Yellow starthistle is an aggressive annual forb that has invaded millions of hectares of California's annual range. Control efforts such as burning and herbicides have been effective for short-term management. However, recruitment from the seedbank or reinvasion of the annual grassland system results in a rapid return to yellow starthistle dominance. Establishing perennial grasses would be ideal for suppression of yellow starthistle. However, a lack of effective weed control options in California during a seeding program has limited perennial grass establishment. Clopyralid was used to control yellow starthistle annually for 1, 2, or 3 yr to provide a window of reduced competition for pubescent wheatgrass establishment. Total plant cover, yellow starthistle density, biomass, and seedhead number were quantified for 6 yr. Clopyralid treatment significantly reduced yellow starthistle and allowed pubescent wheatgrass establishment with a single treatment. Both clopyralid treatment and pubescent wheatgrass establishment significantly affected the range plant community composition. Annual grasses and forbs increased in plots only treated with clopyralid for 2 or 3 yr, whereas clopyralid-treated pubescent wheatgrass plots maintained lower annual grass and forb cover. Integrating pubescent wheatgrass seeding with clopyralid treatment provided long-term yellow starthistle suppression, whereas clopyralid treatment alone resulted in a plant community susceptible to repeated invasion. These findings support the establishment of competitive perennial grasses in annual grasslands as an important component of long-term yellow starthistle management.
Nomenclature: Clopyralid; yellow starthistle, Centaurea solstitialis (L.) #3 CENSO; pubescent wheatgrass, Thinopyrum intermedium (Host. Barkworth and Dewey) Nevski var. ‘Luna’.
Additional index words: Integrated management, revegetation.
Abbreviation: MANOVA, multivariate analysis of variance.