Visit our Colorado State Extension office for more news, tools and resources.

Close Icon
Colorado Small Acreage Management - Improving land stewardship by helping landowners understand and manage their property resources (soil, water, animals, plants, and air).

Weeds   arrow

What are Weeds

What are weeds?

  • a plant out of place and not intentionally sown
  • a plant growing where it is not wanted
  • a plant whose virtues have not yet been discovered (R.W.Emerson)
  • plants that are competitive, persistent, and interfere negatively with human activity or management

We can say that weeds are plants whose undesirable qualities outweigh their good points. In the US, crop losses and weed control programs are in the tens of billions of dollars each year.

Weeds are naturally strong competitors and those weeds that can best compete always tend to dominate. We may breed plants for yield, while nature breeds plants for survival. (D. Ligenfelter)

Purple Loose Strife

Weeds are excellent competitors for resources. This photo shows purple loosestrife invasion into a dense wetland area.

What are noxious weeds?

Noxious weeds are non-native plants that disrupt native vegetation because they have no natural controls and are able to adapt to varied climate conditions. As a result of the Colorado Noxious Weed Act, noxious weeds have been categorized according to their status: A, B, and C.

List A Plants: Eliminated everywhere

List B Plants: Spread should be stopped

List C Plants: Control is recommended

Watch List: Early identification of potentially harmful plants

Pocket Guide

Noxious Weed Management Pocket Guide

Noxious Weed Management Pocket Guide

Easy to print and carry; provides information to identify and help manage some of the common weeds for Colorado. Click to download your area specific guide.


How can I control weeds on my property?

  1. Identify your weeds
    • Know exactly what it is you want to control.
    • Determine the species – use ID guides or consult your local professional
  2. Learn about the “ENEMY”
    • Know the weed’s life cycle
    • Determine the best time to attack the plants
  3. Understand control methods
    • Know preventative, cultural, mechanical, chemical, and biological
    control options.
    • Determine the appropriate control method for your specific weeds.
  4. Develop a management plan
    • Know how to monitor and evaluate your property
    • Determine how to treat your land, be persistent and adaptive

Musk Thistle Flower - Photo from the Department of Ag          Russian Knapweed - Photo from the Colorado Department of Ag

Determine the Appropriate Weed Control Method for your property

Effective control depends on persistence and an integrated approach utilizing a combination of all the available methods.

The first and the most important step in a weed control program. Probably the most cost-effective method of weed control. Methods include: maintaining healthy pastures, using weed-free crop seed, weed-free manure and hay, and clean harvesting and tillage equipment, as well as the elimination of weed infestations in areas bordering cropland, and in irrigation ditches and canals.

Methods include: Establishing and managing an adequate population of desirable vegetation to compete with the weeds; utilizing livestock (cattle, goats, sheep) when possible; mulching; burning; and even plastic weed barriers.

Methods include: Hand-pull, hoe, mow and tillage.

Tamarask BiocontrolBiological weed control involves the utilization of natural enemies for the control of specific weed species. Likely not 100% effective method of control, and can take many years for success. Methods include: grazing, introduction of registered insects or diseases. Contact the Palisade Insectory for more info.

Always read the label before using any herbicide! Weed control with herbicides is an effective tool for many target weed species. However, there are several aspects to consider when choosing a chemical program. These include: ID of target weed; herbicide selection; timing of application; desirable crops or plant species near control areas; the number of applications per year, and the number of years for treatment.

Always add a nonionic surfactant @ 0.32 oz/ gal (1qt/100 gal) unless otherwise noted.

Take a look at the Sprayer Calibration Fundamentals factsheet to ensure you are applying your herbicides appropriately.

Backpack sprayer          Backpack sprayer

    • Remember,


    • Always read and adhere to all instructions on the label.

Targeted Weed Control Using Livestock:


Resources & Helpful Information

Weeds of the West publication
Weeds of the West (pdf)

SAM Webinars and Web Videos

SAM Newsletter Articles

CSU Extension Fact Sheets