Managing Invasive Cool Season Grasses - October 19, 2005
Jeff Schalau, County Director, Associate Agent, Agriculture & Natural Resources
Arizona Cooperative Extension, Yavapai County
Non-native annual grasses are increasing across the western United States. In the mid-elevations of northern Arizona, non-native annual grasses are spreading rapidly and invading wildland ecosystems and finding their way into residential landscapes. Some species of concern in our area are: downy brome or cheatgrass (Bromus tectorum), red brome or foxtail chess (Bromus rubens), Japanese brome (Bromus japonicus), ripgut brome (Bromus rigidus), and wild oats (Avena fatua). Below, I discuss potential impacts of and management strategies for these invasive annual grasses.
Cool-season annual grasses often utilize fall precipitation to germinate, establish roots and some leaves during winter months, then accelerate growth and produce seeds in spring. However, if fall moisture is limiting, these species can germinate in the spring and produce seed in a very short time. Cool season annual grasses germinate rapidly if buried in one inch or less of mineral soil. The seeds will usually not emerge if buried at least four inches. In our area, these grasses often germinate following the monsoon season and can survive through most winter drought periods.
While the grasses mentioned above are not true “foxtails”, they do have barbed seeds that are readily transported by human and animal activity. The seeds can easily attach to people’s clothing, animal fur, off-road vehicles, mowers, tillers, and other equipment. This is one way they are transported to establish themselves in new areas. Pet owners are also acutely aware of the seed’s potential to become lodged in an animal’s nostrils, ears, and even penetrate the skin.
These grasses will also colonize areas following disturbance such as fire, flood, construction, poor grazing management, off-road vehicle use, and other human activities. Some of these species have been important fuels in major wildfires across the west including the Cave Creek Complex that burned 244,000 acres of north of Phoenix last summer. Once an area has burned, these non-native grasses often become denser and expand their range. Nevada’s Great Basin has also experienced large fires followed by rapid colonization of downy brome. Natural resource managers use the term “fire-adapted” to characterize this plant trait. Needless to say, these species should be controlled to reduce fire risk around homes and flammable structures (including fences, decks, and propane tanks).
While it is often difficult to control these non-native grasses on a large scale, it is relatively easy to control them in residential areas. Learning to recognize them may be the most difficult step. Cool season annual grasses are easily pulled for moist soil while perennials are nearly impossible to pull. Internet users can access pictures of the above listed species at the following web site: plants.usda.gov/index.html.
The best control method is prevention and rapid removal once detected. After these plants have produced seed on a site, you will likely need to control them for at least two years. Hand pulling or hoeing is very effective when done any time prior to the seeds maturing and the sooner the better. In garden or cropped areas, the plants can be tilled or disked under. Mowing is not a good solution as mowed plants can still produce seed.
Grazing animals will only feed on the annual brome grasses (Bromus spp.) before seed formation. The recommendation for these species is to graze the plants twice approximately three weeks apart at least two years in a row. Most people cannot put cattle, sheep, or goats in their yard, but poultry also graze. I have had excellent success in controlling downy and ripgut brome with chickens. They eat the shoots and scratch the roots from soil.
Herbicides can also be effective in controlling cool season annual grasses. Glyphosate will control annual grasses but is non-selective (kills all green plants it contacts). Pre-emergent herbicides are also effective, but must be applied prior to germination. Two selective grass herbicides (kill grasses but not broadleaf plants) are available and effective: sethoxydim and fluazifop-p-butyl. This is not a complete list of effective products, but is a starting point for those that want to use herbicides. Pesticide users should always read and understand the label before applying.
Regardless of the weed control method used, long-term success will only be achieved if the available growing space is occupied by desirable plant species. Weeds are simply a sign that unoccupied soil, excess water, and/or plant nutrients are available for them. Native or drought adapted perennial grasses and wildflowers can often be used to occupy available growing space and displace weeds in landscapes.
The University of Arizona Cooperative Extension has publications and information on gardening and pest control. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at firstname.lastname@example.org and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/.
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Last Updated: October 13, 2005
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