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Sclerotinia drop on lettuce is caused by two soil-borne fungi, Sclerotinia minor and S. sclerotiorum. This disease is favored by moist soil and moderate temperatures. Some registered products as well as new chemistries in development were compared for their ability to suppress Sclerotinia drop on lettuce during the winter vegetable growing season in 2006-2007. Sclerotia of each pathogen were incorporated into plots after lettuce thinning and just before the first application of test compounds. In plots infested with S. minor, Sclerotinia drop was reduced most effectively by some of the treatments containing boscalid, (Endura), fluazinam (Omega), Coniothyrium minitans (Contans), potassium silicate (Silmatrix), and polyoxin D (Endorse), where disease reduction compared to untreated plants ranged from 34 to 53%.. In plots infested with S. sclerotiorum, disease was reduced most effectively by application of iprodione (Rovral) and Omega followed by cyprodinil+fludioxonil (Switch), where Sclerotinia drop reduction compared to untreated plants ranged from 40 to 52%. Several other treatments provided significant but lessor degrees of disease control in the presence of S. minor and S. sclerotiorum. Two applications of the biopesticide Contans significantly reduced disease in plots infested with either S. minor or S. sclerotiorum. There was no statistical difference in disease control for either pathogen between application of Endura at 50 or 100 gal/acre. Two applications of Endura resulted in significantly higher disease control compared to one application of this product for plots infested with S. sclerotiorum; however, there was no difference in plots containing S. minor. For a valid comparison of products for control of Sclerotinia drop of lettuce, it is important to compare the results obtained from more than one field study. The reader is urged to review previous studies in addition to this report to get an accurate picture of the relative efficacy of tested compounds for control of Sclerotinia drop. Fungicides are not the only tools available to growers to manage Sclerotinia drop. Cultural methods, such as soil solarization or soil flooding in the summer, as well as crop rotation, can greatly reduce the number of viable sclerotia in an infested field. Use of these cultural methods alone or in combination with fungicide treatments can result in dramatic reductions in the incidence of Sclerotinia drop of lettuce. |
