VOLES GORGE ON VALLEY CROPS WITH VENGEANCE.

Byline: Tim Christie The Register-Guard

Hordes of tiny rodents have chewed up prodigious volumes of Oregon's valuable grass seed crop this year, causing tens of millions of dollars in losses. Now they're moving into vineyards and orchards.

Gray-tailed voles are a perennial problem for Oregon farmers, but every few years their population explodes, and these pesky rodents, also known as field mice or meadow mice, turn from nuisance pests to voracious destroyers.

The vole invasion, combined with an unseasonably wet spring that caused major damage to the grass seed crop, have made 2005 a year growers won't soon forget.

"It seems like a double whammy this year," said Shedd farmer George Pugh. "This is the worst I've seen."

Voles gobbled up some 60 million to 80 million pounds of grass seed this year, about 10 percent of a crop that yielded 783 million pounds last year, said David Nelson, executive director of the Oregon Seed Council. That's roughly $35 million in losses, he said. Oregon is the world's leading producer of grass seed.

"It's going to be a huge financial hit on a lot of those guys," he said.

Annual ryegrass, a staple of Oregon's grass seed crop, was hit especially hard, suffering a 40 percent crop loss, based on preliminary estimates, said Mark Mellbye, field crops agent for OSU Extension in Linn, Lane and Benton counties.

"This is the worst (outbreak) on record for the south Willamette Valley and caused the worst damage to our seed crops that anyone can remember," he said.

The U.S. Department of Agriculture last month declared nine Oregon counties agriculture disaster areas because of weather and vole damage, which made farmers who suffered crop losses of 30 percent or more eligible for low-interest emergency loans if they were no longer able to get bank financing.

So far about 75 grass seed farmers have sent notice of crop losses to the USDA's Farm Service Agency, though not all will apply or be eligible for loans, said farm loan manager Patrick Joerger.

Farmers are doing what they can to fight voles, said Nelson of the Seed Council. The one pesticide legal to use against voles is zinc phosphide, but it can be spread widely only from May 1 to Sept. 1, he said. After Sept. 1, farmers can use it on a spot basis by putting treated oats or pellets down mouse holes - an extraordinarily labor intensive project.

Farmers are now keeping their collective fingers crossed for a cold, hard winter and an outbreak of tularemia, a rodent disease that would crash the vole population back to regular, manageable numbers.

Pugh, who grows grass seed, wheat, orchard grass and meadowfoam on 2,700 acres, said he's doing more plowing than he would normally do to disrupt the voles' habitat.

He also plans to put pesticide in their burrows, but the labor costs make it hard to do extensively.

Pugh said voles destroyed as much as 50 percent of the crop in some fields, while other fields suffered less damage. The fields that weren't tilled were hit hardest because they had more cover for voles, while those where sheep grazed, reducing the cover for voles, fared better, he said.

Voles also hurt the quality of the seed that did survive, he said. They left mounds of dirt that farm equipment kicked up into the seed. That made it hard to clean the crop and get it ready for market, he said.

No one knows for sure what caused vole numbers to increase exponentially this year, but there are several working theories, all involving aberrant weather and the fact that voles are prolific breeders.

Early rain in fall 2004 caused grasses to grow quickly, providing food and shelter for the voles. Then a mild, sunny and dry winter allowed vole population numbers to grow instead of crash, Mellbye said.

That mild weather allowed voles to make babies at an astonishing pace. Females can get pregnant starting 28 days after birth, when food is abundant, and their gestation period is 21 days, with litters of four to six, according to Oregon State University research.

This fall, as green vegetation has gone away, voles have begun adding variety to their diets by moving into vineyards and orchards up and down the Willamette Valley, said Ross Pennhallegon, horticulture agent for OSU Extension in Lane County.

Pennhallegon said he's taken calls from two vineyards where 10 percent of their vines had been girdled - meaning pests had chewed of the bark around the base of the vine. Voles also will go after bulbs, shrubs, berry vines and tree fruits, he said.

"There's a real potential for disaster that people need to be aware of," he said. "They need to just ratchet up their awareness levels."

None of the Southern Willamette wineries contacted for this story reported any vole-related problems in their vineyards.

While the vole explosion has been bad news for growers, it's meant good eats for animals higher up the food chain. Raptors, coyotes, skunks, foxes, snakes, raccoons, herons and cats all feast on the rodents.

"They're the Gummi Bears of the animal world," said Dan Edge, head of the Department of Fisheries and Wildlife at OSU. "They're a nice little packet of protein."