Leaf mold occasionally appears in high tunnel or greenhouse tomato production in New Jersey. However, under ideal conditions, the disease will develop in field-grown crops. The fungus will cause infection under prolonged periods of leaf wetness and when relative humidity remains above 85%. If the relative humidity is below 85%, the disease will not occur. Therefore, the proper venting of high tunnels and greenhouses on a regular basis is important. The pathogen can survive (overwinter) as a saprophyte on crop debris or as sclerotia in the soil. Conidia (spores) of the fungus can also survive up to one year in the soil.
Leaves of infected plants will develop pale green or yellow spots that are distinct. A dense, olive-green to brown spore mass will develop on the undersides of infected leaves.
Management of leaf mold begins with recognizing early symptoms, applying preventative fungicides, removing all infected plant material from the field, greenhouse, or high tunnel, and crop rotation. Protectant fungicides such as chlorothalonil used in weekly protectant spray programs will help control leaf mold. For organic growers, regular copper applications may help to suppress the disease.
For more information on options for controlling leaf mold in high tunnels and greenhouses, please see Table E-11 in the 2022/2023 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.
Source: plant-pest-advisory.rutgers.edu