Date of this Version
Damage to fruit trees, tree seedlings and a wide array of ornamental shrubs by microtine rodents remains a widespread problem in both Europe and North America. Careful studies that quantify the levels of damage caused by a known density of rodent pests are not available. For this reason the orchard manager. Pest Control Specialist, and the researcher have a difficult time making wise decisions that are based on solid economic data.
There are several reasons for this lack of knowledge. The damage done to apple trees is not easily observed, described, or measured. There is probably not a simple linear relationship between bark removal and economic damage. In addition to these difficulties and because the tree is a perennial, there is cumulative damage as well as recuperative and compensatory processes. In numerous situations, compensatory growth has been suggested and actually demonstrated (Dyer 1973, 1975, 1976, Dyer and Bokhari 1976, Harris 1974, Hutchinson 1971, Pearson 1965, Vickery 1972, Westlake 1963, and Woronecki et al. 1976).
To date, only a few attempts have been made to address the economics of pine vole or meadow vole damage in orchards. Pearson (1976, 1977) and Pearson and Forshey (1978) examined the relationship between the presence of voles and tree damage expressed as a reduction in crop value. A few authors have made some theoretical and speculative estimates of damage (Kennicott 1957, Hamilton 1938, Garlough and Spencer 1944, Biser 1967, and Byers 1974). Recently Sullivan et al. (1980) have reported some standard survey work examining the magnitude and causes of tree mortality. This gives some concept of economic damage, but cannot be used to isolate even the benefits of current rodent control techniques. Ferguson (1980) and Luttner (1978) have also produced some very broad economic generalizations by extrapolating from rodenticide use figures. These, however, are only measures of standard acceptable orchard practice, and cannot form the basis for vole management in orchards.