Leaf mold, caused by the pathogen Fulvia fulva (Cladosporium fulvum, is primarily a disease of greenhouse tomatoes although it can occur in the field during cool, humid conditions. Most serious under humid greenhouse conditions and in poorl ventilated plastic houses, the fungus infects plants grown in soil as well as in hydroponic production. Tomato is the only plant affected by this disease. The actual relationship between disease severity and yield loss is still unclear. However, in one study, significant decreases in yield were detected 6 weeks after 50% of the foliage was symptomatic. The pathogen survives in the tomato field: — as a saprophyte on crop residue or as conidia or sclerotia in soil — as conidia or spores (can survive at least one year without a host or under adverse conditions) — as a contaminant of seed.
Symptoms usually only occur on the foliage. Older leaves are infected first and the fungus moves progressively up the plant on the younger leaves. Initial leaf symptoms appear as pale yellow or green areas or spots with indefinite margins. These are often first visible on the upper leaf surface. When infection is severe, these spots can coalesce and the entire leaf is killed. Diagnostic symptoms develop on the lower leaf surface when the fungus sporulates and gives the infected area an olive-green, velvety appearance. Infected leaves eventually brown, curl, wither, and drop prematurely. Defoliation gradually progresses up the plant as the fungus spreads to younger leaves. Symptoms can occasionally develop on petioles, stems, peduncles, blossoms, and fruit. Infected blossoms are usually killed before fruit set. Green and ripe fruit can be infected and develop a dark, leathery rot on the stem end. Infected fruit may also be lopsided and have blackened furrows. Climatic conditions for Disease Development: x) relative humidity levels >85%
x) free water on leaf surfaces
x) optimum temperature: 22-24 °C (germination occurs 5-35 °C) In FieldClimate.com we determine the risk of a Cladosporium fulvum infection by leaf wetness, relativ humidity and air temperature parameters. The graph shows an infection of tomatoes on the 22th of April.