>Cirsium vulgare<\/em>), meadow salsify (<em>Tragopogon pratensis<\/em>), and tansy ragwort (<em>Jacobaea vulgaris<\/em>) (Figure 22).<\/p>\n\n\n<div class=\"wsu-row wsu-spacing-before--large wsu-spacing-after--large wsu-row--halves\" >\r\n    \n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_21A.jpg\" alt=\"White umbels of wild carrot at tip of green stalk.\" class=\"wp-image-3435\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_21A.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_21A-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 21. Umbels of wild carrot (<em>Daucus carota<\/em>, left) and poison hemlock (<em>Conium maculatum<\/em>, right).<\/figcaption><\/figure>\n\n<\/div>\r\n\n\n<div class=\"wsu-column\"  style=\"\">\r\n\t\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_21B.jpg\" alt=\"White umbels of poison hemlock at tip of green stalk.\" class=\"wp-image-3436\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_21B.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_21B-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><\/figure>\n\n<\/div>\r\n\n<\/div>\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_22.jpg\" alt=\"Green tansy ragwort plant.\" class=\"wp-image-3437\" width=\"450\" height=\"300\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_22.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_22-300x200.jpg 300w\" sizes=\"(max-width: 450px) 100vw, 450px\" \/><figcaption class=\"wp-element-caption\">Figure 22. Tansy ragwort (<em>Jacobaea vulgaris<\/em>).<\/figcaption><\/figure><\/div>\n\n\n<p><em><strong>Perennials<\/strong><\/em>. Perennial weeds live longer than two years and remain alive even after they produce seed. Some perennial weeds do not produce seed their first year (as mentioned above, some don\u2019t produce seed at all!), but most will produce seed each year of their life. Perennial weeds are usually subdivided into two categories: woody and herbaceous.<\/p>\n\n\n\n<p>Woody perennials are species with above ground structures that survive winter. Because these shoots are exposed to colder air than are roots, branches of woody perennials are made up of tough (woody) tissue and produce buds to protect tender meristematic tissue from being injured by winter temperatures. In the spring, buds break open and new vegetative and reproductive growth emerges. Examples of woody perennials in Washington include Scotch broom, saltcedar, wild rose (<em>Rosa<\/em> spp.), and Himalaya blackberry (<em>Rubus armeniacus<\/em>).<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_23-ABC-1.jpg\" alt=\"Composite image showing field bindweed plants with white and pink funnel-shaped flowers. Panel A displays multiple plants growing low to the ground among green leaves and stems. Panel B shows a close-up of a pink and white flower with a yellow center, and Panel C shows a white flower with a similar shape and yellow center.\" class=\"wp-image-3439\" width=\"450\" height=\"300\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_23-ABC-1.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_23-ABC-1-300x200.jpg 300w\" sizes=\"(max-width: 450px) 100vw, 450px\" \/><figcaption class=\"wp-element-caption\">Figure 23. Field bindweed (<em>Convolvulus arvensis<\/em>) plants (A) bear pink (B) or white (C) flowers.<\/figcaption><\/figure><\/div>\n\n\n<p>Like woody perennials, herbaceous perennials are weed species that grow from sometimes massive root systems. The roots of herbaceous perennials produce flowering\/fruiting shoots each year but, because they cannot survive cold temperatures, they die back to the ground each winter. Some herbaceous perennial weeds in Washington are field bindweed (<em>Convolvulus arvensis<\/em>) (Figure 23), Canada thistle, dandelion, common catsear (<em>Hypochaeris radicata<\/em>), horsetail (<em>Equisetum<\/em> spp.) (Figure 24), quackgrass (<em>Elymus repens<\/em>), and Bohemian knotweed (<em>Reynoutria<\/em> \u00d7 <em>bohemica<\/em>) (Figure 25).<\/p>\n\n\n\n<p>Perennial weeds can also be classified as to whether they are simple or creeping. Simple perennials spread primarily by seed, although they can produce multiple crowns on the same root. Simple perennials include dandelion, broadleaf plantain (<em>Plantago major<\/em>) (Figure 26), curly and broadleaf dock (<em>Rumex crispus<\/em> and <em>R. obtusifolius<\/em>), spotted knapweed, St. Johnswort, and bittersweet nightshade. Creeping perennials, on the other hand, spread vegetatively as well as by seed. Common creeping perennials are Canada thistle, horsetail, field bindweed, quackgrass, white clover (Figure 27), and creeping buttercup (<em>Ranunculus repens<\/em>) (Figure 28).<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full\"><img decoding=\"async\" loading=\"lazy\" width=\"400\" height=\"502\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_24AB-1.jpg\" alt=\"Composite image showing two growth stages of horsetail. Panel A depicts fertile, tan-brown stems with cone-shaped, spore-producing tips emerging among green foliage. Panel B shows mature, green, feathery vegetative stems growing densely along a fence line.\" class=\"wp-image-3447\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_24AB-1.jpg 400w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_24AB-1-239x300.jpg 239w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><figcaption class=\"wp-element-caption\">Figure 24. Giant horsetail (<em>Equisetum telmateia<\/em>) fronds, fertile (A) and infertile (B).<\/figcaption><\/figure><\/div>\n\n\n<h2 class=\"wp-block-heading  wsu-heading--style-marked\" id=\"ch19-weed-management\">Weed Management<\/h2>\n\n\n\n<p>Since we will always have weeds to contend with, the wise gardener develops a strategy by which such plants can be managed and their adverse effects minimized. Whenever possible, the following strategies should be considered before beginning a landscaping or other garden project, but it is a rare site indeed where weed control efforts won\u2019t be beneficial even if applied after such a project is already in place. The following pages will categorize and describe several different management strategies which will aid in your struggle with weeds.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Prevention<\/em><\/h3>\n\n\n\n<p>The old saw about \u201can ounce of prevention being worth a pound of cure\u201d is abundantly true with regard to weed management. And any good weed control program must begin with a positive identification of the plant(s) in question. Never be content letting a weed go unrecognized\u2014if you don\u2019t know what it is, find out. Remember that a weed population is far, far easier to kill before it has had a chance to establish itself on a site. Even the worst weed infestations in Washington, from yellow starthistle on the rangelands to Scotch broom along the forest highways to field pennycress on the farms, probably began with the introduction of just a few individual plants. If control measures had been implemented at the time the species was first detected, it might have been eradicated and the infestation avoided altogether. Given our state\u2019s location at the edge of the continent, we no doubt receive introductions of many potential weed species on an annual basis. It pays to be vigilant! Who knows? You may prevent the invasion of the next weed species with potential to be as bad as spotted knapweed.