by Marguerite Kirby, Yakima Master Gardener
Researching and then making a presentation on ‘How to Eradicate Puncture Vine’ (Tribulus terrestris) was my final assignment before I became a WSU Yakima Master Gardener in 2024. I knew this herbaceous pest as Goathead, but it has many other names, such as Devil’s Weed, Caltrop, Cat’s-head, Tack weed, and others depending on the state where you live. I had exhaustive experience with this devil weed and spent thousands of dollars fighting it earlier on my property in the Wenas Valley.
It wasn’t there when I moved from the Westside in 2004. My neighbors, who homesteaded in the early 1900s, said it showed up only 7-8 years ago. In a short time, was growing up and down both sides of our long shared driveway.
While frequently found in rural areas, puncture vine can also be found often in urban settings, parks, fields and backyards.
My beautiful yard was still beautiful but now lined with the nasty, horrible, awful and painful sharp thorny spikes that would hurt like a giant wasp sting if stepped on. I never dared going barefoot outside, but those nasty thorns found their way inside my house on the bottom of my shoes. I stepped on several that buried themselves in my rugs. The tiny slivers are hard to remove from hands and feet. Puncture vine seeds easily embed themselves in hiking boots, tennis shoes, flip flops or work gloves. They are sharp enough to easily puncture tires on bikes, riding lawn mowers, and wheelbarrows.
Tribulus terrestris is toxic to livestock, particularly sheep, and is a Class B noxious weed in Washington State. Its sharp, woody burrs cause mechanical injuries to animal feet, mouths, and digestive tracts, while the foliage can cause poisoning and photosensitization. Be sure to keep house pets away from infested areas and check paws often.
According to Yakima County Noxious Weed Board, puncture vine is spreading mainly due to seeds being carried by vehicles, mowers, foot traffic and just falling off the vine. Researchers have found that seeds can be viable for 4-5 years, and possibly for as long as 50 years.
Puncture vine seeds will germinate when temperatures consistently reach 65-70 degrees. Most likely we will see them in Yakima by end of April or early May. Seedlings pop up after a good watering or rainfall.
Puncture vine is easy to identify. It grows like a flat mat. Tiny yellow flowers ¼” in diameter form quickly, and develop into 5-sided thorny spikes in approximately 10 days. Now imagine one plant that can produce up to 100,000 seeds if left over winter will germinate over the next several years! Don’t let them grow! Take them out when small and keep removing them until they are eliminated! It can be done!
The best way to eradicate puncture vine is to remove the plants before the flowers turn into thorny, sharp burrs, which are the seeds. Pluck plants out by hand-picking or mechanically hoeing or lightly tilling the soil. Just cut the center stem about 1” below the base to break off the tap root. Puncture vine is an annual, and that kills the plant. Getting them before they set seed is the key! Do the same with any size puncture vine plant. Just find the center tap root, break it off just below the ground. Put all plants in the trash, and never in your compost or yard waste.
If you are considering using an herbicide, you can use a pre-emergent early in the season. Glyphosate is an effective post-emergent herbicide, especially when applied to young, actively growing plants before they flower and set seed. According to Washington State Noxious Weed Control Board, it is best used as a spot treatment in non-turf areas like driveways. Be sure to read labels and follow directions on all chemical products. It’s critical to wear gloves and protective coverings when using herbicides. Absolutely do not spray next to ponds, irrigation channels, rivers, lakes or any standing wetlands as that could cause further damage to natural habitats in our delicate ecosystem.
The Yakima County Noxious Weed Board (509-574-2180) is an excellent resource for more information.
My personal eradication experience began the year before I took the WSU Master Gardener class. I dealt with an insane infestation of puncture vine along my driveway. I decided to take drastic measures. I brought in several truckloads of topsoil and covered the weeds by making a 3 foot-high, 60 foot-long berm. Then I covered the soil with 2 layers of thick black plastic and topped it off with 4 to 5 inches of chipped rock. I buried that puncture vine so deeply, never to see again! Or so, I thought!
That area did quite well, but a few plants made it over to other spaces on my property. Those darn seeds stick on the wheels of riding mowers and wheelbarrows and all types of shoes, then fall off in other areas. Last year I picked out hundreds of tiny plants on the opposite side of my driveway, a few in my lawn, and dozens growing in my neighbor’s pasture. I’m confident and determined that I will completely eradicate puncture vine on my property. Last year I made huge progress by frequent careful monitoring. Whenever I spot a plant, I hoe it out.
This year I see fewer weeds along my driveway and no puncture vine yet. Take my advice. Get out there early in the season and inspect areas a few times each week, especially after it warms up. Pull out those smaller plants before they go to seed. Be diligent to remove all plants with thorny seeds. After removal, add a thick layer of mulch over the soil to keep the weeds down.
If we all do our part, we can stop the spread of puncture vine. It’s a big task but just know you can win the battle just as I have done out in the Wenas Valley and other Master Gardeners have on their properties.