Cheatgrass Management – Frequently Asked QuestionsWritten by Brian Mealor
Many of the questions I receive from around the state the last few years have been related to managing one of the West’s worst invasive weeds, cheatgrass. It has been negatively affecting rangelands for many years, and its impacts were deemed almost beyond control as early as the 1940s. However, the individual landowner may be able to implement some control actions that will lead to very positive results.
Some Wyoming studies indicate an increase in perennial grass production up to six-fold upon the removal of cheatgrass from productive rangelands. This is not necessarily a net increase in forage production, since cheatgrass itself provides a grazing resource early in the year, but it is definitely an improvement on a number of levels. Since fall is an excellent time to work on cheatgrass control, we will discuss a few of the more prominent questions I have received regarding cheatgrass management in the past several years.
Can I control cheatgrass with herbicides?
As with many management issues, the answer to this question depends on the specifics of the situation. Questions that should also be asked when deciding on any treatment plan would include:
• Are there desirable plants on the site which can recover if cheatgrass is removed?
• If there are no desirable plant remaining in the area, can I plant desirable species from seed?
• Are those desirable plants susceptible to damage from the herbicide I plan to use?
• Do I have the ability to manage grazing so that perennial grasses have the opportunity to grow once cheatgrass is removed?
• How much time and money am I willing to invest into a cheatgrass control program, and what will the benefits be?
In much of Wyoming, cheatgrass will germinate and emerge in the fall if we receive sufficient moisture. It will then overwinter and be ready to grow early the next spring. It may also germinate in spring, even within the same areas where fall germination was observed. This ability to have multiple germination events in one calendar year makes controlling cheatgrass difficult with a single application of any herbicide without some ability to persist in the soil and affect newly germinating seeds. We often see the best results with fall application of such herbicides (Table 1). There are many different herbicide options labeled for controlling cheatgrass, or restoring desirable species in cheatgrass-infested rangelands (Table 1).
The most commonly used rangeland herbicide for cheatgrass control in Wyoming has been Plateau. It has demonstrated both good results and poor results, depending on the situation. Some generalizations regarding fall pre-emergent applications of many of the herbicides may be made. High amounts of cheatgrass litter, or dead plant material from previous growth, may reduce the effectiveness of preemergent herbicides. Not only is litter capable of intercepting the herbicide and preventing it from reaching the soil surface, but litter layers also facilitate the establishment of cheatgrass: a negative tradeoff for weed management. Fall pre-emergent applications may also reduce the injury to desirable perennial grasses, especially if those grasses are not actively growing at the time of application.
Can grazing be used to control cheatgrass in my pasture?
Using livestock as a tool to manage unwanted vegetation, or to meet vegetation goals, is a common practice. Cheatgrass can serve as a valuable forage source early in the spring when other plants have not begun to actively grow. The ability to use it as a resource while obtaining some control over the population is an attractive alternative to chemical control from both an economic and ecological standpoint… but will it work?
An Oregon State University study from 2008 provides some insight into potential effectiveness of grazing as a control for cheatgrass.
Researchers clipped plots of cheatgrass at two different heights (one and three inches), at two different growth stages (boot stage: when the plant is elongating its inflorescence, and purple stage: when cheatgrass has turned purple), and at two frequencies (once or twice during the growing season). The highest reduction in cheatgrass seed production was observed when plants were clipped short (about one inch) at the boot stage and again two weeks later. This treatment resulted in seed densities between 123 to 324 seeds per square meter at one site and 769 to 2,256 seeds per square meter at another site. The unclipped plots produced an average of approximately 13,000 to 20,000 seeds per square meter, meaning that simulated intensive utilization may be able to reduce cheatgrass seed production by up to 90 to 99 percent over one year. Although these results are impressive, the practicality of using grazing at these levels must be called into question.
If we assume we can reduce cheatgrass seed to 125 seeds per square meter, which equates to roughly 500,000 seeds per acre, or approximately two pounds of seed per acre… which would lead to plenty of cheatgrass plants the following year to compete for moisture and produce more seed if the grazing pressure is not maintained. However, is maintaining that level of grazing pressure a good idea? Good grazing management practices recommend against grazing the same area at the same time each year and grazing at a moderate (about 50 percent) utilization to maintain the vigor of desirable perennial grasses. One year of heavy spring grazing may not be detrimental to the condition of perennial grasses, but the negative impacts of repeated heavy spring use in a pasture would likely outweigh the benefit of cheatgrass population reduction. So, should we not consider grazing as one of the tools for cheatgrass control? A diplomatic answer to this question would be that it, like other weed control questions, is that it depends on the situation.
If you determine that your cheatgrass infestation is negatively affecting your property enough to warrant control, keep these things in mind while developing a management plan. Loss of vegetation diversity and productivity can significantly reduce your ability to manage your property for grazing and wildlife habitat. If you would like more information on developing a cheatgrass management strategy suited to your needs, consider attending an upcoming cheatgrass management workshop in Wheatland on Sept. 28. For more information on the workshop, contact Brian A. Mealor at the University of Wyoming or Jim Cotterman at Platte County Weed and Pest.