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"alignright size-full is-resized\"><img decoding=\"async\" loading=\"lazy\" src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_25-4.jpg\" alt=\"Broad, oval leaves and dense, showy, white flowered clusters of bohemian knotweed.\" class=\"wp-image-3455\" width=\"450\" height=\"300\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_25-4.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_25-4-300x200.jpg 300w\" sizes=\"(max-width: 450px) 100vw, 450px\" \/><figcaption class=\"wp-element-caption\">Figure 25. Bohemian knotweed (Reynoutria \u00d7 bohemica).<\/figcaption><\/figure><\/div>\n\n\n<p class=\"wsu-spacing-after--large\">We are often our own worst enemies in regard to spread of weeds. While there is ample evidence that weedy plants get around very well on their own devices, people are very good at aiding them in their spread. A weed\u2019s travel is enhanced through movement of equipment and vehicles (think about that soil aerator you just rented or those weeds you ran over during your drive in the woods the other day); through contaminated seedlots, plant materials, mulch, or animal feed\/bedding (think about that cut-rate lawn seed you bought or that bargain beauty bark you spread on your rhodies that turned out to be bristling with new horsetail shoots a month later); or simply because we don\u2019t know the whole story (think about that \u201ccute\u201d little ground cover in your friend\u2019s garden that you transplanted into your yard not realizing that it was trouble until it had overgrown your entire perennial landscape).<\/p>\n\n\n\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped wp-block-gallery-5 is-layout-flex\">\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3456\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_26-4.jpg\" alt=\"Broad, prostrate leaves of broadleaf plantain with vertical seed stalks protruding from center of plant.\" class=\"wp-image-3456\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_26-4.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_26-4-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 26. Broadleaf plantain (<em>Plantago major<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"600\" data-id=\"3457\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_27-3.jpg\" alt=\"Close-up of two clover flowers with white and pink rounded blooms and green trifoliate leaves, set against a clear blue sky. One flower is fully open, while the other is partially closed.\" class=\"wp-image-3457\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_27-3.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_27-3-300x300.jpg 300w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_27-3-150x150.jpg 150w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 27. White clover (<em>Trifolium repens<\/em>).<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"600\" height=\"400\" data-id=\"3458\"  src=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_28-3.jpg\" alt=\"Close-up of creeping buttercup (Ranunculus repens) plants with clusters of small, bright yellow flowers and glossy, deeply lobed green leaves covering the ground.\" class=\"wp-image-3458\" srcset=\"https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_28-3.jpg 600w, https:\/\/wpcdn.web.wsu.edu\/extension\/uploads\/sites\/62\/2025\/10\/Figure_28-3-300x200.jpg 300w\" sizes=\"(max-width: 600px) 100vw, 600px\" \/><figcaption class=\"wp-element-caption\">Figure 28. Creeping buttercup (<em>Ranunculus repens<\/em>).<\/figcaption><\/figure>\n<\/figure>\n\n\n\n<p class=\"wsu-spacing-before--large\">Preventing the spread of weeds is the concept behind noxious weed laws. <em>Noxious weeds<\/em> are non-native species declared by the state to be plants that cause harm to the state\u2019s agricultural, range or forest lands, roadsides, or waters. The responsibility of controlling noxious weeds rests with the owner of the land on which the noxious weed is found. In Washington, the law has three tiers, or classes, of weeds: A, B, and C. Class A designations are for weeds with very small distributions. The goal is to eradicate these species before they become too widespread. Class B weed species may be locally abundant but are not found throughout the state. Some counties, then, may choose not to require control of the species since nearly everyone already has it (Class B non-designate), but other counties may designate that species for control because they have no, or very small, local infestations (Class B designate). Another Class B designate might be a weed that may cause severe local harm if left to grow unchecked. Wild carrot, for example, is a Class B weed in Washington primarily because, if growing close to carrots being grown as a vegetable seed crop, it may cross-pollinate with the carrot crop, rendering the resultant seed useless. To avoid such losses, it is listed a Class B designate in counties producing carrots or carrot seed but Class B non-designate elsewhere. Finally, Class C weeds are those that may or may not be widespread in the state but are a priority for certain counties to control. The <a href=\"https:\/\/www.nwcb.wa.gov\/\" data-type=\"URL\" data-id=\"http:\/\/www.nwcb.wa.gov\/\" target=\"_blank\" rel=\"noreferrer noopener\">Washington State Noxious Weed Control Board (opens in new window)<\/a> website has a <a href=\"https:\/\/www.nwcb.wa.gov\/printable.htm\" data-type=\"URL\" data-id=\"http:\/\/www.nwcb.wa.gov\/printable.htm\" target=\"_blank\" rel=\"noreferrer noopener\">printable list of noxious weeds (opens in new window)<\/a>.<\/p>\n\n\n\n<p>One other designation of importance to gardeners is the plant quarantine list. Quarantined species are particular weeds that are usually ornamental; that is, they may bear bright foliage or produce attractive flowers that would entice many people to plant them in their landscape. Once planted, they almost invariably escape to become new weed infestations. In Washington, it is illegal to move, buy, sell, or offer to sell a species on the quarantine list. Visit the <a href=\"http:\/\/www.nwcb.wa.gov\/searchResultsQuarantine.asp\" data-type=\"URL\" data-id=\"http:\/\/www.nwcb.wa.gov\/searchResultsQuarantine.asp\" target=\"_blank\" rel=\"noreferrer noopener\">Quarantine List (opens in new window)<\/a> for Washington State for more information.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Mechanical Control<\/em><\/h3>\n\n\n\n<p>Mechanical weed control is physically doing something to an individual weed in order to kill it (this method is also, logically, referred to as \u201cphysical weed control\u201d). Cultivation is the most common method of mechanical weed control, typically hand-pulling, hoeing, or rototilling. These methods uproot the weeds, causing them to dry out and, hopefully, die. Cultivation, therefore, is more effective on dry days than on rainy days; plants left on moist soil surfaces are more likely to re-root than plants left on a dry soil surface. In the same way, warm, sunny days are better for hand-weeding than cool, overcast days. For optimal results, weed early in the day so uprooted weeds are exposed to maximal water stress during the heat of the day rather than weeding in the evening, which provides freshly uprooted plants time to recover during nighttime hours when cooler, darker, and more humid conditions prevail. The smaller the individual weed, the more susceptible it is to mechanical weed control. It is the seedling in the cotyledon stage of growth that is most vulnerable to cultivation, because older plants have substantial stored energy and water in leaves, stems, and roots which allow that plant to re-root or regrow from a root or crown fragment. Keep in mind, too, that while soil disturbance may kill the emerged weed, it also brings new weed seeds to the soil surface where they can then germinate and leave the site as weedy as it was before. So be careful not to hoe too deeply!