Southern Oregon land trust turns to insects to control invasive species

Canada thistle is an invasive species that conservation specialists hope to bring under control in Southern Oregon by using two species of insects. (Thomas Nugent/geograph.org.uk/Wikimedia Commons)

Canada thistle is an invasive species that conservation specialists hope to bring under control in Southern Oregon by using two species of insects. (Thomas Nugent/geograph.org.uk/Wikimedia Commons)

By The Associated Press on May 09, 2014 at 5:22 PM, updated May 09, 2014 at 5:24 PM

SPRAGUE RIVER — “Here’s one!” shouted Steve Sheehy, pointing to the ground near a barbed wire fence in the Sprague River Valley.

“The questions is, ‘How many flies have emerged?’ ” Victoria Tenbrink called back.

Tenbrink, the Klamath Lake Land Trust conservation manager, and Sheehy, a lichenologist, are searching for the cache of woody gall fly pods they dropped at the 316-acre KLLT property in March.

The bulbous pods, which develop after a female gall fly lays eggs on a thistle stem, contain matured flies that will prey on Canada thistle. About 100 gall pods were scattered at the property earlier this spring. Now, Tenbrink is adding stem-mining weevils as another method to biologically control invasive Canada thistle.

“We prefer a combination of those two control agents together,” said Eric Coombs, an entomologist for the Oregon Department of Agriculture.

Before releasing the 50 minuscule stem-mining weevils Tenbrink ordered from the ODA, she cautiously peeked inside their cylindrical shipping container.

“They look like they are in really good condition. We have high hopes,” Tenbrink said. “If they take, they’ll move out and help the whole Sprague valley.”

In January, the Klamath County commissioners approved the noxious weed list for 2014, which classifies Canada thistle as a “B list” noxious weed in Klamath County. Fifteen plants are on the B list, indicating a species is abundant in the county, but may have limited distribution.

According to Todd Pfeiffer, Klamath County vegetation manager, Canada thistle has been established in the county for years.

“It’s extremely widespread. It’s not ever going away,” he said.

Tenbrink said Canada thistle is most abundant in disturbed areas along the fence line and ditches of Land Trust’s property, which is being converted to nonirrigated pasture. Tenbrink doesn’t expect the weevils and gall flies to eliminate the thistles, but she said she believes the insects will help make the infestation more manageable.

“They are never going to wipe out the plants,” Tenbrink said of the weevils, “but they can weaken the population to be more susceptible to other control methods.” Continue reading….