Invasive annual grasses are among the most common and damaging threats facing western rangelands. Cheatgrass, also known as downy brome (Bromus tectorum), may be the most recognized, but it is not the only species land managers need to watch. Medusahead, ventenata, and other invasive annual grasses can reduce desirable forage, displace native perennial grasses and forbs, and alter the way water, nutrients, and fire move across the landscape.
These grasses are successful because they grow quickly, reproduce efficiently, and take advantage of seasonal moisture before many desirable perennial species become active. When annual grasses mature and dry, they can form continuous layers of fine fuel that increase the likelihood of fast-moving wildfire. This annual grass and wildfire cycle can make it increasingly difficult for sagebrush, native bunchgrasses, and other desirable vegetation to recover.
Annual Grass Control Requires More Than a Cheatgrass Plan
Although cheatgrass often receives the most attention, an effective management program should address the entire invasive annual grass complex.
Common annual grass threats include:
- Cheatgrass or downy brome, which germinates primarily in the fall, develops rapidly, and may dominate disturbed or weakened plant communities
- Medusahead, which produces persistent, silica-rich litter and sharp awns that reduce forage value and interfere with the establishment of desirable plants
- Ventenata, an expanding invasive annual grass that can invade rangelands, pastures, and areas with seasonally wet soils
These species do not behave identically. Their emergence timing, habitat preferences, maturity dates, and response to treatment can vary. Accurate identification is therefore the first step in choosing the appropriate treatment and application window.
Why are invasive annual grasses so competitive?
Many invasive annual grasses germinate in late summer or fall when moisture becomes available. Seedlings may remain active through mild winter conditions and resume rapid growth early in the spring.
This early start allows annual grasses to capture moisture and nutrients before desirable warm-season plants, and many native perennials, become fully active. Their shallow, fibrous root systems are especially effective at using moisture near the soil surface.
Several additional traits contribute to their success:
- Rapid emergence and early-season growth
- Prolific seed production
- The ability to establish on disturbed or sparsely vegetated ground
- Seedbanks that can persist across multiple growing seasons
- Earlier maturity than many desirable perennial grasses
- Dense stands that limit light, moisture, and growing space for other plants
Cheatgrass seed can persist in the soil for several years, which is one reason a single treatment rarely provides a complete solution. Successful control generally requires multiple years of monitoring, follow-up treatment, and management practices that help desirable vegetation occupy the space created by annual grass suppression.
The Annual Grass and Wildfire Cycle
Invasive annual grasses can fill the spaces between perennial plants with a continuous layer of vegetation. By late spring or summer, that vegetation becomes dry, highly combustible fuel.
Following a fire, annual grasses often establish more quickly than slower-growing perennial grasses and shrubs. As annual grass cover increases, the landscape may become more likely to burn again before native plants have fully recovered.
Historic fire intervals varied widely among sagebrush communities, ranging from decades in some cooler and wetter systems to much longer intervals in warmer and drier systems. Invasive annual grasses disrupt those natural patterns by increasing fuel continuity and creating conditions that support more frequent and extensive fire.
Building an Integrated Annual Grass Management Program
No single practice is appropriate for every infestation. Effective annual grass control combines plant identification, site evaluation, properly timed treatments, and long-term restoration goals.
1. Scout and Map Infestations
Begin by identifying the annual grass species present and documenting the size and density of the infestation.
Prioritize:
Early detection and rapid response are typically more practical and economical than attempting to restore a landscape after annual grasses have formed a continuous monoculture.
2. Protect Desirable Perennial Vegetation
Healthy perennial grass is one of the strongest long-term defenses against annual grass invasion. Management decisions should preserve existing desirable plants whenever possible.
Avoid practices that unnecessarily disturb the soil, remove perennial cover, or create large areas of bare ground. Where desirable vegetation is limited, annual grass treatment may need to be followed by reseeding or another restoration practice.
Treatment plans should be based on the site’s soil, precipitation, existing plant community, grazing use, and potential for successful revegetation.
3. Use Targeted Grazing Carefully
Cheatgrass and some other annual grasses can provide nutritious forage while they are young and actively growing. Properly timed grazing before seedhead development may reduce biomass and seed production.
Timing is critical. Once plants mature and awns harden, forage quality declines and sharp seed structures may injure the eyes, mouths, or skin of livestock.
Targeted grazing must also be managed carefully to avoid excessive use of desirable perennial grasses. Stocking density, grazing duration, plant growth stage, soil conditions, and recovery periods should all be considered.
4. Consider Mechanical Control for Smaller Areas
Mowing, hand removal, tillage, or other mechanical methods may help reduce seed production in small, accessible infestations.