<\/p>\n\n\n\n<p>Controlling established perennial species using mechanical weed control methods is tough, especially controlling those perennials with vegetative reproductive structures. Such perennials generally have considerable stored energy in their roots, so they are able to recover from considerable injury, even total defoliation. Perennial roots must expend substantial energy to accomplish that regrowth, however, and unless they are able to replace that energy through photosynthesis within their regrown shoots, carbohydrate reserves in those roots can be depleted to the point of root death. Since shoots continue to use the stored energy from roots until the first leaves have fully expanded, mechanical control efforts should be timed to coincide with that stage of growth. This maximizes the stress on those perennial roots. Certain perennials, such as Canada thistle and field horsetail (<em>Equisetum arvense<\/em>), are actually quite sensitive to defoliation, provided that all shoots are removed whenever they become photosynthetically self-sufficient. This requires persistence on the part of the gardener\u2014occasionally hand pulling a few shoots over the course of a summer won\u2019t do the trick.<\/p>\n\n\n\n<p>Rototilling cuts weed roots and foliage into small pieces and buries them. This usually results in excellent control of most small annual and biennial weeds. Unfortunately, perennial weeds with vegetative reproductive structures greatly benefit from rototilling, since cutting their rhizomes or roots into small pieces creates a massive number of new shoots for you to contend with a week or two later. Bulbs and tubers can also be scattered from the mother plant to new sites through the tillage operation. Unless employed frequently, rototilling established perennial weeds is not advisable.<\/p>\n\n\n\n<p>Mowing is another method of mechanical weed control. It is most often used in turf, but can also be used along roadsides, bare areas, or under trees. While most weeds regrow after mowing, seed production can be drastically reduced by timely removal of top growth. Annuals in particular tend to be susceptible to mowing through the summer, since they can\u2019t produce seed if flower stalks are continually mowed. Exceptions are those weeds with a prostrate growth habit (such as prostrate knotweed [<em>Polygonum aviculare<\/em>] or puncturevine [<em>Tribulus terrestris<\/em>]), since most of their foliage is found below the blade of a lawn mower. It is especially doubtful that low-growing perennials (such as white clover, creeping buttercup, dandelion, or many of the speedwell [<em>Veronica<\/em>] species) sustain much damage from mowing.<\/p>\n\n\n\n<p>Another mechanical method of weed control is the use of mulch. Mulches function by depriving light from the weed seedling or non-germinated seed, and usually consist of gravel, pumice, bark, or wood chips. Organic mulches have the added benefit of slowing water loss from soil, which helps keep the soil cool and moist during hot summer months. These products are best spread thinly, prior to weed seed germination, usually around the bases of woody landscape plants. If applied too thickly, mulches reduce gas exchange with the soil which can injure shallowly rooted ornamentals. In cool maritime climates particularly, mulches also may result in soils that are excessively cool and wet, increasing the incidence and severity of root or crown diseases in desirable vegetation. Be sure your organic mulches are weed free! You want to avoid introducing weed seeds or other propagules into your garden by using contaminated mulch.<\/p>\n\n\n\n<p>Mulches also improve weed control in vegetable gardens and, if used with drip irrigation, increase water use efficiency. Typically, black weed fabric is used instead of clear plastic to prevent light from reaching weeds that may otherwise grow beneath the plastic. To use fabric mulch in this situation, first work the soil into a good seed bed and then lay out drip tape where you will be placing the vegetable plants. Then spread the fabric over the top of the bed and anchor it along the sides and on the ends. Cut slits or holes through the fabric and plant the vegetable seedlings.<\/p>\n\n\n\n<p>If placed before weed seeds germinate, control of annual weeds with weed fabric in the landscape or vegetable garden is excellent. Control of established perennial weeds varies, depending on the thickness of the fabric and the ability of weeds to \u201cpunch\u201d through the fabric. Plants with sharp-tipped rhizomes, such as quackgrass or yellow nutsedge (<em>Cyperus esculentus<\/em>) for example, will be more successful at growing through weed fabric than creeping perennials not so well-equipped, such as Canada thistle, field horsetail, and field bindweed. Loose mulch, either organic or rock, will not provide much control of established perennials.<\/p>\n\n\n\n<p>In warmer regions of Washington, clear plastic may be used for soil solarization, in which transmitted sunlight heats the soil via the greenhouse effect. Soil sterilization may be helpful to reduce populations of soil pathogens, insects, and even the vegetative reproductive structures and seeds of certain weed species. In cooler regions of the state, however, clear plastic simply provides weeds with a nice warm place in which to grow and so is not recommended.<\/p>\n\n\n\n<p>Flaming young weeds is also effective in certain situations. Flame is most often generated by burning propane, usually using a wand that is attached to the tank via a long hose. Flame is directed toward emerged weeds, resulting in \u201cmelting\u201d of the wax cuticle on the leaf surface and simultaneous bursting of leaf cells by disrupting cellular membranes, resulting in desiccation of the leaf. When used against weed seedlings from the cotyledon stage of growth to about three leaves, control can be excellent, although control of grass seedlings is usually poor since the growing point of grasses is often below the soil surface. When using flame, keep a few things in mind, however. First, flame does not kill non-germinated weed seeds or roots of emerged weeds. Soil is an effective insulator from the heat of the flame, so flame works best against young weeds that do not have large roots from which they will regrow. A single flaming is seldom effective against established biennial or perennial weeds, or even against large annual weeds. Second, there is no need to literally burn up the emerged weed seedlings. A brief one- or two-second flaming will melt the cuticle of the cotyledon or leaf (look for the brightness of the melted wax, much like from burning candle, to know when your flame has achieved its effect) and the flamed plant will completely wilt within minutes. Third, it is definitely not advisable to use flame for weeding on or near flammable objects or combustible materials, such as wood structures, wood chip or plastic mulches, or dry leaves or needles, as accidental fires may result. Be sure to check with local authorities to determine if flaming is allowed in your area.