Management of powdery mildew on greenhouse cucumber (Cucumis sativus L.) plants using biological and chemical approaches

Abstract

Powdery mildew, caused by Podosphaera xanthii (U. Braun & Shishkoff), is a widespread disease on greenhouse cucumber in many countries, including Canada. The efficacy of seven biological or chemical products to manage powdery mildew was evaluated. These included Rhapsody® (Bacillus subtilis Ehrenberg strain QST 713), Microflora PROTM (B. subtilis, Bacillus amyloliquefaciens Priest et al., Bacillus pumilus Meyer & Gottheil), Prestop® (Gliocladium catenulatum J.C. Gilman & E.V. Abbott strain J1446), Double Nickel LC (B. amyloliquefaciens strain D747), Active Flower™ (fertilizer containing N:P:K of 8:4:12 plus 3% boron), Luna® (fluopyram and pyrimethanil) and Pristine® (pyraclostrobin and boscalid). Products were applied as preventative or eradicative treatments at weekly intervals to the moderately susceptible cucumber cultivars ‘Picowell RZ’ or ‘Tasty Green’. Disease severity was rated after 3–4 applications as the number of colonies that developed on leaves, or as a percentage of leaf area infected calculated using image analysis. Rhapsody at a rate of 1.5% provided the most significant disease reduction compared with the other three biological products, although rates of 2% and 4% also resulted in high disease suppression in a second experiment. The fungicides Luna (0.5 mL L−1) and Pristine (0.66 g L−1) provided a level of control comparable to Rhapsody. Application of ActiveFlower at 0.5 and 0.3 mL 100 mL−1 significantly reduced powdery mildew after three applications, but some phytotoxicity was observed at the higher rate. The products tested in this study can be part of an integrated powdery mildew management programme for greenhouse cucumber.