Comparison of Products for Management of Powdery Mildew on Cantaloupe in 2003

Abstract

Powdery 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. When environmental conditions are favorable, disease incidence and severity can reach economically significant levels. 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 2003 at the Yuma Agricultural Center. A moderately high level of disease had developed by crop maturity (June 17) on untreated plants. 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. The best performer among all treatments in this trial was Procure at 0.25 lb a.i., which completely inhibited disease development. Several other treatments resulted in a low mean disease severity rating (1 to 5 mildew colonies per leaf), including Quinoxyfen+Actigard, Rally+Actigard, Flint alternated with Bravo, Microthiol Disperss, Bravo, Quinoxyfen, Rally, Flint alternated with Bravo, Flint+Reason+Bond, Topsin M, Quadris+Latron B-1956, Flint+Actigard, Flint, Topsin+Trilogy, Kaligreen+No Foam A, Quadris+Latron B-1956 alternated with Actigard, Quadris+Latron B-1956+Actigard, and Pristine. Multiple applications of a single compound are included in these trials to gather information on the relative efficacy of each separate chemistry over a multi-year period. 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 will help to inhibit the development of insensitivity by the pathogen to one or more of these active ingredients.