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United States Department of Agriculture

Agricultural Research Service

Title: Biological Control of Yellow Starthistle

item Smith, Lincoln
item Balciunas, Joseph
item Pitcairn, Michael - CDFA

Submitted to: Weed Science Society of California Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: January 8, 2001
Publication Date: December 1, 2001

Interpretive Summary: Yellow starthistle is an alien plant that probably originated from the eastern Mediterranean. It was first collected in California in 1869, and now infests 42% of the state's townships. It interferes with land use such as grazing and recreation, displaces native species, and is toxic to horses. This weed is much less invasive in its land of origin. This is presumably because natural enemies, such as insects, plant diseases, animals or competing plants help to keep it under natural control. We are exploring for insects and pathogens that attack this plant. They are tested for host specificity to make sure they do not attack other plants. After evaluation and approval by state and federal agencies, these agents will be released to try to reestablish the natural control that occurs in the land of origin.

Technical Abstract: Six species of insect biological control agents have been introduced to control yellow starthistle. All six attack the seedheads. The most promising agent is the hairy weevil (Eustenopus villosus), which is well established in California and occurs in high densities, attacking 25 to 80% of seedheads. However, this insect has only one generation per year and does not attack flowers that develop later in the summer. The false peacock fly (Chaetorellia succinea), which was accidentally introduced in 1991, emerges in the spring about a month before the plant has developed flower buds large enough for egg-laying. However, the fly has several generations per year and increases numbers progressively through the growing season, complementing the seasonal activity of the hairy weevil. The other established agents, Urophora sirunaseva, Bangasternus orientalis, Chaetorellia australis and Larinus curtus are fairly widespread but do not attain high numbers and appear to have little impact on yellow starthistle populations. The rust pathogen, Puccinia jaceae, has been evaluated for host specificity by William Bruckart at the USDA-ARS laboratory in Fort Detrick, MD. Foreign exploration and evaluation of additional agents is currently increasing in Turkey, Russia, Greece and Italy.

Last Modified: 4/21/2015
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