New Fungicides Evaluated for Control of Powdery Mildew of Cantaloupe in 1998

Abstract

Powdery mildew of cucurbits, which include cantaloupe, honeydew, watermelon, cucumber and squash, occurs every year in Arizona. Moderate temperatures and relative humidity, succulent plant growth and reduced light intensity brought about by a dense plant canopy are factors that promote development of powdery mildew, which is caused by the pathogenic fungus Sphaerotheca fuliginea. 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 1998 at the Yuma Agricultural Center. A high level of disease had developed by crop maturity (June 23). On the upper leaf surface where spray coverage was good and disease severity on nontreated leaves was moderate (24% of upper leaf surface infected), all treatments significantly reduced the severity of powdery mildew. These treatments included Sovran, Flint, Procure, Topsin M, Quadris, Benlate, quinoxyfen, Rally, Trilogy, Actigard, Bravo, JMS stylet oil, Kaligreen and Bayleton. In contrast, on the lower leaf surface where spray coverage was not as good and disease severity on nontreated leaves was very high (94% of lower leaf surface infected), the best disease control was achieved with chemistries that have systemic properties. Treatments that held the infected lower leaf surface to 20% or less included Sovran, Flint, Procure, Topsin + Microthiol, and Quadris. 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.