Data from our recently completed 2018 head lettuce powdery mildew fungicide evaluation trial have been collected and analyzed. This trial consisted of 25 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 74% of leaves on nontreated plants contained powdery mildew at plant maturity. In comparison, plants treated with Luna Sensation had no symptoms of disease. Other strong performing fungicides included Merivon, a numbered product, and Quintec, which held powdery mildew to 2, 3, and 6% of leaves, respectively. In comparison, about 38% of leaves contained powdery mildew on plants treated with a biologically based material currently in development. In a 2017 lettuce powdery mildew trial, no powdery mildew was found on lettuce treated with Luna Sensation, Merivon, or Quintec, demonstrating the high efficacy of these products in two separate field trials. These fungicides, along with Rally, have been highly effective against powdery mildew of lettuce in recent years. Long-term success in managing powdery mildew 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.