TERRETON, Idaho — Many farm fields were so cratered with vole holes last fall, agricultural pilot Leif Isaacson said they resembled a moonscape from the air.

In the midst of one of the mildest winters in memory, Isaacson, owner of the Desert Air Ag crop dusting service, fears already abundant vole populations are only proliferating. He said the stubby-tailed rodents could pose major headaches this season for alfalfa growers in pockets throughout Eastern Idaho, including Mud Lake and Terreton.

“A lot of times these mice populations die off over the winter,” Isaacson said. “This winter, there’s no shortage of them. They’re able to dig anywhere they want right now.”

Isaacson’s hangar has an omnipresent, garlic odor — added to zinc phosphide vole pellets as an attractant.

The pellets must be applied in dry weather, or else they gasify and waste the active ingredient. He applied the pellets on thousands of acres last fall, and he’s heard from several growers this winter who lament that they didn’t have him treat more land.

He believes voles found both food and cover in hay windrows that growers left in fields last fall while waiting for a break in wet weather.

Idaho Falls farmer Matt Gellings had vole bait aerially applied in alfalfa during late December, at a cost of about $20 per acre.

“There’s definitely some vole damage out there,” Gellings said. “Last spring, I didn’t think I had that much of a problem, but last fall, they were terrible. Talking with other hay guys around me, they’re just terrible right now.”

University of Idaho Extension forage specialist Glenn Shewmaker has seen more vole activity than normal this winter in the Kimberly area.

“I thought maybe we had hit a down cycle, but they appear to be doing well,” Shewmaker said.

The USDA Animal and Plant Health Inspection Service’s Supply Depot in Pocatello manufactures agricultural zinc phosphide to order and has noticed heightened demand since November, said facility manager Patrick Darrow.

Darrow said the demand was initially from alfalfa growers in Utah’s Cache Valley, but he’s fielded several orders in Idaho since the start of the new year, especially from the American Falls, Aberdeen and Bancroft areas.

During the first two months of 2014, Darrow said growers bought 800 pounds of zinc phosphide. Already in 2015, he’s sold about 5,000 pounds.

Will Ricks, president of the Idaho Hay and Forage Association, said voles have been known to damage up to 35 percent of an alfalfa crop. Though they haven’t been especially bad in his growing area in Monteview, he’s heard reports of high densities north of Idaho Falls.

Reports from UI Extension educators have been mixed.

Fremont County Extension educator Lance Ellis has fielded an average number of vole calls. John Hogge, Extension educator for Clark and Jefferson counties, said voles have been “absolutely terrible this year.”

Reed Findlay, Extension educator for Bingham and Bannock counties, said he’s had more vole calls from growers than normal, but he also suspects growers may be more aware of their vole problems because rodent holes are now exposed due to a lack of snow cover.

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