Cause Passalora fulva (syn. Fulvia fulva, formerly Cladosporium fulvum), a fungus. Spores resist drying and may survive in the greenhouse several months after plants are removed. The fungus is most destructive when humidity is high (90% to 100% at the leaf surface) and the temperature is 65°F to 80°F. The disease usually will not be severe if the relative humidity at the leaf surface is kept below 90%.
Symptoms White spots that rapidly enlarge and become yellow appear on the upper surfaces of older leaves. The patches' lower surfaces become covered with a velvety, olive-brown fungus growth. When the disease is severe, much of the foliage is killed, and the crop is greatly reduced.
- Leaf mold can be kept under control if ventilation is ample and air circulation good in the houses.
- Maintain temperature at 60°F to 65°F, at least. Heat at night, when outside air drops below 60°F, to control humidity increases that come with lower outside air temperatures.
- Varieties reported resistant to some strains of the fungus include Santa Fe, Globelle (pink fruit), Bay State (red fruit), and Vetomold (red fruit).