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Weeds

Photo Credit: Jamie Street - Unsplash.com (Cropped from original)
Description:

Weeds are considered the #1 pest in agroecosystems. They compete with desirable plants and can reduce yields, and alter soil structure and quality. Weed management requires thoughtful planning and action. Use the resources below to help reduce the effect of weeds in your crop, garden, pasture or landscape.

PNW Weed Management Handbook

This comprehensive guide to weed management in the Pacific Northwest covers biological weed control agents; pesticide safety and disposal; agrichemicals and their properties; and control of problem weeds.

Search the handbook

Photos: Judit Barroso, © Oregon State University (Cropped from original)

Featured resources

Tracking weeds is first step in controlling them

When winter approaches, it’s time to check your weed control plans. Noxious weeds are best controlled if you track them carefully. Weed mapping and weed calendaring are two activities important to tracking weeds so that you can properly control them. Here are a few tips to get you started.

Shelby Filley | Dec 2025 | OSU Extension Catalog Peer reviewed (Gray level)

How to use herbicides to safely control weeds on farms

Herbicides can be a useful part of an integrated weed management program for farms. But selecting and applying the appropriate herbicides can be challenging. Here are the key things to consider.

Evie Smith | Dec 2025 | OSU Extension Catalog Peer reviewed (Gray level)

Are your weed-control products damaging nearby vineyards?

People living near a vineyard can learn to understand the damaging effects that common herbicides can have on grapevines. Learn how these products cause damage and how to minimize spray drift and grapevine damage.

Patricia A. Skinkis | Feb 2025 | OSU Extension Catalog Peer reviewed (Orange level)

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Having weed problems?

Solve Pest Problems is a partnership between OSU and Oregon stakeholders to provide a user-friendly online resource to help urban and rural property managers to solve pest problems. Learn research-based, safe, and effective tactics for common garden and property pests and weeds. We provide non-chemical methods alongside the most effective and least toxic chemical options available, to reduce risk to people and the environment.

Learn more

Common weeds

Tansy ragwort

Tansy ragwort, an invasive weed that can harm certain types of livestock, is making a comeback in western Oregon. Find out how to control it and protect your animals.

Shelby Filley, Andy Hulting, Gene Pirelli, Eric Coombs | Jul 2024 | OSU Extension Catalog Peer reviewed (Gray level)

How to remove poison oak plants and treat a rash

Poison oak plants contain a chemical that causes a severe rash. Learn how to spot a plant, safely remove, and clean your clothes, gear and skin afterward to prevent a rash.

Lauren Grand | Jan 2025 | OSU Extension Catalog Peer reviewed (Gray level)

Russian Thistle: Management in a Wheat-Fallow Crop Rotation

Reviews Russian thistle biology as it relates to management, including seed dormancy and longevity in soil, seed distribution, seed germination and emergence, plant growth after establishment, crop competition, and ...

Judit Barroso, Drew J. Lyon, Timothy S. Prather | Aug 2023 | OSU Extension Catalog Peer reviewed (Orange level)

More weed guides for specific crops

Best Management Practices for Managing Herbicide Resistance

Learn to manage herbicide-resistant weeds on your farm using the most effective methods, also known as best management practices (BMPs).

View the guide

Photo Credit: Marcel Poncu - Adobe Stock (Cropped from original)

Latest resources

How can I control or eliminate Italian arum in my yard?

Q: I live in Portland and recently bought my first home. I’m starting a native garden, but under a cedar tree there is a 40-square-foot patch of Italian arum. I have tried digging some out, but the roots are very deep. ...

A: View answer | View all featured questions

Bristly hawksbeard ID guide

Bristly hawksbeard is a common weed in Western Oregon and Washington. The fast-growing annual bears bright yellow flowers. Stems have fine, soft hairs.

Renan N.D. Favera, Carol Mallory-Smith, Victor Hugo Vidal Ribeiro | Dec 2025 | OSU Extension Catalog Peer reviewed (Orange level)

Dandelions: Living with, or without, them

Bright yellow dandelions (Taraxacum officinale) are a common sight in lawns and gardens across Oregon, mostly in undisturbed areas. Whether you love them or want to get rid of them, it helps to know more about dandelions—how they grow, what good they can do, and how to manage them if needed.

LeAnn Locher, Srijana Shrestha | Apr 2025 | OSU Extension Catalog Peer reviewed (Gray level)

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Latest news

OSU survey guides weed strategy for vegetable seed production

Findings help focus research, reduce risk and strengthen growers.

Aaron Becerra-Alvarez | Mar 2026 | Impact story

OSU survey highlights weed challenges in Oregon agriculture

The statewide assessment provides the roadmap to target research, testing and Extension education where they will deliver the greatest benefit.

Victor Hugo Vidal Ribeiro | Oct 2025 | Impact story

Oregon State research helps wheat growers manage glyphosate-resistant Russian thistle

By advancing effective alternatives to glyphosate and promoting integrated management, Oregon State is helping protect the productivity and sustainability of Oregon’s wheat industry.

Larry Lutcher, Judit Barroso | Oct 2025 | Impact story

All news

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Upcoming Events

May 2

Weed ID Walk

11:30 am - 12:30 pm Eugene, OR
May 9

Spring Weed Watchers Workshop

10:30 am - 12:00 pm Corvallis, OR
Jun 6

Weed ID Walk

11:30 am - 12:30 pm Eugene, OR
See All Events

Meet Our Experts

Judit Barroso
Weed Science
Marcelo Moretti
Associate Professor

Contact me with questions about weed management in commercial agriculture.

Aaron Becerra-Alvarez
Assistant Professor

Weed science in vegetables and specialty seed crops

Victor Ribeiro, OSU Extension Weed Specialist
Victor Hugo Vidal Ribeiro
Assistant Professor, Extension Specialist in Weed Science
See All Weeds Experts
Ask Extension

Have a question? Ask Extension!

Ask Extension is a way for you to get answers from the Oregon State University Extension Service. We have experts in family and health, community development, food and agriculture, coastal issues, forestry, programs for young people, and gardening.

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What is the biological control of weeds?

Q: I have a lot of tansy ragwort and other weeds in my pasture. Is there bug I can use to help control it?

A: View answer | View all featured questions

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