Comparison of Row Cover Systems for Pest Management in Organic Muskmelon in Iowa

Abstract

Organic growers of cucurbit (Cucurbitaceae) crops in the midwestern United States have difficulty managing bacterial wilt—a fatal disease with a pathogen (Erwinia tracheiphila) that is transmitted by striped and spotted cucumber beetles (Acalymma vittatum and Diabrotica undecimpunctata howardi, respectively). Registered organic insecticides lack effectiveness, and host plant resistance is rare in commercial cultivars of many cucurbit crops. Row covers are widely used as barriers to minimize pest access, but the spunbonded polypropylene fabric covering traditional low tunnels must be removed at bloom to prevent overheating and facilitate pollination, thereby exposing the crop for the rest of the season. “Mesotunnels”—nylon mesh fabric covering 3.5-ft-high hoops—provide more space than low tunnels and mitigate overheating. In field experiments at Iowa State University (Ames, IA, USA) during 2016–18, two variations of mesotunnels—full-season tunnels [with purchased bumble bees (Bombus impatiens) added for pollination] and part-season tunnels (with covers removed for 2 weeks during bloom to provide pollinator access)—were compared with low tunnels and a noncovered treatment for organic ‘Athena’ muskmelon (Cucumis melo) production. Based on scouting results, full-season mesotunnels required no insecticides and part-season mesotunnels averaged 0.6 spray per season compared with 1.0 and 5.0 sprays per season for the low-tunnel and noncovered treatments, respectively. Incidence of pest and disease damage was zero for the full-season mesotunnels, 5% to 22% for the part-season mesotunnels, and 37% to 70% for both of the other treatments. Marketable yield for the full-season mesotunnel treatment exceeded the noncovered treatment significantly each year, and mean marketable yields were greater numerically than for the other treatments. Both mesotunnel treatments had a marketable yield that averaged more than twice that of the noncovered treatment in each year. Economic analysis (partial budget and cost-efficiency ratio) indicated that mesotunnels were likely to be more profitable in Iowa, USA, than either the low-tunnel or noncovered systems, but also that the year-to-year differential among treatments in profitability could be substantial. Additional experiments are needed to evaluate the efficacy of these integrated pest management practices and their profitability at spatial scales representative of commercial farms.