Grape erineum mite: Postharvest sulfur use reduces subsequent leaf blistering

The occurrence of eriophyid mites (Calepitrimerus vitis [rust mites] and Colomerus vitis [erineum mites and bud mites]) in vineyards worldwide is associated with leaf deformation, stunted shoot growth and reduced yield potential. In the North Coast region of California, leaf blistering by the erineum strain of Colomerus vitis is the most widespread symptom of eriophyid mite damage. Unlike rust and bud mites, erineum mites are generally considered a nuisance pest that is incidentally controlled by sulfur-dominated management programs for powdery mildew. However, recent reductions in the use of sulfur have allowed erineum mite populations to expand, highlighting the need for alternative management options. In this study, we posited that, during autumn, mites moving to buds from erinea (leaf blisters) to overwinter could be susceptible to sulfur applications. During four growing seasons, we documented patterns of mite movement to identify key sulfur application timing. We found the greatest numbers of migrating erineum mites from late September to early November. Concurrently, in replicated trials, we evaluated the efficacy of postharvest sulfur applications to reduce blistering. Sulfur applied during the migration period in 2013 appeared to eradicate leaf blistering in the 2014 growing season. In subsequent trials, sulfur treatments reduced blistering to less than 10% incidence, compared to 40% to 50% incidence in control plots.