Heavy infections of powdery mildew have been reported in some melon fields in the Yuma Valley. This should be a warning to all melon growers in the area. Spores of Podosphaera xanthii, the fungal pathogen that causes powdery mildew, germinate at temperatures ranging from 72 to 88°F. Once germination has occurred, the fungus grows on the plant and can begin to produce spores 4 days later, continuing to do so until the plant tissue dies. This short generation time can lead to a rapid increase in disease when the plant canopy is well developed and melon fruit are developing. Also, remember that by the time you can actually see some powdery mildew in a field, many more emerging but invisible infections are already present. Successful management of powdery mildew involves initiation of a fungicide application program before or at the very latest at the very first appearance of powdery mildew. Contact me for more information concerning management of powdery mildew.

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.