Yellow starthistle has overtaken pasturelands in the Battle Creek watershed and elsewhere throughout California but it can be eradicated through proper management techniques.
This plant is toxic to horses in large amounts, causing equine nigropallidal encephalomacia ("chewing disease"). The first signs of poisoning are an inability to eat or drink as the muscles of the lips, face, and tongue become stiff and swollen, giving the horse a fixed expression. Poisoning eventually results in permanent brain damage, and severely affected animals eventually die of thirst and starvation (Kingsbury 1964; Cordy 1978).
Once it has colonized an area, yellow starthistle can quickly spread and displace other vegetation. Even after control measures have been implemented, yellow star-thistle can quickly re-establish if competitive replacement species are not established. Conventional methods (usually chemical) for yellow starthistle control have often failed on because of lack of competitive vegetation, developed seed banks, high cost of control, size of infestations, and lack of long-term commitment (Coombs et al. 1996). |
Eustenopus villosus is a species of weevil known as the yellow starthistle hairy weevil.
The female weevil chews a hole in the closed flower head of yellow starthistle, deposits an egg inside, and seals the hole with a dark-colored mucilage. This visible hole can warp the shape of the flower head as it grows. The larva emerges from its egg in about three days and begins to feed on the flower parts and developing seeds. In just over two weeks the larva can destroy all or nearly all of the developing seeds. It uses the scraps to build a chamber in which it pupates for one to two weeks and then leaves the flower head as an adult. Both larva and adult of this species contribute to the damage done to the plant. The larvae eat the seeds in mature flower buds and the adults feed on smaller buds, destroying many. This weevil will readily attack many invasive Centaurea species, but has not been known to damage native flora.This weevil is native to southern Europe and the Mediterranean. It was first released as a biocontrol agent in the United States in 1990 and it is now established in much of the western United States wherever yellow starthistle grows. It is considered one of the more efficient yellow starthistle biocontrol agents. |
Yellow Starthistle Management on Small Acreages
Yellow Starthistle - Integrated pest management for home gardeners and landscape professionals.
Yellow Starthistle Management Guide - Published by the California Invasive Plant Council, provides comprehensive information about the plant's introduction and spread, its biology and ecology, methods of biological, mechanical, cultural and chemical control, and how to develop a strategic management plan.
Yellow Starthistle Biology and Management in Pasture and Rangeland - A guide produced by the University of Idaho Cooperative Extension System's College of Agriculture.
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