Management of powdery mildew (Podosphaera xanthii) on greenhouse cucumber in Ontario

Abstract

Cucumber powdery mildew (Podosphaera xanthii) causes significant annual yield and quality losses in greenhouse production in Canada. Management of the disease was evaluated in various research trials conducted at Harrow, ON from 1999–2007 and at two commercial greenhouse operations in Leamington, ON in 2005–2006. Products evaluated included biological control agents, new classes of fungicides, and materials derived from natural products as well as several traditional fungicides with multi-site modes of action. Best control in the research greenhouse was obtained with applications of Nova, Quintec, strobilurin derivatives (Quadris, Flint, Sovran), Procure, Pristine, JMS Stylet-Oil®, V-10118, Prev-AM, copper soap, Actigard and sulphur. Disease control was also obtained with Milstop, two fermented milk by-products (Lactosan, Yo-K-San) + surfactant formulations (Agral 90), and Agral 90 only. Applications of K2HPO4 + Agral 90, CaCl2 + Agral 90, and Siliforce were significantly better than the water check while fumed silica was not effective. Among biological control products, Sporodex (Pseudozyma flocculosa) was effective in control of P. xanthii while Serenade (Bacillus subtilis) was not. Actinovate (Streptomyces lydicus) provided control also. Under commercial greenhouse conditions, Milstop, and Lactosan + Agral 90 when applied weekly suppressed powdery mildew development at least equal to that of Nova. Resistance in P. xanthii to high rates of Nova and Pristine was detected in 3 of 17 and 2 of 8 commercial greenhouse cucumber operations, respectively, near Leamington. None of the locations had resistance to both fungicides at commercial rates of application, although one site showed consistently greater resistance of P. xanthii to both fungicides.