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AbstractPowdery mildew occurs annually on melons in Arizona. Podosphaera xanthii (Sphaerotheca fuliginea) is the plant pathogenic fungus that causes powdery mildew on cucurbits, such as cantaloupe, honeydew, watermelon, cucumber and squash. Development of powdery mildew on melons is favored by moderate temperatures and relative humidity, succulent plant growth and reduced light intensity brought about by a dense plant canopy. Existing products as well as some materials under development were evaluated and compared for efficacy in management of powdery mildew on cantaloupe in a field trial conducted during the spring of 2004 at the Yuma Valley Agricultural Center. A high level of disease had developed by the time this trial was terminated (June 10). Among treatments, the degree of powdery mildew suppression ranged from modest to essentially complete control. All treatments significantly reduced the severity of powdery mildew compared to untreated plants. Relative performance of treatments on the top of leaves differed from that on the underside of leaves. The better treatments among all tested fungicides included Bravo Ultrex, Cabrio, Cabrio alternated with Procure, Flint alternated with Bravo, Microthiol Disperss, Procure, Procure alternated with Quinoxyfen, Quinoxyfen, Quinoxyfen alternated with Topsin M, Rally, Topsin M+Microthiol Disperss, and Topsin M alternated with Cabrio. Among tested products, several are registered for use in Arizona for control of powdery mildew on melons. The use of a mixture or rotation among efficacious chemistries with different modes of action is important to minimize the development of insensitivity by the pathogen to one or more of these active ingredients.
Series/Report no.Series P-139