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Progress in Yellow Starthistle Biological Control

By Kathryn Barry Stelljes
February 22, 1999

A depressed patch of weeds in the Idaho wilderness is good news for land managers. That’s because the depression provides some of the first visible success by an imported six-legged natural enemy of yellow starthistle.

Known to scientists as Centaurea solsitialis, yellow starthistle is among the top 10 worst weeds in several western states and covers tens of millions of acres. It can kill horses that eat it, and other livestock will eat only small portions of very young plants. The weed displaces other plants as it spreads, and turns prime grazing land into worthless weed pastures.

But a small beetle named Eustenopus villosus is beginning to tame yellow starthistle. Female beetles lay eggs in older buds and the larvae eat most of the maturing seeds before they can disperse.

The beetle is the latest of five natural enemies imported by the Agricultural Research Service from the weed’s homeland in Eurasia. The insects were released after years of safety and efficacy testing by several ARS scientists. Cooperators, such as University of Idaho researchers, monitor and redistribute insects from the initial release sites.

Biological control is viewed as the best long-term strategy for managing the weed. Once it takes over, physical controls like cutting or pulling it can’t keep up. Chemical control is too expensive for widespread use on rangeland and may be environmentally undesirable.

Joe Balciunas, an entomologist at the Exotic and Invasive Weeds Research Unit in Albany, Calif., leads ARS’ ongoing research effort to apply biological control to yellow starthistle. He’s comparing the weed's seed production in the U.S. and in one of its native countries, Turkey, where yellow starthistle doesn’t run amok. The goal is to reproduce here the conditions that keep the weed in check there.

A story about yellow starthistle research appears in the February issue of the agency’sAgricultural Research magazine and on the web at:


The Agricultural Research Service is the chief scientific agency of the U.S. Department of Agriculture.

Scientific contact: Joseph K. Balciunas, ARS Exotic and Invasive Weeds Unit, Albany, Calif., phone (510) 559-5975, fax (510) 559-5963,