Successful Burning Strategy to Control Barbed Goatgrass
Barbed goatgrass (Aegilops triuncialis) is an introduced annual grass that is spreading throughout California grasslands. It is listed as a noxious weed by the California Department of Food and Agriculture and as a wildland weed by the California Exotic Pest Plant Council. When mature, it is unpalatable for livestock. In grasslands, Barbed goatgrass reduces the abundance of native perennial bunchgrasses and competes with more desirable introduced annuals, as well as native forbs. Unlike many other introduced annual grasses found in California, this species appears to do well on serpentine soils that are generally resistant to the spread of annual grasses and therefore are thought of as refugia for native plants.
In California, the removal of periodic fire has dramatically changed the composition of rangelands. For noxious annual grasses such as barbed goatgrass, medusahead, and ripgut brome, fire suppression can lead to their dominance in grasslands. These noxious annual grasses all rely on animal dispersal for their spread. To facilitate this, they do not shed their seeds until much later in the season compared to more palatable annual grasses such as ryegrass, wild oat, and soft chess. This provides a window of opportunity for using timely pres-cribed burning as a method to destroy existing goatgrass plants and prevent new seed production while causing mini-mal damage to desirable grass seed on the soil surface. In addition, repeated properly timed burns can remove litter and recycle nutrients. Fire has also been shown to control other invasive species, including yellow starthistle, and to stimulate tillering and increase perennial bunchgrass populations.
FIGURE 1: Average percent cover of goat grass from 10 burn and 10 no burn transects in two pastures.
In mid-May of 1997 and July 1998, we burned two pastures with extensive amounts of barbed goatgrass at the Hopland Research and Extension Center. The burns were conducted at a time when the spikelets were still contained in the inflorescence but before any seed matured to viability. At this stage the undeveloped seed coats are more vulnerable to fire. This occurs at different times each year due to differences in rainfall patterns. In each of these areas, measurement of barbed goatgrass control and changes in vegetation composition were compared with an adjacent unburned control site. Our findings indicate that at some sites a single complete burn reduced barbed goatgrass by an average of 84%. After two consecutive years of complete burn, barbed goatgrass appeared to be eliminated in one pasture. In this site, no seedlings or mature plants were detected. In the second pasture we burned an upper section with more serpentine soil and a lower section. Both areas burned completely in the first year. However, in the second year approximately 8% of the upper section and 56% of the lower section did not burn. This was primarily due to a lack of combustible fuel. After two years, we achieved 98% goatgrass control in the upper region and only 75% control of the noxious weed in the lower site. When all the sites are averaged together, excluding the site that did not burn completely, a 92% reduction in goatgrass abundance was achieved following two burn seasons (Figure 1).
Prescribed burning also impacted the vegetative cover and frequency of many species in the burned and unburned sites of both pastures. In general, the presence of introduced species other than barbed goatgrass (e.g., soft chess and hedgehog dogtail) was reduced following burning. By comparison, several native species increased, including native perennial grasses, most notably meadow barley (Hordeum brachyantherum), and several native forbs, particularly legumes.
In summary, prescribed burning, timed before the production of viable seed, can be a very effective tool for barbed goatgrass control. However, unless two consecutive years of controlled burn can be achieved, this weed will not be eliminated.
Above: Hopland Research and Extension Center staff burning to control goatgrass.
prepared and edited by Adina Merenlender and Emily Heaton