Potential for Cultural Management of Lettuce Drop (Sclerotinia sclerotiorum) in High Tunnels Through Modification of Soil Moisture, Planting Date, and Cultivar

Lettuce is a high-value crop commonly grown in high tunnels. However, lettuce drop, caused by Sclerotinia sclerotiorum, can greatly impact lettuce production and profitability. Crop loss from S. sclerotiorum can be especially severe in high tunnels because of intensive cropping and limited options for non-host rotations. A study was conducted in a Kentucky high tunnel infested with S. sclerotiorum to determine if soilmoisture, planting date, and host resistance can successfully manage lettuce drop. The experiment was arranged in a split-split plot design with soil moisture (high: 60 to 100%, low: 40 to 80% plant available water), planting date (early, mid, and late spring), and lettuce cultivar (Galactic, Harmony, Pirat, and Vulcan) being the main plot, subplot, and subsubplot factors, respectively. In year one, lettuce drop incidence was significantly lower in the low soil moisture and early planting date, and significantly higher in Pirat lettuce. Marketable lettuce weight was significantly higher in the late planting and Vulcan treatments. In year two, lettuce drop incidence was significantly lower in the late planting and Galactic compared with all other treatments. There was no significant difference in lettuce drop incidence between the high and low soil moisture in year two. Harmony and Vulcan had significantly higher marketable weight compared with all cultivars. Planting date and lettuce cultivar had the strongest effect on lettuce drop incidence. Although midspring is considered the ideal time to plant lettuce in Kentucky, growers managing lettuce drop should consider planting earlier or later and selecting resistant cultivars appropriate for their markets.