Staying a Step Ahead of Invasive Weeds in Pasture

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Staying a Step Ahead of Invasive Weeds in Pasture

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About 27% of the US (528 million acres) is designated as pasture, which is land that provides forage for grazing livestock.  The vegetation in pastures consists of grasses, legumes, forb, and shrubs which usually grow in mixtures.

The importance of pasture

  • Forage for beef cattle, dairy cattle, sheep, goats, horses, and other domestic livestock.
  • Many species of livestock, ranging from big game such as elk to nesting birds such as meadowlarks depend on pasture for food and protection from predators.

The value of pasture

  • Pasture production is primarily measured in terms of livestock production.
  • Ecosystem services such as clean water.
  • Wildlife and fish habitat.
  • Recreational opportunities.

What are the major challenges to pasture?

Anything that affects the quality and quantity of available forage will impact the amount of food available to the livestock we depend upon or our livelihoods. For pasture, the major challenge is an infestation of weeds, some of which may be classified asnoxious or invasive weeds.

  • Aweed is a plant that is objectionable and interferes with the activities or welfare of man.
  • Anoxious weed is a plant regulated or identified by law as being undesirable, troublesome, and difficult to control.
  • An invasive weed is a plant that can establish, persist, and spread widely in ecosystems outside the plant’s native range.

Unlike cropland where weed management is intensive and results are more predictable, weed control in pasture is more difficult. Furthermore, grazing by livestock and wildlife can put a lot of pressure on forage resources often leading to overgrazing. Overgrazed pasture creates an ideal habitat for invasive weeds.

  • Presently, over 300 weed species have been identified as weeds of pasture. These weeds are estimated to cause losses of $2 billion annually to the United States economy.
  • Among the weed species that can invade pasture are some of the most problematic, and often are invasiveweeds. For example, cheatgrass (Bromus tectorum), leafy spurge (Euphorbia esula), and yellow star-thistle (Centaurea solstitialis).


What happens when weeds invade pasture?

Invasive weeds impact the livestock industry by:

  • Increasing costs of managing and producing livestock.
  • Lowering yield and quality of forage.
  • Reducing land value.
  • Interfering with grazing.
  • Reducing plant and animal diversity.
  • Poisoning animals.
  • Negatively impacting wildlife habitat and forage.
  • Depleting soil and water resources.


How can you control pasture and range weeds with herbicide?

Use the following steps:

  1. Scout fields
    1. Involves routinely walking or driving through the pasture to identify an invasive weed issue. Scouting helps define the scope of the problem which then informs management decision-making.
    2. While scouting, properly identifying the problematic weed species is a crucial first step.
    3. Correct weed identification is critical and weed species identification guides are available online from land grant universities or U.S. Department of Agriculture websites.
    4. Misidentification can be costly from the standpoint of the herbicide being ineffective and the forage yield and quality being compromised.


  1. Understand the invasive weed
    1. Characterize the biology and ecology of the invasive plant species.
    2. Knowing the life cycle traits and habits of a weed species is key to identifying vulnerabilities that can be exploited for good management.


  1. Select the herbicides to apply– base your selection upon:
    1. The forage species being grown.
    2. The weed species present.
    3. Application method.
    4. Environmental impact.

Read the pesticide label to ensure that the herbicide you select is safe to apply onpasture.

  1. Herbicide application technique

Herbicides can be applied either as preemergence or postemergence treatments.

    1. Preemergence treatments – though rarely used in a pasture, it involves the application of herbicides before weeds germinate and emerge. An understanding of the biology and ecology of the weed species is important when using pre-emergence herbicides.


    1. Postemergence treatments – application of herbicides made after weeds have emerged. Knowledge of weed life cycle characteristics is essential for maximum efficacy. Furthermore, postemergence herbicides may be applied as either broadcast or spot treatments.  
  1. Broadcast treatments – where herbicide is applied over the entire pastureland or rangeland that has the weed infestation.
  2. Spot treatments – if the invasive weed is localized and not widespread, spot treatments, as opposed to a broadcast application, may be the best technique to use that will also be less costly.


    1. Use of an adjuvant –when applying herbicides as postemergence treatments, adding an adjuvant to your spray mixture can enhance the activity of the herbicide and/or modify its physical properties. For example:
  1. Nonionic surfactant – reduces the surface tension of spray droplets which improves the wetting of plant foliage and increases herbicide uptake. In addition, nonionic surfactants help break down waxy cuticles of leaf surfaces which enables more effective herbicide uptake for improved control. For example:


  1. Water conditioning agent – to be used if you think your water source might compromise herbicide activity. A water conditioning agent can buffer the pH of the water, chelate iron, sequester hard minerals like calcium and magnesium salts, and promote the wetting of foliage and the uptake of the herbicide. For example:


  • Drift control agent – to be used if environmental conditions may cause spray to go off-target and cause unintended damage elsewhere. For example:


  1. Defoaming agent – to be used if you anticipate the development of foam in the spray tank that might compromise herbicide efficacy. For example:


    1. Evaluate control efficacy – evaluate how effective your control measure two to four few weeks following application and repeat applications if needed, and if possible.


Further reading



  • Ditomasso J.M. 2000. Invasive Weeds in Rangelands: Species, Impacts, and Management. Weed Sci. 48(2): 255-265
  • Weed Science Society of America. WSSA Glossary: Terms and Definitions. (Accessed, Oct.4, 2022)

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