Proceedings of the Vertebrate Pest Conference

The physical impact of voles in agriculture and forestry has been duly noted by many researchers around the world. The economic impact of the various species, however, has not received much attention other than to note that losses from these animals can be substantial when population levels become high. This study assesses the economic impact of an extremely high population of Microtus montanus (mountain voles) in a large apple (Malus sp.) orchard in northcentral Washington State (U.S.A.) over a two-year period. In this study, 200 trees were harvested, weighed, graded, and compared by the amount of visual damage that could be seen above the soil surface. These values were then compared with cash values received by growers for the season. Production was decreased a weighted average of 36% (31% for red delicious and 53% for golden delicious) or $3036/ac. ($7500/ha.) during the first year. In the second year, production increased 3.2 fold but still did not reach that of the control orchard. If 30% of the orchards in the state were to suffer the same level of infestation, over $137 million/year could be lost because of poor management and control programs.