Keep on the watch for downy mildew, as the continuing rainfall events followed by periods of dew in lettuce fields will maintain environmental conditions favorable for disease development. Evidence of downy mildew is the appearance of one or more angular lesions on leaves (yellow on the upper leaf surface and a white downy appearance on the lower leaf surface). As we move towards the end of this lettuce production season, powdery mildew can also occur. Powdery mildew begins as very small spots of white fungal growth on upper and lower leaf surfaces. The downy and powdery mildew pathogens both produce massive amounts of spores that initiate new infections. If fungicides are used, early initial application is essential for effective disease management. Contact me for effective fungicides to combat each type of 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.