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Cultural Control<\/em><\/h3>\n\n\n\n<p>Cultural methods of weed control manage the level of competition between desired plants and weeds. The idea is to make conditions as favorable as possible for shrubs, turf, or vegetables while making things as difficult as possible for the weeds. The result will be that desirable plants are made more competitive and their growth and development will therefore be favored over the weeds. Gardeners can achieve this in several ways. First, be sure your desirable vegetation is as healthy as it can be\u2014whether we\u2019re talking about landscape plants, turf, or vegetables. Choose plants that are well-adapted to their environment, fertilize and irrigate them properly, mow lawns to keep the growth vigorous, and prevent outbreaks of diseases or insects which decrease overall plant health and competitive ability.<\/p>\n\n\n\n<p>A second means of employing cultural weed control is to use transplants when possible. Remember that weeds compete with desirable plants for physical space, and space capture usually goes to the first plant that shows up to occupy it. Often that first plant is a weed, and often that weed emerges several days sooner than does our carefully planted crop seed. Weed seedlings often also grow faster than crop seedlings, which results in dominance of the soil by weeds. When gardeners use transplants, space capture usually goes to the crop plant, and since transplants usually grow faster than younger weed seedlings, the competitive ability of the crop is improved at the expense of the weed.<\/p>\n\n\n\n<p>Another trick gardeners can use to improve weed control culturally is to practice crop rotations. Weeds often will do best when growing with crop plants that share similar life cycles and growing conditions. For example, when hardy vegetables such as lettuce, spinach, or peas are seeded in late winter or early spring, early germinating weed species (usually winter annuals such as common chickweed, shepherd\u2019s-purse, and field pennycress) tend to dominate the weed spectrum because these species prefer cool soils. In fact, seeds of later germinating weed species (such as barnyardgrass or purslane) may not even get an opportunity to germinate, since the crop plants and winter annuals have already captured the space and are providing shade to the soil surface, making conditions unfavorable for further seed germination. Conversely, when non-hardy vegetables such as squash, sweet corn, or beans are seeded in late spring to early summer, late germinating weed species (such as redroot pigweed or green foxtail) tend to dominate because the weeds that germinated prior to crop seeding are killed by the cultivation of seedbed preparation, leaving the site open for colonization when the soil is warm. Weeds also tend to \u201chide\u201d in the foliage of similar-appearing plants. Hairy nightshade (<em>Solanum physalifolium<\/em>) is notorious for growing amongst closely related and visually similar tomatoes and potatoes, making the nightshade hard to see and remove until after it has already flowered and matured its seed. For these reasons, it\u2019s a good idea to rotate your vegetables with an eye toward their life cycle to avoid continuously selecting for particular weed species.<\/p>\n\n\n\n<p>Winter cover crops can also be used to aid in weed control. Planting winter-hardy, densely growing crops in the fall allows them to capture space in your garden and reduce the amount of weed growth compared with bare soil. This is particularly true in central and eastern Washington, where winters are cold enough to slow the growth of, or even kill, weeds that germinated at the same time as the cover crop. In western Washington, weed control resulting from cover cropping will usually not be as great as in other parts of the state, although nutrient capture and improved organic matter production remain as two important benefits to cover cropping. Even in western Washington, however, mustard cover crops significantly reduce weed growth in winter and spring, due primarily to production of large leaves and thorough ground coverage by that crop. Disadvantages of cover cropping include delayed crop seeding in the spring (cover crops must be incorporated into the soil and it takes time for foliage to break down), hindered crop seed germination from allelopathic or biofumigant qualities of the cover crop, and increased populations of pest insects or slugs which may benefit from the cover provided.<\/p>\n\n\n\n<p>Ground covers can often be used to good effect\u2014both aesthetically and as a tool against weeds. Good ground covers do exactly that: they cover the ground and don\u2019t allow light to reach the soil surface, thereby limiting the germination of most weedy species. Ground covers also compete well with weed seedlings, making them less likely to establish and reproduce themselves. The biggest concern about ground covers may be that they could become weedy in their own right. Be sure to thoroughly investigate unproven ground covers to see if they are weedy elsewhere in the United States or in similar climates throughout the world before using or recommending them for planting.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Biological Control<\/em><\/h3>\n\n\n\n<p>Biological weed control, or biocontrol, uses an organism to act on or control a weed species. The classic use of biological control organisms is against non-native weeds of range and forest lands\u2014usually after that weed has infested thousands of acres and other methods of weed control won\u2019t be cost-effective. Recall that most weed species are not native to where they are weedy, due, in part, to lack of damaging insects or diseases in their new habitat that might slow their spread. Entomologists and plant pathologists travel to a weed\u2019s country of origin to identify insects and disease pathogens that are detrimental to the health of that weed species and prevent it from dominating its native land. These organisms are then tested in greenhouses to determine whether they will exclusively feed on or infect our out-of-control weed and not damage closely related crops or native plant species. Suitable organisms are then released with the hope they will at least slow the spread of some particularly nasty noxious weed species. Biocontrol organisms can be particularly helpful in the management of noxious weeds where other types of weed control may not be feasible, such as in sensitive wetlands or sites inaccessible to sprayers or cultivation equipment.<\/p>\n\n\n\n<p>Grazing animals can also be used for weed control. Goats preferentially graze broadleaf plants and often are less affected by plant toxins that may injure horses or cattle, so they have been used to selectively remove range weeds such as leafy spurge (<em>Euphorbia esula<\/em>) or tansy ragwort (<em>Jacobaea vulgaris<\/em>). \u201cWeeder geese\u201d have also been used to forage for grassy weeds in perennial plantings or broadleaf row crops. In cases such as these, careful management is necessary to ensure that the animals don\u2019t cause damage to the desirable vegetation.