White Mold in Hydroponic Lettuce

White mold is a disease caused by a fungal pathogen (Sclerotinia sclerotiorum). Although greenhouse food crops can become infected by this pathogen, it is uncommon and readily avoidable. For greenhouses at risk, cool, moist conditions favor disease development; however, microenvironments created by dense plant canopies such as hydroponic lettuce crops can also promote disease. In lettuce, white mold infection is also referred to as lettuce drop. Lettuce plants infected with white mold will become wilted and develop a white cottony growth or mycelium on the surfaces of leaves or the crown. The cottony mycelia (hyphae) can also cause light brown water-soaked lesions on the leaves and stems. Over time, the cottony mycelia will appear as clumps of mycelium on the leaves or crown and develop into small, irregular-shaped, hard, black sclerotia. If white mold infection is suspected, growers should submit plant samples to your preferred diagnostic lab to verify the cause of plant disease and obtain the latest management information. Greenhouse growers should scout the crop, rouge and discard infected plant material, and strive to limit moisture and humidity by venting and increasing the air circulation. For chemical control options, consult with your state greenhouse Extension educator(s) or specialist(s) or preferred diagnostic lab for options of registered fungicides to control white mold in hydroponic crops. To learn more about white mold in lettuce and common diseases of hydroponic leafy greens, refer to:

• e-GRO Edible Alert 6-16: Stop the Drop in Greenhouse Lettuce Production
• e-GRO Edible Alert 7-1: Common Diseases of Hydroponic Leafy Greens and Herbs
• e-GRO Edible Alert 7-6: Root Disease Management in Hydroponic Systems

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