Additional Comments on Summer Preplant Soil Flooding as a Management Tool for Sclerotinia Lettuce Drop (August 6, 2014)

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 virtually 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 situations. 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 examine and possibly refine 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. A research trial currently in progress 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.