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Summer Preplant Soil Flooding as a Management Tool for Sclerotinia Lettuce Drop (Jul. 13, 2011)

Lettuce disease management is probably the last thing on a Pest Control Advisor or growers mind as we now enter the hottest part of the year in the desert southwest. However, this is the perfect time to perform preplant soil flooding in fields that had high levels of Sclerotinia drop this past season. How can flooding of soil help manage a disease that will not be a problem for several more months? First of all, the two fungi that cause lettuce drop, Sclerotinia minor and Sclerotinia sclerotiorum, carry over in fields between crops of lettuce as structures called sclerotia. These fungal propagules function like seeds, remaining dormant until they germinate in cool moist soil and infect lettuce plants. Many sclerotia in soil decay naturally over time; however, sufficient numbers can remain in a field after one or more years to cause lettuce drop when a planting is established. If virtually all sclerotia in a field could be destroyed, then this field would no longer be a source of the Sclerotinia lettuce drop pathogens. This is where summer preplant soil flooding comes in. Past research conducted at The University of Arizona Yuma Agricultural Center demonstrated that a 3-week period of flooding in the summer destroyed all sclerotia of S. minor and S. sclerotiorum present in soil. Some growers in the Yuma area have used this procedure to help manage lettuce drop in fields chronically affected by this disease. For more information on this topic, please read the complete research paper on Plant Disease Vol. 89, No. 1.

Soil Flooding Yuma AZ

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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.

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