Association of powdery mildew and spider mite populations in apple and cherry orchards

Abstract

Evidence is presented that shows densities, incidence, and reproduction of spider mites were greater on apple and cherry leaves infected with powdery mildew than on healthy leaves collected from orchards. In five apple and sour cherry orchards in 1996–1998, leaves infected with powdery mildew were more frequently infested with spider mites and mite densities were greater than on leaves without mildew. It appeared that spider mites colonized leaves after the mildew was present, but the mechanisms involved in this interaction are not known. In addition, laboratory experiments were conducted to evaluate the influence of cherry powdery mildew on reproduction of spider mites. Spider mite reproduction was enhanced by the presence of powdery mildew on detached sour cherry leaves in one laboratory trial, and the trend was similar in two other trials between 2 and 4 days after inoculation with mites. Mite reproduction did not differ between mildew treatments on later observation days (5 or 6 days after inoculation with mites) probably because of senescence and desiccation of the detached leaves. These findings may indicate that effective management of powdery mildew could reduce the need for acaricides and reduce the incidence of outbreaks of spider mites.