Along with concerns for virus and other pest problems, melon growers should also keep in mind that powdery mildew can occur on fall plantings. Similar to disease development in the spring and summer, powdery mildew first becomes apparent as very small colonies that may at first be few in number. However, these spots will enlarge and produce ever larger quantities of spores, which in turn initiate more infections and increase powdery mildew coverage of melon leaves. Compared to powdery mildew in the spring and summer, the rate of disease development may be slower on fall melons due to lower temperatures as plants progress to maturity. Past fungicide evaluation trials have shown that several registered fungicides can provide excellent control of powdery mildew, such as Fontelis (penthiopyrad), Microthiol Disperss (wettable sulfur), Quintec (quinoxyfen), Procure (triflumizole), and Rally (myclobutanil). Some new fungicides in development also provided outstanding control of powdery mildew, suggesting that additional effective compounds may be available in the future. Effectively managing powdery mildew with fungicides is best achieved by initial application before the first visible presence of the disease. Good levels of disease control also can be obtained by not starting applications until the first visible signs of powdery mildew; however, disease management success will decrease as the initial treatment is delayed and the disease becomes more established. The risk of powdery mildew within a particular melon planting will be determined by the genetic susceptibility of the melon cultivar as well as environmental factors during the time of disease initiation and development.

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To contact Mike Matheron go to: matheron@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.