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Project description

Integrated management of medusahead and other noxious annual grasses and restoration of degraded grassland to desirable species. (01XN013)
Program Exotic Pests and Diseases Research Program
Principal
investigator
J.M. DiTomaso, Vegetable Crops, UC Davis
Host/habitat Rangeland; Grassland
Pest Medusahead Taeniatherum caput-medusae
Discipline Weed Science
Review
panel
Natural Systems
Start year (duration)  2001 (Three Years)
Objectives Develop an effective integrated strategy for controlling medusahead and other undesirable annual grasses and re-vegetate degraded exotic annual dominated grasslands to an ecosystem with high forage quality or native plant diversity, and resistance to subsequent re-invasion by undesirable species.

Test the effect of imazapic (Plateau®) at several rates on the control of various annual grasses in a rangeland ecosystem. Determine whether >30% residue cover (heavy thatch) reduces the control of annual grasses.

Determine the tolerance of several species of wheatgrass to imazapic and utilize the most insensitive species in the subsequently restoration study.

Evaluate an integrated approach using prescribed burning, imazapic, and combinations of the two methods for control of medusahead and other annual introduced grasses.

Utilize imazapic and prescribed burning to establish desirable forage or shallow and deep-rooted native species capable of preventing re-invasion by undesirable invasive species.

Final report Effect of medusahead thatch on imazapic control: Removal of thatch dramatically improved imazapic efficacy, whether the removal technique was burning, tillage, or mowing. This suggests that imazapic ties up in the thatch layer. Furthermore, removing thatch reduced medusahead in the following year even without using imazapic. This supports previous reports that thatch enhances the competitive ability of medusahead in annual grasslands.

Tolerance of perennial grasses to imazapic: In rate series trials, high rates (140 g ae/ha) of imazapic gave nearly complete control of medusahead, bulbous bluegrass, and downy brome, but left vigorous stands of intermediate and pubescent wheatgrass and native squirreltail.

Integrated management and restoration with native species: We established four integrated management sites, two in the Central Valley (Fresno and Yolo counties), and two in northern cool-winter locations (Siskiyou and Lassen counties). In the Central Valley, prescribed burning was a very effective treatment, providing 90% to 100% control of medusahead after a single burn. Two years of burning, one year of burning plus one year of a high rate of imazapic, or two years of high-rate imazapic produced 95% to 100% control of medusahead. But including a burn in the final year of treatment resulted in higher populations of broadleaf forage plants. Imazapic used alone greatly reduced forate quantity and increased populations of undesirable composites such as catsear (Hypochaeris spp.) and tarweeds (Hemizonia spp.). In Siskiyou County, only the two-year burn treatment, or two high-rate applications of imazapic, produced control of 95% or better. Again, forage composition was better following burning. In Lassen County, only a spring treatment with imazapic produced good control while resulting in 97% bare ground. Early medusahead studies suggested that control with burning in cold-winter areas was poor. Our trial in Lassen County supports this claim, and our forage analysis suggests the cause may be insufficient dry forage (fuel) to kill medusahead seeds by heating.

Reseeded species did not establish at either Fresno or Yolo counties owing to fall or winter drought. Seeded wheatgrasses established at Siskiyou County and are continuing to expand.

Third-year
progress
From our original proposal we delayed the Siskiyou County treatment site for another year because of a lack of rainfall. This resulted in very little vegetation on the experimental site, including almost no medusahead. As a result, we added a third site in Yolo County. Our initial vegetative analysis was conducted in April 2002, in both sites and all treatments were made during that year. We also set up similar plots in Lassen County. Due to the high number of fires in Oregon in 2002, the Bureau of Land Management could not conduct the prescribed burns at this area, but the burn was conducted in the summer of 2003. We now have five sites (Yuba, Yolo, Siskiyou, Lassen, and Fresno counties) we are evaluating, with only two receiving all treatments. The other three sites will receive their final treatments in 2004. Our results for the two sites receiving all treatments indicates that imazapic is effective on medusahead control, but only in areas lacking a significant thatch layer (Fresno County was grazing in winter to remove thatch). In Yolo County, where the thatch layer was considerably thicker (no winter grazing), imazapic treatments were ineffective, even at the highest rate. By comparison, prescribed burning was a very effective treatment, providing 99% and 87% control of medusahead after a single burn in Fresno and Yolo counties, respectively. The combination of a summer burn (which removed the thatch), followed by a fall imazapic treatment at the high rate, provided 100% control in both locations. Experiments in Lassen, Yuba and Yolo counties also indicated that removing the thatch by either tillage, burning, or mowing reduced the competitiveness of medusahead and gave an average of 50% reduction in medusahead even before the herbicide treatment. Finally, the reseeded native perennial grasses and broadleaves did not establish at either the Fresno or Yolo County sites. We hypothesize that this was due to the four- to six-week rain-free period in December 2002, that likely caused the germinated seedlings to desiccate before establishing.

Second-year
progress
This is the second year of the proposal. From our original proposal we had to delay the Siskiyou County treatment site for another year because of the lack of rainfall. This resulted in very little vegetation on the experimental site, including almost no medusahead. As a result, we added a third site in Yolo County. Our initial vegetative analysis was conducted in April 2002 in both sites and all treatments were made during that year. Preliminary analysis indicated that medusahead represented 29 and 27%, respectively, of the vegetative cover in the Yolo and Fresno County plots. We also set up similar plots in Yuba and Lassen counties. However, an accidental wildfire caused by a electrical problem destroyed the Yuba County site. A new site has been chosen and the baseline evaluations will be made in late April, 2003. The Lassen County site was also initially evaluated and was ideal for the proposed study. However, due to the high number of fires in Oregon in 2002, the Bureau of Land Management could not conduct the prescribed burns at this area. We are currently setting up new plots in Lassen County and attempting to repeat the study again. Thus far we have spent a considerable amount of time and energy in an attempt to expand this project to five areas in California representing very different ecosystems infested with medusahead. Unfortunately, we only have two sites that are currently in progress, with the hope that the remaining three will be treated this year. Of the two in progress, all treatments were made with no problems, and the first year post-treatment evaluations will be conducted in late April to July of 2003. Our preliminary results will be presented at the October workshop.

First-year
progress
This is the first year of the proposal. The sites for the study have been identified and the plots staked and fences built. In mid- to late April we conducted our initial evaluation of the percent species cover in all plots within the Yolo and Fresno County sites. Preliminary analysis indicates that medusahead represents 29 and 27%, respectively, of the vegetative cover in the Yolo and Fresno County plots. We are currently drying the collected plant material for forage quality and quantity analysis. In early May to June we will evaluate the Yuba, Siskiyou, and Lassen County sites (peak flowering) and will conduct the respective treatments during late spring, summer, and fall 2002. Our preliminary results will be presented at the October workshop.

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