<\/p>\n\n\n\n<p>In general, biological weed control has less to offer backyard gardeners than other methods of weed control. First, biocontrol does not normally result in complete weed control. Because they are living entities, biocontrol organisms require a low population of the weed be maintained to provide food for their progeny; such a population of these weed species would not be acceptable in most urban or suburban sites. Second, most backyard weed species don\u2019t have biocontrol agents available for their control, and most gardeners don\u2019t have the weeds for which biocontrol agents have been developed. Finally, having goats, geese, or the like grazing in their backyard is not something that a typical homeowner can legally do even if they wanted to, and the likelihood that such grazing animals would cause damage to horticultural species is high. Still, gardeners with larger tracts of land may find biological control helpful.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Chemical Control<\/em><\/h3>\n\n\n\n<p>Chemical weed control involves the use of herbicides to disrupt certain plant functions, thereby killing the treated plant. While many herbicides are registered for commercial use in various agricultural, horticultural, and non-crop situations, homeowners have access to only a fraction of these products. As with any chemical, gardeners using herbicides should use care in the mixing and application process to prevent accidental exposure to themselves or others, and to avoid injury to desirable vegetation. The label on an herbicide is a legal document. Gardeners\/users must read, understand, and follow the label instructions on the product. The label is the law.<\/p>\n\n\n\n<h4 class=\"wp-block-heading wsu-font-size--xxmedium wsu-spacing-after--small\">Herbicide Types<\/h4>\n\n\n\n<p>Herbicides are usually one of two types: contact products or translocating products. <a href=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#c\" data-type=\"URL\" data-id=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#c\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Contact herbicides<\/strong> (opens in new window)<\/a> are applied directly to weed foliage and result in leaf\/shoot death or damage. Once absorbed, contact herbicides do not move around inside the plant, for example, from the leaves to the roots. Consequently, control of established perennial weeds usually will require multiple applications of a contact herbicide, since roots will not be affected and will produce new shoots that must be treated again. If all shoots are consistently removed as they appear, the perennial root will eventually run out of energy and die, similar to what would result from constantly cutting off shoots with a hoe. Similarly, control of larger annuals or biennials can be difficult when using contact herbicides; these weeds are best controlled by contact herbicides at early growth stages. These products should be applied to adequately cover as much of the shoot as possible, but not so much that it runs off the plant leaf (contact herbicides generally have very limited soil activity, if any). Examples of home and garden contact herbicides include diquat, glufosinate, oxyfluorfen, potassium salts of fatty acids, vinegar (acetic acid), eugenol, limonene, and citric acid.<\/p>\n\n\n\n<p><a href=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#t\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Translocating herbicides<\/strong> (opens in new window)<\/a> are absorbed into the plant and then move from roots to leaves, from leaves to roots, or from leaves to other sites of meristematic activity. Such products, then, are either designed to be applied to soil (usually before weeds emerge from the ground, <em>preemergence<\/em>), or to the foliage of emerged weeds (<em>postemergence<\/em>). Some common home and garden soil-applied products include dichlobenil, trifluralin, and oryzalin; foliar-applied products include 2,4-D, MCPA or MCPP, dicamba, triclopyr, and glyphosate.<\/p>\n\n\n\n<p>Another category to consider for herbicides is whether the product is selective or non-selective. <em>Selective herbicides<\/em> provide control of certain weeds but don\u2019t damage other vegetation. An example of a selective herbicide is 2,4-D, which selectively kills broadleaf weeds in turf while not injuring the grass. Most herbicides labeled for use by homeowners are selective products. Alternatively, <em>non-selective herbicides<\/em> damage plants of all kinds. Some are contact products such as diquat; others are translocating like glyphosate (Roundup). These products must be applied with great care to avoid unintentionally spraying foliage of desirable vegetation.<\/p>\n\n\n\n<p><a href=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#f\" data-type=\"URL\" data-id=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#f\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Foliar-applied herbicides<\/strong> (opens in new window)<\/a>, typically, are liquid formulations. They are available either as premixed (ready-to-use or RTU) sprays or concentrates that must be mixed with water before application. Read and follow the product label directions to determine how much concentrate you should add to a given amount of water, and how and when to apply the specific mixture.<\/p>\n\n\n\n<p><a href=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#s\" data-type=\"URL\" data-id=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#s\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Soil-applied products<\/strong> (opens in new window)<\/a> are available to homeowners typically as granular products. Most are very volatile, and placement on clay or finely ground materials helps to stabilize the active ingredient and keeps it from evaporating immediately after application, as can happen with liquid sprays. Granules are made to be applied dry to the soil, then incorporated using tillage equipment, or by irrigation or rainfall.<\/p>\n\n\n\n<p><a href=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#w\" data-type=\"URL\" data-id=\"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/glossary\/#w\" target=\"_blank\" rel=\"noreferrer noopener\"><strong>Weed-and-feed products<\/strong> (opens in new window)<\/a> are fertilizers that have been mixed with broadleaf herbicides such as 2,4-D or dicamba. Weed-and-feeds are formulated to be applied just like any commercial fertilizer blend\u2014preferably using a drop-type spreader rather than a cyclone-type spreader which may fling the product into places you don\u2019t want it to go. Some weed-and-feed products are formulated to be applied using a hose-end sprayer. Check the label for the product you are using and apply as directed. In any case, be very careful not to over-apply weed-and-feeds! Calibrate your spreader based on the herbicide content of the mix, not its nitrogen content. (Refer to Chapter 4: Plant Mineral Nutrition and Fertilizers for instructions on how to calibrate a spreader). Also, be cautious applying these products near desirable broadleaf vegetation, as desirable plants may be injured by root or foliar uptake of the herbicide in the mix. Keep in mind that roots of plants in the landscape, or in the lawn itself, intermingle with grass roots and often extend beyond the \u201cdrip line.\u201d Indeed, roots of some woody ornamentals may extend even farther than the height of the tree or bush.