Mechanical treatment should occur before viable seed is produced. However, mowing may be impractical on large, rocky or uneven terrain, and tillage can disturb the soil, expose buried seeds, and create new opportunities for invasive plants.
Equipment should be cleaned before moving to unexposed areas to prevent seed transport.
5. Time Herbicide Applications to the Annual Grass Life Cycle
Herbicides are often the most practical option for treating annual grasses across large or difficult-to-access rangeland acres. Results depend on selecting the correct product, rate, application timing, and treatment objective.
Depending on the product and target species, annual grass applications may be made:
The best application window is determined by soil moisture, soil temperature, rainfall patterns, plant development, desirable vegetation, and the product label. A calendar date alone should not be used to determine treatment timing.
Preemergence products also require adequate moisture to move the herbicide into the germination zone. Applications made to dry soil without timely rainfall may provide inconsistent results.
Alligare Solutions for Annual Grass Management
Alligare offers herbicide options that can be incorporated into an integrated program for cheatgrass, medusahead, and other labeled annual grasses.
Panoramic 2SL contains imazapic and is labeled for use on pasture, rangeland, Conservation Reserve Program land, and specified noncrop areas. It provides preemergence and early postemergence activity on labeled annual and perennial grasses and broadleaf weeds. Labeled annual grass targets include cheatgrass, medusahead, and other susceptible species.
For rangeland cheatgrass management, the Panoramic 2SL label recommends late-summer or fall applications before cheatgrass emergence when preparing a site for desirable vegetation establishment. Soil moisture is important for optimum residual activity and control of germinating weeds.
The appropriate rate depends on the target species, application timing, treatment objective, desirable grass species, and whether vegetation is established or newly seeded. Always consult the current product label and an Alligare representative before developing a treatment recommendation.
Panoramic 2SL is not registered in California.
Laramie® 25DF
Laramie 25DF contains rimsulfuron and is formulated for selective and nonselective weed control, invasive species management, and rangeland restoration west of the Mississippi River. It provides preemergence and early postemergence activity on cheatgrass, medusahead, and other labeled annual grasses.
Laramie 25DF may temporarily discolor desirable perennial grasses at the maximum rate, and the rangeland restoration section includes a 30-day grazing and forage restriction following treatment. Applicators should review the complete label, including use-site, seeding, grazing, application, and environmental restrictions.
Unlike Panoramic 2SL, Laramie 25DF is currently registered in California.
Use Adjuvants According to the Label
Adjuvant requirements differ by product and application timing.
For postemergence treatments, use the adjuvant type and rate specified by the herbicide label. Depending on the product and site, this may include a nonionic surfactant, methylated seed oil, or crop oil concentrate.
Adjuvant selection can influence weed control and desirable plant injury. Extra caution is necessary around newly emerged grasses, wildflowers, restoration seedings, and other sensitive vegetation.
Plan for Resistance and Follow-Up Control
Panoramic 2SL and Laramie 25DF are both Group 2 herbicides. Repeated reliance on the same herbicide group can select for resistant plants and reduce long-term performance.
A resistance management program should include:
- Accurate identification of the target grass
- Scouting before and after treatment
- Preventing surviving plants from producing seed
- Incorporating grazing, mechanical, cultural, or restoration practices
- Using labeled tank mixes or sequential treatments with effective alternative modes of action when appropriate
- Following all reseeding and plant-back restrictions
When combining products, every herbicide must be registered for the use site and target species. Follow the most restrictive directions, precautions, and limitations of all products in the mixture.
A Better Spring Starts with Fall Treatment
Fall provides an important opportunity to interrupt the annual grass life cycle before invasive plants dominate the next growing season.
A properly designed annual grass management program can help land managers:
- Reduce annual grass emergence and seed production
- Protect desirable perennial grasses and forbs
- Limit the buildup of dry, continuous fine fuels
- Preserve forage availability and grazing efficiency
- Improve the success of future restoration efforts
- Increase the resilience of rangeland plant communities
The most successful programs do more than Control existing plants. They reduce future seed production, protect desirable vegetation, address reinvasion, and create conditions that allow productive perennial plant communities to recover.
Plan now, treat at the correct growth stage, and continue monitoring after the initial application. Proactive annual grass control today can help protect forage, wildlife habitat, grazing operations, and rangeland resources for seasons to come.
To develop an annual grass management program for your property, visit Alligare.com or use Find Your Ally to connect with your local Alligare Range & Pasture specialist.
Always read and follow all federal and state product label directions. Product registrations, rates, restrictions, and approved use sites may vary by state.
Cover photo by Jennifer Strickland, U.S. Fish and Wildlife Service.
