Weeds and Invasive Plants

A threat to your woodland

Invasive weeds hamper forest health more than you might think – they often threaten the re-growth of trees, damage wildlife habitat, reduce crop yields and even increase fire danger.  Most invasive weeds come from outside of North America and thrive here because they are free of the insects, diseases, and animals that control them in their native lands.  Common invasive weeds – also called noxious weeds - include Scotch and other brooms, English ivy, various thistles, knapweeds, knotweeds, and many others.                                                                                                                           

We have provided fact sheets and other resources to help you manage invasive weed problems.   Included is information about invasive weed identification, how to control invasive weed infestations, and how to prevent them from becoming established in the first place.

WEEDY RESOURCES TO GET YOU STARTED:

Oregon - Noxious Weed Information

The Oregon Department of Agriculture manages Oregon’s noxious weed control program including the state’s official list of noxious weeds and noxious weed profiles including photos, descriptions, and information about weed impacts.   Noxious weeds are just one category of invasive species -    learn about other invasives ranging from exotic diseases to feral swine from the Oregon Invasive Species Council.  

 Identification Guides

Pocket-sized weed identification guides are available through the Institute of Applied Ecology.  There are guides for the Willamette valley, eastern Oregon, and the Oregon coast.  You can view them online or order hard copies.  The USDA Forest Service’s Nonnative Invasive Plants of Pacific Coast Forests-A Field Guide for Identification includes range maps, pictures, and detailed descriptions of several dozen invasive weeds (note: weed descriptions are somewhat technical).  

Invasive Weeds in Forest Land

These fact sheets from the Oregon State University Extension Service provide photos, descriptions, and management options for controlling common invasive weeds in forest lands throughout the Pacific Northwest.

• Bull thistle
• Butterfly bush
• Canada thistle
• Slender false brome
• Garlic mustard
• Gorse
• Armenian (Himalayan) & Evergreen blackberry
• English ivy
• Knapweeds
• Knapweeds in Central & Eastern Oregon
• Knotweeds
• Scotch broom
• Other brooms
• Tansy ragwort
• Yellow starthistle

A word about poison oak: You may be surprised to learn that poison oak is not considered a noxious weed, at least officially.  The reason is that it’s a native plant that does have many of the negative effects of non-native, invasive plants.  But it’s still considered an (ob)noxious weed by many.   Poison oak and poison ivy information.

OSU Extension publishes a 43-page guide ($5, can be previewed online) to Pacific Northwest’s Least Wanted List: Invasive Weed Identification and Management, including photos and information about life cycles, identification, origin, impact, habitat and ecology, and management.  

Want more information about weed control methods?  A general reference for weed control is the Pacific Northwest Weed Management Handbook.  The Nature Conservancy’s Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas provides detailed information about weed control techniques including manual and mechanical methods, grazing, prescribed fire, biological control, and herbicides.  

Prevention

This short article by the Nature Conservancy describes six easy, common-sense ways you can prevent invasive species.  

Early Detection, Rapid Response (EDRR) is the key to invasive weed prevention.