Return of the vole — Willamette Valley faces resurgence of crop-destroying rodents | Enterprise

A massive increase in the population of gray-tailed voles devastated the farmland in the Willamette Valley for the second year in a row.

According to researchers, vole populations peak in cycles. The last big population boom in the valley was about a decade ago. The number of gray-tailed voles rose again in 2020, and pressures will rise by 2021.

“(2020) was the most extreme year we’ve seen in recent history,” said Nicole Anderson, associate professor and agronomist in crop expansion at Oregon State University.

Anderson expects more serious crop damage in 2021.

Voles feed on roots, grasses and other living plant material. They dig underground and sometimes pull blades of grass into their holes.

Voles damaged grass seeds, hazelnuts, blueberries, clover and nursery crops last year.

Bryan Ostlund, who represents blueberries, clover, grass seeds and other commissions, said the grass seed industry has been hardest hit.

Industry leaders estimate that voles destroyed 10% to 30% of the 2020 crop. That’s a “very conservative” estimate of $ 50 million in loss, said Roger Beyer, executive director of the Oregon Seed Council.

Many fields suffered a loss of 75% to 80%.

“It was heartbreaking,” said Steve Salisbury, director of research and regulatory programs for the Oregon Seed Council.

One grass seed producer, Becky Berger of Berger International, lost about $ 400,000 in income. In some fields that were predicted to produce 3,000 pounds, the yield was only 700 pounds.

Berger described the events as “extremely frustrating” and “economically scary”.

This spring, she said, she had seen an increase in vole activity lately.

Voles also target other crops, including red and white perennial shamrocks, blueberry bushes, and hazelnut trees. Even ranchers have noticed pasture infestation.

“It takes a lot of patience to deal with this mess,” said Donna Harnsberger, who raises cattle, horses and llamas on a small ranch in Cottage Grove.

Researchers say gray-tailed voles are under-discussed, so it’s not clear why populations tend to fluctuate and then collapse. Some theorize that severe winters and pathogens can cause populations to crash.

There is little that breeders can do to control voles. For years, zinc phosphide, or ZP, a rodenticide, has been the only state registered product for killing voles.

But the poison has limits. When used above ground, ZP can kill wildlife. From September 15th to May 1st of each year, breeders cannot use ZP above ground as this could harm wild geese.

Growers are waiting this spring for the state ministry of agriculture and the state ministry of fish and wildlife to signal that geese have left for the season.

Until then, farmers are only allowed to use ZP underground – a time-consuming method with questionable effectiveness.

Despite the frustrations, growers say they hope for new research starting this year.

After last year’s devastation, the Oregon Seed Council and various commissions pooled $ 80,000 to fund a research project.

The council is funding wildlife biologist Jimmy Taylor of the National Wildlife Research Center to conduct a vole study this spring and summer. Taylor’s team will test which factors make ZP more or less effective and how baits become more attractive.

“I look forward to getting this research off the ground,” said Taylor.