By Mike Matheron, UA Extension Plant Pathologist

Melon growers need to keep in mind that powdery mildew can occur on fall melons in the desert.

If you have dealt with powdery mildew on spring melons, you will recall that powdery mildew starts off as very small colonies that may be few in number. However, they will continue to grow and produce ever larger quantities of spores, which in turn initiate more infections to bring about a rapid increase in disease symptoms.

In recent fungicide evaluation trials, several fungicides provided excellent control of powdery mildew including Microthiol Disperss (wettable sulfur) Quintec (quinoxyfen), Procure (triflumizole), Rally (myclobutanil), and Endura (boscalid). Thoroughly read the label for each product before use for critical information concerning the chemistry.

Effectively managing powdery mildew with fungicides is best achieved by initial application ideally before the first visible presence of the disease. Subsequent applications of fungicides throughout the life of the crop may be necessary.

The fungus responsible for powdery mildew on melons has developed resistance to some fungicides in the past. Maintaining long-term effectiveness of fungicides currently available requires resistance management strategies. One effective approach is to alternate among products with different modes of action.

The risk of powdery mildew on a particular melon planting is affected by the genetic susceptibility of the melon cultivar to the disease plus air temperatures during the growing season.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.