Leaf Mold of Tomato
Dan Egel, Extension Plant Pathologist, Southwest Purdue Ag Center, Purdue University
I received an email this week from a grower entitled, “Leaf mold already!” It might seem to be a bit early for this disease, but the unseasonably warm weather might be the reason. Leaf mold, Fulvia fulva, (also known as Cladosporium fulverum) causes pale lesion
s on leaves that seem to be limited by major veins (Figure 1). When the leaves are turned over, the fungal mold that gives the disease its name becomes evident (Figure 2). Under humid conditions and temperatures between 72 and 75 degrees F, leaf mold may cause loss of plant vigor. Fruit are not generally affected. The spores produced on the underside of leaves are readily airborne and spread easily from leaf to leaf. Leaf mold is more common in a greenhouse or high tunnel, as in the case of the grower who contacted me this week, than in the field.
Tomato plants with resistance to leaf mold are available. However, the fungus is variable and may overcome resistance. Crop rotation can help to reduce plant residue. If tomatoes are grown year after year in the same location, remove as much of the plants and debris as possible from the field or greenhouse after the last harvest. Do not use composted tomato material for tomato production. Space plants appropriately and prune lower leaves to improve air circulation. Reduce humidity in greenhouses by venting the structure before nightfall. Fungicides are available to help manage leaf mold. The Midwest Vegetable Production Guide for Commercial Growers 2012 has information on what products are labeled for leaf mold of tomato and what may be used in a greenhouse setting. Homeowners may use products with the active ingredient chlorothalonil to help manage the disease (chlorothalonil may not be used in greenhouses).
Click image to enlarge
Figure 1. Top of leaf
Figure 2. Underside of leaf