Tiny rodents are damaging grass seed crops worth tens of millions of dollars. The gray-tailed rodents, Voles have been chewing away crops, especially the annual ryegrass, a staple of Oregon’s grass seed crop, are now moving into vineyards and orchards. They are also known as field mice or meadow mice. A perennial problem for Oregon farmers, their population is exploding every few years. To worsen things, an unseasonably wet spring damaged the grass seed crop gravely in one of the world’s leading producer states. This year, the Voles devoured up some 60 million to 80 million pounds of grass seed. This adds up to about 10 percent of a crop that yielded 783 million pounds last year, or about $35 million in losses, according to the executive director of the Oregon Seed Council.