<\/p>\n\n\n\n<p>Several \u201cnatural herbicides\u201d may have caught your attention over the years. The first to come out was acetic acid, which can also be called vinegar in some situations. Let\u2019s take a minute to talk about when it\u2019s called vinegar and when it\u2019s called acetic acid to avoid any later confusion. The chemical name is acetic acid, but EPA and FDA call it vinegar when the concentration is below 8%. This is what you buy in the grocery store for cooking purposes. When the concentration is above 8% it\u2019s called acetic acid and this higher concentration is what is used as an herbicide. The distinction is important for several reasons. Grocery store vinegars are not registered pesticides so you can\u2019t recommend their use as such. Acetic acid products are sold in several strengths. Research shows that 5% acetic acid concentrations are not strong enough to be very effective as a foliar herbicide but when used as a soil drench will perform a little better. Control is best when the acetic acid product is applied to weed seedlings up to about 2 or 3 leaves in size. For treatment areas having a larger number of weeds, the cost of drenches may be excessive when compared to other registered herbicides. Other \u201cnatural herbicides\u201d available in Washington include eugenol (cinnamon and clove oils), citric acid, and limonene, among other materials. All have shown activity on small weeds up to about to the 3-leaf stage of growth, but repeat applications will be necessary to provide control of larger annual, biennial, or perennial weeds.<\/p>\n\n\n\n<p>Corn gluten meal (CGM) is another organic herbicide, but it is NOT currently a registered product in Washington State and is NOT recommended. However, it is worth being aware of because many gardeners have heard of CGM. CGM is the protein fraction of grain corn that remains after the carbohydrates are extracted. It is usually ground fine (similar to corn meal) and applied as a granular product, chiefly to turf and in vegetable gardens. In the laboratory, CGM reduces elongation of the roots from germinating seeds of many species, resulting in weed seedlings that are less able to withstand periods of drought. CGM therefore has no ability to control established weeds, only germinating seeds. Unfortunately, CGM has not been shown to be particularly effective at killing weed seedlings outside the lab, even when applied at high rates. In studies conducted in western Washington, CGM has not provided enough weed control, even of annual species, to be properly considered an herbicide. In turf, it is suspected that any weed control associated with use of this product is probably related more to improved fertility and resulting turf competitiveness (CGM is 10 to 12% nitrogen) than to any direct herbicidal effect by the product. Release of nitrogen by CGM causes grass plants to grow more luxuriantly and to compete better with annual weeds.<\/p>\n\n\n\n<h4 class=\"wp-block-heading wsu-font-size--xxmedium wsu-spacing-after--small\">Mixing and Applying Herbicides<\/h4>\n\n\n\n<p class=\"wsu-spacing-after--xsmall\">Always read and follow label directions for any chemicals. When mixing liquid herbicide concentrates for use in a backpack or other pressurized sprayer, follow these steps:<\/p>\n\n\n\n<ul>\n<li>Add approximately half the water to the spray tank.<\/li>\n\n\n\n<li>Add the measured amount of concentrate to the spray tank.<\/li>\n\n\n\n<li>Add the rest of the water to the spray tank.<\/li>\n\n\n\n<li>Put the lid on the spray tank, and shake vigorously to fully mix the product.<\/li>\n\n\n\n<li>Pressurize the tank.<\/li>\n\n\n\n<li>Apply the herbicide.<\/li>\n<\/ul>\n\n\n\n<p>Liquid, foliar-applied products usually require about six hours of contact time to fully move into plant tissues. Avoid spraying during wet weather or after recent irrigation\u2014spraying wet foliage results in runoff of the herbicide, while rainfall or irrigation shortly after application washes the herbicide from the plant. Most herbicides can be bound up by soil and organic matter, so weeds that are dusty or crusted with dried mud will not be fully controlled. Consequently, foliar-applied liquid sprays work best when applied to clean, dry weeds that are actively growing.<\/p>\n\n\n\n<p>The potential for drift of herbicide sprays should always be kept in mind. There are two kinds of drift: physical drift and vapor drift. Physical drift occurs when the mist from a liquid herbicide application doesn\u2019t land where you wanted to apply the product. This is most likely to occur if you are spraying when winds are over about seven miles per hour, or in very calm (inversion) conditions when small droplets may linger in the air for several minutes or even hours. Inversions frequently occur during early morning hours, and often about sunset. Under inversion conditions, occasional breaths of wind may move these suspended droplets quite a distance from where you sprayed the product. If these droplets move to a susceptible species, that plant can be injured. Vapor drift occurs when environmental conditions cause the applied herbicide to volatilize or evaporate from either the vegetation or soil surface. Vapor drift is maximized when a volatile herbicide is sprayed during humid conditions, followed by bright sun and warm temperatures. Spraying when soil is saturated with water also tends to cause more vapor drift than spraying when the soil surface is dry.<\/p>\n\n\n\n<p>There are several things you can do to minimize drift. First, don\u2019t apply herbicides when winds are greater than seven miles per hour, or when the air is very still. A light breeze is usually better than no wind at all, since the spray droplets more quickly disperse and evaporate in a breeze than during dead calm conditions. Second, do not use too fine a mist because the smallest droplets are more prone to float off target. Instead, use a coarser spray at lower pressure to reduce the formation of these small droplets. Finally, to avoid vapor drift, don\u2019t spray wet soils or when the day is supposed to get hot.<\/p>\n\n\n\n<p>It is important to obtain an even distribution when applying granule products to prevent over-application in some spots (potentially causing injury to nearby desirable plants) and under-application in others (resulting in lack of weed control). Be especially careful during windy conditions, as granules are usually quite light and may blow to where you don\u2019t want them! Do NOT mix granular products with water and attempt to spray them.<\/p>\n\n\n\n<p>Preemergent herbicides need to be applied before seed germination occurs, because most kill weeds by inhibiting the germination process and by preventing normal seedling growth. When optimally applied, an herbicide will kill susceptible weeds before they even have a chance to emerge from the soil. If the site has weeds that have already emerged, these will first have to be removed via shallow tillage, hand weeding, or a postemergence herbicide.<\/p>\n\n\n\n<p>To maximize a preemergent herbicide\u2019s effectiveness, get the herbicide near the germinating seed. Since most weed seeds germinate in the top inch or two of soil, this is where the herbicide should be placed. If the herbicide is placed too shallowly, seeds germinating below the herbicide zone will have normal roots and the plants may not absorb enough herbicide through their shoots to kill them. Conversely, if the herbicide is placed too deeply, the herbicide may become diluted to the point where a plant does not absorb a lethal dose.