Living mulch cover crops can improve soil health and build organic matter, yet their use in fruit orchards comes with a risk of encouraging meadow vole (Microtus pennsylvanicus), a rodent that can be destructive to fruit trees. Several living mulch cover crop species were assessed in an apple (Malus ×domestica) orchard understory along with wood chip mulch and bare ground. Desired species characteristics were weed competitiveness, low growth habit, nitrogen fixation, and potential rodent repellency. Legume species included birdsfoot trefoil (Lotus corniculatus), medic (Medicago spp.), and subterranean clover (Trifolium subterraneum), which were planted in solid stands as well as mixtures. Nonlegume species included sweet woodruff (Galium odoratum), sweet alyssum (Lobularia maritima), creeping thyme (Thymus serpyllum), and colonial bentgrass (Agrostis tenuis). Meadow vole presence was evaluated in fall and spring with point-intersect and run-length measurements. A legume mix (medic, birdsfoot trefoil, subterranean clover, and colonial bentgrass) had the highest meadow vole presence, with no reduction under the “sandwich” system of tilling either side of the tree trunks while leaving a cover crop in a narrow strip with the trunks. The nonlegume mix [colonial bentgrass, sweet alyssum, creeping thyme, and fivespot (Neomophila maculata)] had similar results. However, the sweet woodruff (planted in the “sandwich” system) had significantly lower presence of meadow voles than the other living mulches. Wood chip mulch, cultivation, and bare ground control were all similar, with very low presence, indicating low risk of meadow vole damage. The results from the sweet woodruff suggest that we need more research on the potential to select living mulches that are nonattractive or repellent to meadow voles for use in orchards.
Apple maggot (Rhagoletis pomonella) is an insect pest of apple (Malus domestica) that is currently limited in extent in the commercial production areas of Washington State thanks to a quarantine program. We estimate the costs to the Washington economy if this pest were to spread more widely. Apple maggot control costs are related to the pressure of codling moth (Cydia pomonella), the most prevalent insect pest in commercial apple production in Washington State. It was found that the losses for the Washington apple industry’s range from $510 million to $557 million, depending on the codling moth pressure. Our findings underscore the importance of an efficient quarantine program that minimized the risk of spreading the pest along with additional costs associated with quarantined areas.