1004077702 mothsrogue1.jpg

Weed-munching moths unleashed

SHADY COVE — An innocuous-looking moth with some bad-ass offspring may be on its way to becoming the weapon state agriculturalists employ against the newest invasive weed to spread like, well, weeds in Jackson County.

The Oregon Department of Agriculture has turned to the rush skeletonweed moth to help stem the spread of its namesake, a spindly and easily overlooked plant moving up the Rogue River banks and threatening to muck up agricultural pastures.

Both the moth and the weed hail from Eurasia, and the moth’s larvae is the only known caterpillar to feast on the plant’s deep roots.

Because the plants sport tiny leaves, they are not easily quelled by herbicides. So in introducing the little white moths, botanists hope their offspring will get to work to at least slow down the weed’s creep through the natural environment.

“They’re simple but elegant moths,” said botanist Kristi Mergenthaler, stewardship director for the Southern Oregon Land Conservancy. “Their (larvae) are bad-ass.”

The hope is that this form of “biocontrol” will slow the spread of the weed by decreasing root reserves and plant vigor, harming its abilities and stressing out the plants, but “eradication is probably impossible at this point,” Mergenthaler said.

Mergenthaler released 300 of the moths Friday in a relatively thick patch of rush skeletonweed on the conservancy’s Rogue River Preserve just north of Highway 234.

The hope is the moths will mate and deposit eggs on the skeletonweed and get their offspring munching away by fall, Mergenthaler said.

The moths were purchased from the Nez Pierce Tribe, which has a lab that produces biocontrol insects in Idaho, said Carri Pirosko, ODA’s integrated weed management coordinator for Southwest Oregon.

Friday’s release was the second in Jackson County, following a similar release last year along the Rogue near Gold Hill, Pirosko said.

Oregon has more than 60 insects approved as biocontrol agents for use against specific nonnative invasive species. The rush skeletonweed moth is a relatively new one, said Joel Price, biological control entomologist for the Oregon Department of Agriculture.

In its native Eurasia, the plant does well in drought conditions because of its deep roots, and its population is kept in check by natural predators, including the root-mining moth larvae.

Since its arrival here, rush skeletonweed has been able to spread unchecked in rangeland and cropland, particularly on low-elevation lands, according to ODA.

In cereal grain production, the weed’s latex sap can gum up grain harvesters.

With no North American pest available, biocontrols were introduced, Price said.

“If there were natives feeding on it, there would be no need for biocontrol,” Price said.

The moths have been released in three other Oregon counties, and there is no evidence they have eaten anything but rush skeletonweed, Price said.

It could be a slow go before rush skeletonweed moths become a fixture here.

ODA conducted experimental releases in Multnomah County as early as 2005, and a local population had taken hold by 2012, according to ODA.

In Douglas County, moths were released in 2008, and their progeny first surfaced in 2012 but were not seen the following year, according to the agency.

The plant travels along roadways and rivers, Mergenthaler said. On a recent Rogue weed-pulling float downstream of Shady Cove, Mergenthaler said she saw the spindly plant virtually everywhere she stopped.

“Because it’s so inconspicuous probably is why we feel like it’s just blown up in Jackson County,” she said.

Pirosko said it’s hard to guess how effective these rush skeletonweed moths will be against their namesake plant here.

“There’s such limited distribution, and the science isn’t there yet on how they’re going to respond in Oregon,” Pirosko said. “Biocontrol is not a silver bullet. It’s one more tool we have.”

Reach Mail Tribune reporter Mark Freeman at 541-776-4470 or mfreeman@rosebudmedia.com. Follow him on Twitter at www.twitter.com/MTwriterFreeman.

Share This Story