OREGON STATE UNIVERSITY

New weevil takes a bite out of puncturevine

09/27/2002

PENDLETON - An insect is helping Oregonians in the Columbia Basin combat puncturevine, a plant that stabs livestock, rips wool, ruptures bicycle tires and pokes through tennis shoes.

The weed has been a thorn in the side ever since it hitchhiked to North America from southern Europe more than a century ago. Despised by bicyclists, gardeners and ranchers alike, the annual vine spreads across dry pastures and roadsides, armed with hard, spiny burs that break apart into several pieces that look, and act, like tacks.

A newly established weevil has joined the fight against the pesky weed. Mary Corp, a crop specialist for OSU Extension Service in Umatilla County, confirms that a population of puncturevine seed head weevil, Microlarinus lareynii, is chomping its way through the weed in Oregon's Columbia Basin.

The female weevil chews into the developing bur and deposits her eggs into the seed. Weevil grubs grow inside the seed, feeding on its contents before emerging as adults. Up to three generations of weevils can be produced in a year before overwintering as adults, according to Corp.

Introduction of seedhead weevils has controlled puncturevine in milder parts of the country, but until now, the bug has not taken to our colder winters.

"The current population is from a release made in 1996 by a homeowner in Umatilla," Corp said. "We have not had a severe winter in a number of years and this probably is contributing to their success."