Efficacy of Fungicides for Management of Powdery Mildew on Cantaloupe in 2005

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. 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 2005 at the University of Arizona Yuma Valley Agricultural Center. A high level of disease had developed by the time disease severity data was recorded (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 upper leaf surface differed from that on the underside of leaves. The best treatments among all tested fungicides included Quintec, Pristine, BAS517, Procure and Topsin M + Microthiol Disperss. Good levels of disease control were also achieved by Rubigan and Cabrio. The number of marketable cantaloupes was significantly higher in plots where powdery mildew was well controlled compared to untreated plots. Among tested products, several are registered for use in Arizona for control of powdery mildew on melons. Using a mixture of products or rotating among efficacious fungicides with different modes of action is important to minimize the development of insensitivity by the pathogen population to one or more of these active ingredients.