As stated last time, research studies revealed that a 3-week period of field flooding during the hot summer months of July and August proved to be an effective cultural means of controlling Sclerotinia lettuce drop in future lettuce plantings, as this procedure destroyed all sclerotia of Sclerotinia minor and S. sclerotiorum in soil. During 2011 and 2012, over 4,200 and 3,600 acres, respectively, were subjected to preplant soil flooding in the Yuma Valley. However, some negative effects of this practice have been noted in certain circumstances. One concern is the rising of the ground water table, particularly in areas already affected by high ground water. Also, in certain areas in the Yuma Valley, damage to the open drainage system has occurred as a result of erosion of the sides of earthen drains. These concerns have led to the initiation of additional field research at the Yuma Agricultural Center to further define the method of water delivery and the duration of soil wetness required to destroy sclerotia of Sclerotinia minor and S. sclerotiorum. The goal of this research is to achieve destruction of the Sclerotinia lettuce pathogens in soil with the least amount of water possible. The research trial this summer will tell us if this is possible. Although summer soil flooding may not be appropriate for all ground planted to lettuce, this cultural practice can be an effective component of an integrated management program for lettuce drop.

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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.