Effectively managing powdery mildew with fungicides is best achieved by an initial application ideally before but no later than the first visible detection of the disease. Subsequent applications of fungicides are usually necessary throughout the life of the crop. Several products are highly effective in controlling powdery mildew, as demonstrated in yearly fungicide trials conducted at the University of Arizona Yuma Agricultural Center. One such trial completed in 2009 illustrates the comparative efficacy of several tested fungicides. Podosphaera xanthii, the fungus responsible for powdery mildew on melons, has developed resistance to some fungicides in the past, so maintaining long-term effectiveness of those materials currently available requires the use of resistance management strategies. One effective approach is to alternate among products with different modes of action. Two recent field trials evaluating treatment programs containing different fungicides and application sequences yielded very similar results. As shown in the most recent of these trials, completed in 2009, fungicide application sequences containing a highly efficacious fungicide alternated with a product of moderate to low efficacy provided a final level of disease control equivalent to that achieved by continuous application of the highly effective material. These data suggest that high levels of disease control and resistance management can be realized with fungicide alternation programs not only employing highly effective chemistries with differing modes of action, but also incorporating products with high efficacy along with those of moderate and low effectiveness.

To read the reports go to "Efficacy of Fungicides" and "Fungicide Application Programs".

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.