<\/p>\n\n\n\n<p>In addition to getting the herbicide next to the weeds, most granular products require incorporation into the soil to prevent the loss of volatile components. Incorporation is usually easiest using irrigation or rainfall. Most granular products work best if incorporated to a depth of two to three inches, which requires about one inch of rainfall or irrigation. If rainfall is spotty, successful incorporation can occur over several days\u2014as long as conditions remain cool and moist. If only light rain is received and temperatures begin to warm, it\u2019s a good idea to finish the incorporation using a sprinkler. Again, follow the label\u2019s instructions for successful incorporation. If applying the granules to the bare ground around newly planted ornamentals, a rototiller or garden rake may be used. If rainfall is not expected within a few days after incorporation and soils are not particularly moist, it may be necessary to irrigate to fully activate the herbicide before many weed seedlings begin to emerge from the soil.<\/p>\n\n\n\n<p>Except for dichlobenil and certain weed-and-feed products which do a good job of controlling many herbaceous perennial weeds, most granular products will only suppress established perennials, not kill them. If you have lots of perennial weeds, you might wish to consider other products.<\/p>\n\n\n\n<p>To be successful, herbicide applications should coincide with the time when the weed is the weakest or most susceptible to the herbicide\u2019s action. All seedlings are easiest to control shortly after germination because very young plants have scant energy reserves available for growth and development. It is not until a plant gets older and begins to produce leaves that it becomes able to make all its own food via photosynthesis. As the seedling continues to grow, it is increasingly able to survive any type of control methods used against it. Consequently, control of seedling weeds using herbicides is best accomplished with soil-applied products used before weeds emerge from the soil, or with foliar-applied products used soon after emergence.<\/p>\n\n\n\n<p>Control of second-year biennials and established perennial weeds generally requires treatment with a foliar-active herbicide that translocates from shoots to roots. After application to leaves, this type of herbicide moves within the plant to kill growing points both above and underground, reducing the weed\u2019s ability to resprout. However, a single herbicide treatment will not generally result in complete perennial weed control. Repeat applications are nearly always necessary to rid a site of established perennial weeds.<\/p>\n\n\n\n<p>Regardless of what type of herbicide you choose, be very careful to apply the proper amount of herbicide to the site! Poor weed control will result from an under-application, and injury to desirable vegetation may result from an over-application. Too, if certain types of herbicides are over-applied, the herbicide can \u201ccarryover\u201d in the soil much longer than normal, with the potential for injuring seeds or transplants long after the application. Applying too much product can also increase the risk of off-site movement of the herbicide, either through storm or irrigation runoff or in water percolating down and into groundwater. Finally, because over-application of herbicide does not control weeds any better than the labeled rate (after all, dead is dead), it ends up wasting your money.<\/p>\n\n\n\n<p>Also, when using foliar applied herbicides, be sure to avoid walking through newly sprayed sites as herbicides can wet your shoes and then move to nontreated sites as you walk. No one wants to see \u201cfootprints\u201d in turf resulting from your walking through glyphosate-treated vegetation and then across your lawn!<\/p>\n\n\n\n<h4 class=\"wp-block-heading wsu-font-size--xxmedium wsu-spacing-after--small\">Personal Safety<\/h4>\n\n\n\n<p>You can minimize exposure of people to herbicides in several ways. Wear protective clothing (shoes, socks, long sleeves, and long pants) and eye protection when mixing and applying herbicides. Granular products are normally watered-in, so direct exposure to these herbicides after application and incorporation is minimal. Exposure to liquid herbicide sprays can be minimized by following label directions and keeping pets and people away from treated areas until sprays have dried. Remember that herbicides, as well as any other pesticides, must be stored out of the reach of children and pets and must be kept in their original containers. Check the label for specific recommendations.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><em>Integrated Weed Management<\/em><\/h3>\n\n\n\n<p class=\"wsu-spacing-after--xsmall\">Integrated weed management involves combining two or more methods of weed control to more effectively manage weeds in lawns, landscapes, or gardens. These combined strategies should be employed in such a way as to target the weed when it is most susceptible to being controlled by each particular strategy. A three-part integrated weed management plan for a larger vegetable garden infested with winter annual weeds might be formulated as follows:<\/p>\n\n\n\n<ol>\n<li>Till the garden in the spring (mechanical weed control).<\/li>\n\n\n\n<li>Wait three weeks for weed seeds brought to the surface to germinate, then spray the area with an approved herbicide (chemical weed control).<\/li>\n\n\n\n<li>Transplant vegetable seedlings after waiting the number of days specified on the label (cultural weed control).<\/li>\n<\/ol>\n\n\n\n<p>This plan is one of a myriad of \u201cstale seedbed\u201d programs that could be designed. Note that in the plan above you could kill the emerged weeds using shallow tillage or flame instead of herbicide if you prefer, or follow the initial weed germination period with repeated tillage and a second waiting period to more thoroughly exhaust the supply of weed seeds. The point is to tailor the weed control program to the site by implementing strategies that control the weed species present without causing damage to other vegetation. Keep in mind that overall management objectives, soil type, temperatures, and precipitation patterns may all influence the selection and suitability of a particular strategy.<\/p>\n\n\n\n<p>It is very important to keep weed management goals realistic! Most people overestimate the effectiveness of any weed control program, while at the same time underestimating the amount of labor generally required to make that program effective. Nowhere is this more true than with herbicides. It will help to realize that herbicides are simply a tool that can help to control weeds, and to avoid thinking that they are a \u201csilver bullet.\u201d Complete weed control almost always requires a site be treated more than once and usually in combination with a large dose of elbow grease. Expect, too, that certain weed species are just darn hard to kill with the products available (consider speedwell or creeping buttercup in turf). We also tend to think that mechanical control alone will solve all our weed problems, and we fail to correctly estimate how many hours of hand-pulling and cultivation will be required to control species such as Canada thistle or field horsetail or common groundsel\u2014one or two times of weeding in the spring will not do the trick.