lettuce drop (Sclerotina)

Asked May 1, 2019, 12:02 PM EDT

Hi, I am a home aquaponics grower. I grow black-seeded simpson lettuce in raft beds year round. The water circulates through a 200 gallons of aquariums with dozens of catfish and guppies. The past couple of months my lettuce has been plagued by Sclerotina (lettuce drop). I am relatively certain this is the correct diagnosis as the rockwool cubes on which the lettuce grows have a black grainy substance growing on them. In addition the plants are dying in the prescribed way; outer leaves wilt, then the stem turns to a brown liquid gel. I am worried to hear that it is difficult to treat; especially in a way that is safe for our family. The temperature is a constant 72 degrees maintained by the constant temperature of circulating water underneath. thank you, John

Ramsey County Minnesota aquaponics fungal disease horticulture

1 Response

If there is a fungal contamination in your system the crop will need to be destroyed and everything broken down and sanitized. Fungicides can prevent fungal infections but cannot cure them. Fungal infections are hard to cure so it will require persistence and be labor intensive. Any component of the system that cannot be sanitized that has been in contact with infected plants should be replaced. Sclerotina and powdery mildew are both fungal infections and have similar symptoms. The treatment is the same. http://cea.cals.cornell.edu/attachments/Cornell%20CEA%20Lettuce%20Handbook%20.pdf Here is an excerpt on managing diseases in aquaponic systems growing lettuce. Disease Maintaining a healthy crop is vital. Powdery mildew can be a problem during winter production of lettuce. A plan should be in place for the treatment of mildew and appropriate chemical controls should be obtained before the crop is planted. The following are suggestions for maintaining a healthy greenhouse environment: Keep the crop rapidly growing by providing adequate light, nutrients, and other environmental conditions at all times. If root disease does occur, the ponds and solution tanks should be drained and the crop sacrificed. The ponds and tanks should be cleaned with a 2% bleach solution. Other sanitation products exist and are easily available such as Greenshield. It is possible the disease started in the Germination Area, and that area, including the benches and solution tanks, should be cleaned, as well. Wash the Styrofoam floats, trays, and other equipment with a 2% bleach solution. The equipment should be washed between each use, to prevent the spread of disease. Do not bring other plant material or soil into the greenhouse. This material may contain pests and pathogens likely to infect your crop. Keep visitors to the greenhouse to a minimum or allow them to view the production area from the outside of the greenhouse only. Keep the solution tanks shaded in some manner. Algae flourish in wet, well-lit locations, and the solution tank is ideal for algal growth. Shading the tanks, input and output pipes, and other "wet" equipment will inhibit algal growth. The algae will not harm the crop directly, but may act to weaken the crop to potential disease.