Data from our recently completed 2019 head lettuce powdery mildew fungicide evaluation trial have been collected and analyzed. This trial consisted of 10 treatments containing conventional and biologically based fungicides applied solo for the duration of the trial so that relative performance of individual fungicide products could be determined. Approximately 69% of leaves on nontreated plants contained powdery mildew at plant maturity. In comparison, plants treated with Rally had no symptoms of disease. Other strong performing fungicides in the trial included Torino, Mirivis Prime, and Fontelis, which held powdery mildew to 12, 14, and 17% of leaves infected, respectively. In the 2017 field trial, Luna Sensation, Merivon, and Quintec were highly efficacious, completely preventing development of powdery mildew on head lettuce. The fungicides mentioned from these studies are all good candidates for inclusion in future fungicide application programs for effective management of powdery mildew. Keep in mind that long-term success in managing this disease can be accomplished by preserving the efficacy of fungicides currently available, which can be achieved by applying fungicides with different modes of action as mixtures or in rotation to delay development of pathogen populations resistant to the fungicides.

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.