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Submodule 8: How Invasive Plants Are Controlled
Prescribed Grazing: A Biological Control Agent
(all photos courtesy Larry Howery)
Prescribed grazing, when used for weed management, uses livestock to:
- Reduce unwanted weeds so that native vegetation can regain a competitive advantage
- Reduce weeds prior to beginning a restoration or revegetation project
- Control weeds that provide fuel for fires in at-risk locations
Goats and sheep are the primary animals used to manage weed infestations, but cattle are also useful. The species of animal chosen depends on the target weed or weed species to be controlled. Generally, sheep prefer forbs and goats prefer woody plants, while cattle prefer grasses. Depending on how well animals are managed, grazing can either increase or decrease weed infestations. When animals are mismanaged, grazing can increase soil disturbance, transport weed seed, and reduce the ability of natives to out-compete invasive plants. On the other hand, properly managed prescribed grazing can reduce weed biomass, reduce weed seed availability, and provide spatial niches and temporal time spans for natives to reestablish.
Prescription grazing is designed to:
- Inflict maximum damage to the target weed without inflicting excessive damage to desired vegetation
- Be compatible with other methods of weed control in an integrated approach.
To increase your success in using animals for weed control, it is critical to:
- Use the correct grazing animals. Different animals have different grazing preferences. Match the appropriate livestock species with the targeted weed species.
- Graze at the appropriate time of the year
- Certain weeds and parts of weeds are palatable only during certain times of the year
- Time the grazing so it is most detrimental to the weed, such as when flowering begins so seeds are never set.
- Time grazing when it is most beneficial to native plants and allow native vegetation to recover between periods of grazing.
- Release the correct number of animals for an appropriate length of time.
- Overgrazing can actually increase the weed problem.
- Remember that all livestock, including goats, sheep, and cattle, can spread weed seeds in their digestive tracts. Feed weed free feed for up to five days before moving livestock to a weed-free area to avoid spreading weeds.
In some areas, there are businesses that lease grazing animals (particularly goats and sheep) for weed control. Prices can range form $20-$200/acre depending on the local operator and conditions such as location, accessibility, and type of land.
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