Federal Government Approves Release Of Non-Native Weevil In California To Combat Invasive Thistle

(AP) — Federal officials have approved turning loose a non-native insect to feed on an invasive thistle that sprouts in everything from rangelands to vineyards to wilderness areas, mainly in the U.S. West.

The U.S. Department of Agriculture said Tuesday it will permit use of the weevil native to Europe and western Asia to control yellow starthistle, which is from the same areas.

Brad Hanson, UC Cooperative Extension weed specialist at UC Davis, says yellow starthistle thrives in part because of its prickly spines.

"So it's not very palatable to any livestock, especially once it's started to flower, and it's toxic to horses. So often times the other grasses and more palatable plants are grazed and the starthistle persists and is sort of the only thing left,” he said.

The spines also help the weed spread as it hooks on to vehicles, farm and lumber equipment, animals and clothes. Hanson says yellow starthistle can be managed on a small scale with chemicals, but that method just doesn’t work with the scale of infestation in the state.

“It's difficult to control economically on the millions and millions of acres of rangelands or non agricultural lands that are sort of minimally managed,” he said.

The U.S. Agriculture Department said yellow starthistle entered California before 1860 and is now one of the state's worst pests. Idaho, Oregon and Washington also have heavy infestations of the thistle that's been found in 41 states.

The USDA says its been  testing the weevils at a lab in Albany, California, to make sure they won't attack native plants or cause some other environmental damage. 

The weevils will initially be let loose in California, with additional releases in Idaho, Oregon, Washington and possibly Nevada. The agency said Wednesday it is accepting permit applications to process this fall so weevils could be released in the spring.

"We're really excited about the release of this weevil," said Jeremey Varley of the Idaho State Department of Agriculture. 

Before Idaho could release weevils, he said, the state will have to grow enough of them to have a large enough population to put into the wild. How long that might take isn't clear. The University of Idaho, which has an agricultural college, would likely play a role in that effort.

Experts say the weevil can reduce the spread of yellow starthistle where other methods, such as pesticides and physical removal of the plant, have failed. Yellow starthistle is an annual with a taproot. It spreads with seeds blown by the wind.

The insect's larvae feed on the upper part of the plant's root for about two months before going into the pupa stage inside the plant. They emerge as adults in June and feed on the yellow starthistle leaves for several days before, experts believe, becoming dormant.

The following spring, females feed for several weeks, then lay a few eggs on starthistle plants each day for several months before dying.

The federal agency has released an environmental assessment and finding of no significant impact to releasing the weevils. In 2009, it released a draft environmental assessment and spent the next decade testing to make sure releasing the weevils wouldn't have unintended consequences.

CapRadio's Drew Sandsor contributed to this report.