<\/p>\n\n\n\n<p>Finally, it is also important not to give up the cause before the battle is truly over. Remember that weed problems do not crop up overnight\u2014neither will they be solved immediately. But they can be solved. Armed with a sensible plan, proper tools, and a large helping of persistence coupled with a good attitude, anyone can effectively manage weeds in nearly every situation.<\/p>\n\n\n\n<h2 class=\"wp-block-heading  wsu-heading--style-marked\" id=\"ch19-resources-herbicides\">Resources on Herbicides<\/h2>\n\n\n\n<p>Check out the section Home Garden and Landscape Weed Management in the <a href=\"https:\/\/pnwhandbooks.org\/weed\" data-type=\"URL\" data-id=\"https:\/\/pnwhandbooks.org\/weed\" target=\"_blank\" rel=\"noreferrer noopener\">PNW Weed Management Handbook (opens in new window)<\/a> for additional information on the use of herbicides. More herbicide and other pesticide information can be found on the <a href=\"http:\/\/npic.orst.edu\/\" data-type=\"URL\" data-id=\"http:\/\/npic.orst.edu\/\" target=\"_blank\" rel=\"noreferrer noopener\">National Pesticide Information Center (opens in new window)<\/a> website or at the <a href=\"https:\/\/www.epa.gov\/pesticides\" data-type=\"URL\" data-id=\"https:\/\/www.epa.gov\/pesticides\" target=\"_blank\" rel=\"noreferrer noopener\">US EPA website on pesticides (opens in new window)<\/a>.<\/p>\n\n\n\n<p>Registered products and formulations change from year to year, so it is important to know the current status of any herbicide you are considering. Remember, you must read, understand, and follow all label instructions of the product. The label is a legal document, and thus, the label is the law.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\" \/>\n\n\n\n<h2 class=\"wp-block-heading  wsu-heading--style-marked\" id=\"ch19-further-reading\">Further Reading<\/h2>\n\n\n\n<p><a rel=\"noreferrer noopener\" href=\"https:\/\/pubs.extension.wsu.edu\/\" data-type=\"URL\" data-id=\"https:\/\/pubs.extension.wsu.edu\/\" target=\"_blank\"><em>WSU Extension publications<\/em> (opens in new window)<\/a>.<\/p>\n\n\n\n<p>Approved common and chemical names of herbicides, and approved common and scientific names of weeds. <a href=\"http:\/\/www.wssa.net\/\" data-type=\"URL\" data-id=\"http:\/\/www.wssa.net\/\" target=\"_blank\" rel=\"noreferrer noopener\">Weed Science Society of America (opens in new window)<\/a>.<\/p>\n\n\n\n<p>DiTomaso, J.M., and E.A. Healy. 2003. Aquatic and Riparian Weeds of the West. ANR Publication 3421. University of California Agriculture and Natural Resources.<\/p>\n\n\n\n<p>DiTomaso, J.M., and E.A. Healy. 2007. Weeds of California and Other Western States, vol. 1 and 2. Publication 3488. University of California Agriculture and Natural Resources.<\/p>\n\n\n\n<p><a href=\"https:\/\/www.nwcb.wa.gov\/gardenwise-online\" data-type=\"URL\" data-id=\"http:\/\/www.nwcb.wa.gov\/nwcb_publications.htm\">Garden Wise (opens in new window)<\/a>. A guide to non-invasive choices for landscaping in Washington, eastern and western editions.<\/p>\n\n\n\n<p>Mallory-Smith, C., A. Hulting, D. Thill, D. Morishita, and J. Krentz. 2007. <a rel=\"noreferrer noopener\" href=\"http:\/\/www.cals.uidaho.edu\/edComm\/pdf\/PNW\/PNW0437.pdf\" target=\"_blank\">Herbicide-Resistant Weeds and Their Management (opens in new window)<\/a>. Pacific Northwest Extension Publication PNW437. University of Idaho.<\/p>\n\n\n\n<p>Noxious Weeds: Everyone\u2019s Enemy. 2006. DVD0002.<\/p>\n\n\n\n<p>Old, R.R. 2014. <a rel=\"noreferrer noopener\" href=\"http:\/\/xidservices.com\/\" target=\"_blank\">1,225 Weeds of the 48 States and Adjacent Canada<\/a><a href=\"http:\/\/xidservices.com\/\"> (opens in new window)<\/a>, DVD. XID Services, Inc.<\/p>\n\n\n\n<p><a href=\"https:\/\/pnwhandbooks.org\/weed\" target=\"_blank\" rel=\"noreferrer noopener\">Pacific Northwest Weed Management Handbook (opens in new window)<\/a>. 2021 (updated annually). Oregon State University.<\/p>\n\n\n\n<p>Pojar, J., and A. MacKinnon. 2004. Plants of the Pacific Northwest Coast, 2nd ed. Lone Pine Publishing.<\/p>\n\n\n\n<p>Prather, T., S. Robins, and D. Morishita. 2010. Idaho\u2019s Noxious Weeds, 5th ed. <em>University of Idaho Extension Bulletin<\/em> 816. University of Idaho.<\/p>\n\n\n\n<p>Prather, T.S., T.W. Miller, and S.S. Robbins. 2009. <a href=\"https:\/\/extension.oregonstate.edu\/catalog\/pub\/pnw-610-knotweed-shrub-complex-identification-biology-management\" target=\"_blank\" rel=\"noreferrer noopener\">Knotweed Shrubs: Identification, Biology, and Management (opens in new window)<\/a>. Pacific Northwest Extension Publication PNW610. University of Idaho.<\/p>\n\n\n\n<p>Taylor, R.J. 1990. Northwest Weeds: The Ugly and Beautiful Villains of Fields, Gardens, and Roadsides. Mountain Press.<\/p>\n\n\n\n<p><a href=\"http:\/\/plants.usda.gov\/\" target=\"_blank\" rel=\"noreferrer noopener\">USDA PLANTS Database (opens in new window)<\/a>. Plant taxonomic database from the Natural Resources Conservation Service. Search for invasive and noxious weeds by state.<\/p>\n\n\n\n<p>VanVleet, S. 2009. <a href=\"https:\/\/pubs.extension.wsu.edu\/invasive-weeds-of-eastern-washington\" target=\"_blank\" rel=\"noreferrer noopener\">Invasive Weeds of Eastern Washington (opens in new window)<\/a>. <em>Washington State University Extension Publication<\/em> EM005. Washington State University.<\/p>\n\n\n\n<p><a href=\"https:\/\/www.nwcb.wa.gov\/\" target=\"_blank\" rel=\"noreferrer noopener\">Washington State Noxious Weed Control Board (opens in new window)<\/a>. See webpage for current noxious weed lists, as well as for weed identification tools and noxious weed publications.<\/p>\n\n\n\n<p>Weeds Gone Wild. U.S. National Park Service.<\/p>\n\n\n\n<p>Weed Identification and Weed Management Techniques. 2001. DVD0086.<\/p>\n\n\n\n<p>Whitson, T.D., L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, and R. Parker, eds. 2009. Weeds of the West, 10th ed. Western Society of Weed Science.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Tim Miller, Extension Weed Scientist, Washington State University All photos in this chapter are the work of the author. Introduction Few would argue that weeds (such as the \u201cthorns and thistles\u201d above) have been a plague for humanity for a long time! In fact, ever since the advent of agriculture some 10,000 years ago, weeds [&hellip;]<\/p>\n","protected":false},"author":241,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_wsuwp_accessibility_report":null},"categories":[],"tags":[],"_links":{"self":[{"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/pages\/1513"}],"collection":[{"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/users\/241"}],"replies":[{"embeddable":true,"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/comments?post=1513"}],"version-history":[{"count":72,"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/pages\/1513\/revisions"}],"predecessor-version":[{"id":4839,"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/pages\/1513\/revisions\/4839"}],"wp:attachment":[{"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/media?parent=1513"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/categories?post=1513"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/extension.wsu.edu\/pnw-gardeners-handbook\/wp-json\/wp\/v2\/tags?post=1513"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}