Invasive annual grasses have become problematic across the Western region because they readily outcompete more desirable perennial grasses, especially in areas that have been recently burned or where the soil and vegetation have been disturbed. Without intervention, these dominating annual grasses can grow several feet tall and become a persisting fuel for wildfire.
Grazing can be an effective tool for reduction and control of invasive annual grasses, including cheatgrass and medusahead, if managed with that as the objective. Strategic livestock grazing can decrease growth and spread of invasive annual grasses, provide opportunity for perennial plant establishment and reduce fuel loads for wildfires.
Timing of grazing
Annual grasses are most vulnerable to grazing when they are green as seedlings and during early leaf growth, which occurs between germination (usually late fall) and flowering and seed production (usually mid- to late spring). The optimal time of grazing to reduce annual grasses coincides with the time of year that the perennial grasses are usually dormant, therefore providing a window of opportunity.
Late fall and winter grazing is an effective way to decrease biomass to decrease fuel loads for wildfire, which decreases fire risk the following year. In the spring, the growing annual grasses are green, palatable and more vulnerable to grazing pressure, and the dormant perennial grasses will be less palatable to livestock and will not be as susceptible to impacts of intensive grazing.
Because growing season varies so much by geographical location and climate, it is important to judge the best timing for grazing based on the stage of growth of both annual grasses and perennial grasses. As soon as the perennial grasses begin to green up, continuing to graze intensively will stress both annual and perennial grasses, and eventually have greater impact on the desired perennial plants.
Grazing strategy and frequency
The best strategy for grazing to reduce invasive annual grasses is to graze intensively with high-density stocking rates over a short period of time. The objective is to remove as much of the annual grass biomass throughout the winter and in the spring while it is green, before flowering and seed production. Furthermore, annual grasses should be intensively grazed repeatedly to induce as much stress on the growing plants as possible. Fortunately, annual grasses are most palatable and hold the most nutritive value when they are green in the spring.
Cheatgrass, for example, has been reported to provide 15% crude protein (CP) in early May, and growing livestock gain well while grazing green cheatgrass. Medusahead has a smaller window of palatability for livestock, which has been suggested to only last for a few weeks prior to flowering. Furthermore, cattle have been reported to maintain and even improve body condition when grazed on pastures of mostly cheatgrass in late fall when supplemented with protein. Targeted grazing to control annual grasses should be applied for two or more years for best results.
Optimal grazing strategy to reduce invasive annual grasses
1. Graze intensively and repeatedly in the late fall after perennial grasses have gone dormant and annual grasses have germinated and started growing.
Objective: Remove biomass and induce stress
2. Intensively and repeatedly graze invasive annual grasses in the early spring as they begin to grow back, but only while perennial grasses are dormant.
Objective: Remove biomass and prevent flowering and seed production
3. Once the perennial grasses start to green up and grow, do not graze until they have matured (about 10 inches grass height is a good rule of thumb), and then only graze lightly during the growing season.
Objective: Establish perennial grasses
4. Graze to target invasive annual grasses for at least two to three years.
Objective: Control or eradicate invasive annual grasses
5. Use other management tools in addition to grazing, including herbicides, controlled burning and mechanical removal.
Objective: Gain control over invasive annual grasses more quickly and effectively
Targeted grazing is one of the most effective tools when battling invasive annual grasses. When carefully managed with the objective of reducing or eliminating these invasive species, intensive grazing can provide positive results in only a few years. Grazing can also be used in conjunction with other management strategies applied prior to seed production to speed up the process, including herbicides, controlled burning and mechanical removal.
