Cause Passalora fulva (syn. Fulvia fulva, formerly Cladosporium fulvum), a fungus. Spores resist drying and may survive in the greenhouse up to one year after plants are removed.This pathogen can also survive in soil as sclerotia and conidia. The fungus is most destructive when humidity is high (greater thean 85%); temperatures between 68°F to 75°F are optimum but disease can occur at cooler and warmer temperatures. The disease usually will not be severe if the relative humidity at the leaf surface is kept below 85%.
Symptoms White spots that rapidly enlarge and become pale green to 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. This fungus can also attack petioles, stems, blossoms, and fruit.
Cultural control
- Leaf mold can be kept under control if ventilation is ample and air circulation good in the houses.
- Stake and prune plants to promote air movement within canopy.
- 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).
- Remove and destroy crop residues.
- Treat seeds with a hot water treatment (122°F for 25 minutes) or use a chemical seed treatment listed under chemical control below.
Chemical control
- Seed treatment with sodium hypochlorite. Wrap seed in a cheesecloth bag and soak with agitation 40 min. in 1.05% sodium hypochlorite (1 part household bleach to 5 parts water). Spread out seed and allow to dry. Prepare fresh solution for each batch of seed.
- Affiance (Group 3 + 11) at 9 to 12 fl oz/A on 7- to 14-day intervals. Preharvest interval is 1 day. 12-hr reentry.