Melon powdery mildew

By Mike Matheron, UA Extension Plant Pathologist

It is not too early to begin considering management options for powdery mildew on melons. The disease generally is favored by dry weather conditions, moderate temperatures, reduced light intensity, fertile soil, and succulent plant growth. The overall risk of powdery mildew increases as more of these factors become established in a melon field.

Dry weather conditions and fertile soil are givens in desert melon production fields. Spores of the powdery mildew pathogen,Podosphaera xanthii, can germinate to initiate disease at temperatures ranging from 72 degrees to 88 degrees F., and optimally at about 82 degrees. These moderate temperatures, plus reduced light intensity and succulent plant growth, all become increasingly prevalent as melon plantings grow rapidly during April and May.

Another factor to consider when determining powdery mildew risk is the inherent susceptibility of the melon cultivar grown. The cultivars known to be very susceptible to powdery mildew require implementation of a rigorous disease management program involving applications of fungicides with differing modes of action throughout the period of high disease risk.

On the other hand, melon varieties with moderate to high levels of genetic resistance to the pathogen will likely require fewer fungicide applications.

To achieve maximum levels of disease control, powdery mildew fungicide application programs must be initiated before or at the latest at the very first sign of disease in the field. These initial infection sites are often on the underside of leaves. Frequent and comprehensive examination of the melon planting is required.

For more information watch the video Effective Management of Melon Powdery Mildew in the Desert Part I and Part II.

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