Invasive Plant Species

Program Contact: Paula Dinius, Urban Horticulturist
(509) 667-6540 • pdinius@wsu.edu

What is an Invasive Species?

An “invasive species” is defined as a species that is:
1) non-native (or alien) to the ecosystem under consideration and
2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health (Executive Order 13112).

Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions.

Many scientists believe the spread of exotic species is one of the most serious, yet least known threats to agriculture and biodiversity. Conservative estimates count 2,000 alien plant species that have established themselves in the United States, 350 of which experts say are serious and dangerous invaders. Non-native animal species cause $123 billion worth of damage each year to crops, range land and waterways, according to a report by the federal government.

How do they get here?

The ocean serves as a highway in transporting invasive species into U.S. waters. Every minute 40,000 gallons of foreign ballast water are dumped into U.S. harbors. This water contains a multitude of non-indigenous organisms that could alter or destroy America’s natural marine ecosystems, according to the National Oceanic and Atmospheric Administration.

Packaging material is a major transport channel for invasive species. I was contacted last week regarding “eggs” found in a cardboard box containing imported food products from Mexico. They turned out to be plant seeds. Imagine if the cardboard box had been put in the recycle bin outside, the seeds escaping rolling onto exposed ground. Just add water and the potential for another invasive plant species to be introduced into the U.S. is present.

Many invasive species began their rampage after escaping from ornamental landscapes. Many of these aggressive invaders are available at nurseries across the country. Even species that have been deemed noxious weeds are still available at nurseries, home improvement centers, and through the internet. Few people would purchase Dalmatian Toadflax, Baby’s Breath or Purple loosestrife for their garden knowing the problem these noxious weeds impose on the ecosystem in Central Washington. But what about the many invasive plant species that are not so well known. Do you have any in your landscape?

What can be done about it?

On a national scale, individuals from diverse fields have collaborated to draft voluntary Codes of Conduct for government agencies, nursery professionals (American Nursery & Landscape Association), landscape architects (American Society of Landscape Architects, botanic gardens and arboreta (American Association of Botanical Gardens and Arboreta), scientists (USDA Agricultural Research Service), conservationists (Center for Plant Conservation) and the gardening public. Through self-governance and self-regulation, these codes would encourage behaviors that detect and prevent future introductions of invasive ornamental species.

Here are some suggested ways that nursery professionals and the gardening public could participate in regional and national efforts to reduce the effect of invasive plants:

  • Phase out existing stocks of regionally invasive species.
  • Purchase and promote non-invasive, environmentally safe species.
  • Remove invasive species from your land and replace them with non-invasive species suited to site conditions and usage.
  • Work with neighbors or volunteers at botanical gardens and natural areas to eliminate populations of invasive plants.

*Voluntary Code of Conduct from Dr. Sarah Reichard, taken from Dr. Linda Chlker-Scott’s The Myth of Well-Behaved Ornamentals.

Learn more. . .

Washington State Noxious Weed Control Board
Biological Control

Washington State University