Vole damage to cover-cropped soybeans: exploring options of biological and cultural control
Cover cropping, the practice of planting a non-commodity crop between rotations of commodity crops, is an emerging conservation practice in row-crop agriculture. Cover crops are used to improve soil health and reduce the need for chemical inputs. Cover crops also provide habitat for wildlife in fields that typically are not utilized by most wild occupants of highly fragmented agroecosystems. Though increasing wildlife habitat generally is viewed as a benefit, presence of some species may conflict with economic goals of producers. Voles (Microtus), a genus of rodent typically found in grassland habitats, have been reported by producers to consume the commodity soybean (Glycine max) crop, however, few evidence-based strategies exist to prevent vole use of fields and subsequent damage. I examined how voles perceive cover crops as a source of habitat and how fields may be monitored and manipulated to prevent damage by voles.
I conducted captive feeding trials to identify common cover crops selected as forage by 10 meadow (M. pennsylvanicus) and 15 prairie voles (M. ochrogaster). I also gathered data on landscape features, weather conditions, and farming techniques for 66 cover-cropped fields and identified factors most important to predicting vole damage to soybeans. Lastly, I surveyed 38 cover-cropped fields for vole sign and explored other covariates, including cover-crop density, that contributed to vole damage to young soybean plants.
Both meadow and prairie voles commonly preferred clover (Trifolium), alfalfa (Medicago sativa), and hairy vetch (Vicia villosa) cover crops as forage, whereas canola (Brassica napus) was avoided by both vole species. Cover crops that were highly (or minimally) preferred were selected (avoided) more consistently than plants that were moderately preferred. Selection of cover crops by voles was affected by diversity of available forage, nutritional characteristics of the plants, and individual vole personalities.
Probability of vole damage to cover-cropped fields was most strongly tied to soil type, days of snow, and permanent grassland habitat available. Fields that had been cover cropped for >3 years, had not been tilled, contained high proportions of well-drained soils, and 5-7% grassland habitat within 50 m were at greater risk for vole damage, especially if winter snow cover was minimal. Increased levels of vole damage also were found in fields containing a greater number of vole burrows and denser plant cover during spring surveys. Farmers may survey fields for vole sign and evaluate field attributes and weather conditions to identify where and when vole damage is likely to be greatest. They may reduce in-field vegetative cover, expand permanent grassland habitat at field edges to cover >7% of land area within 50 m of the field, plant cover crops that do not provide ideal forage, or apply conservation tillage to reduce habitat suitability of cover-cropped fields for voles before planting the commodity soybean crop.