| Summary: | Powdery mildew on melons is an annual disease problem in Arizona. Sphaerotheca fuliginea is the plant pathogenic fungus that causes powdery mildew of cucurbits, which include cantaloupe, honeydew, watermelon, cucumber and squash. When environmental conditions are favorable, disease incidence and severity can reach economically significant levels. Factors that favor development of powdery mildew on melons include moderate temperatures and relative humidity, succulent plant growth, and reduced light intensity brought about by a dense plant canopy. Potential new fungicides were evaluated and compared to existing chemicals for control of powdery mildew of cantaloupe in a field trial conducted during the spring of 1999 at the Yuma Agricultural Center. A high level of disease had developed by crop maturity (June 29). On nontreated plants 43% of the upper leaf surface was covered by powdery mildew, whereas the level on the underside of leaves was 78%.. All of the 34 different treatments significantly reduced the level of powdery mildew on both sides of leaves, compared to nontreated plants. The best treatments among those tested with respect to disease control on the underside of leaves, where disease control is more difficult than on the tops of leaves, included Topsin+Trilogy, Benlate, Benlate+Trilogy, Quadris, A815, Topsin+Microthiol, and Topsin. The potential availability of new chemistries for management of powdery mildew of cantaloupe and other cucurbits could help improve overall control of powdery mildew as well as the implementation of fungicide resistance management strategies, which strive to minimize the risk of resistance development by the pathogen to these compounds.
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