At Pinnacles National Park, out of approximately 625 plant species, about 100 are nonnative. Those nonnative plant species with the potential for creating serious ecological damage by displacing the park’s native plant community are called "invasive." Pinnacles National Park Weed Control Program is focused primarily on yellow star thistle (Centaurea solstitialis), Italian thistle (Carduus pycnocephalus), horehound (Marrubium vulgare), and mustard (Hirschfeldia incana). Weed control efforts focus on these four species because of their potential for native habitat destruction. Yellow star thistle and mustard are controlled by working through a sequence of large areas on a monthly basis. Horehound is much closer to being eradicated within the park and is controlled by monthly visits to 140 small plots. Eradication methods include hand pulling and herbicide application.
Yellow star thistle
Yellow star thistle, or “the plant that ate California,” has already degraded over 25% of the state's land and is considered one of the most invasive weeds by the California Exotic Pest Plant Council. Yellow star thistle is a summer-blooming annual in the sunflower family and native to Eurasia. The plant is often initially found in open, disturbed areas such as former ranch lands, road edges and stream channels. Through time it moves increasingly into undisturbed locations, including meadows and riparian corridors.
Last updated: March 19, 2019