|Woods, Dale -|
Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: May 4, 2009
Publication Date: October 1, 2009
Citation: Woods, D.M., Smith, L. 2009. Preparation for the introduction of a new yellow starthistle biological control agent into California. In D.M.Woods, (ed.), Biological Control Program 2008 Annual Summary. California Department of Food and Agriculture, Plant Health and Pest Prevention Services, Sacramento, California.pp.43-46. Interpretive Summary: Yellow starthistle is an alien weed that has invaded about 20 million acres in the western U.S. It is especially abundant in Pacific western states. The spiny plant interferes with grazing livestock and outdoors recreation, it is fatally poisonous to horses, and it outcompetes desirable vegetation. Six species of insects and a rust fungus have been introduced as biological control agents, but they are not providing sufficient control. A weevil from Turkey, Ceratapion basicorne, attacks the roots of immature plants in the spring before the plant can reproduce. Host specificity evaluations have been completed and permission to release this weevil has been requested from USDA-APHIS. We have begun to collect baseline data on yellow starthistle populations at potential release sites in preparation of evaluating the weevil's efficacy.
Technical Abstract: Yellow starthistle populations were monitored at six locations in California. At each location, two sites were selected with the intention of using one as a future release site and one as a control site. Permanent transects were established and data were collected on plant density, plant size, number of seed heads per plant and per m^2, and attack rates of seed head insects. Yellow starthistle densities ranged from 41 to 507 and seed heads from 1.6 to 97.7 per m^2 at the various sites, indicating high variation between sites. The proportion of seed heads attacked ranged from 25 to 93%. The hairy weevil, Eustenopus villosus, was the most common insect, followed by the false peacock fly, Chaetorellia succinea. We will continue to collect data annually with the intention of measuring the impact of the rosette weevil, Ceratapion basicorne, after it is permitted for release.