Figure 1. Anthracnose of tomato

Disease

Anthracnose is a frequent problem in the latter part of the growing season on ripening tomato fruit. The disease results in a fruit rot which reduces the quality and yield of tomatoes.

Symptoms of anthracnose appear first as small, circular, slightly sunken lesions on the surface of ripening fruits. The spots quickly enlarge, become deeply depressed, and develop a water-soaked appearance directly beneath the skin (epidermis) of the fruit. Black, concentric rings form in the center of the lesions; the rings actually consist of numerous small fruiting structures (acervuli) of the disease-causing fungus. During humid weather, masses of buff-colored fungal spores (conidia) are extruded from the fruiting structure. Several lesions may coalesce, causing extensive decay of the fruit. Eventually, secondary microorganisms invade the lesions and cause a complete rotting of the fruit.

Cause

The fungus (Colletotrichum coccodes) is capable of surviving in infected plant debris and in the soil.  During rainy weather, spores of the fungus are splashed onto the fruit. Most infection takes place on ripe or over-ripe fruit. Green fruit also may be infected, although symptoms do not develop until the tomatoes begin to mature. Disease development is favored by high temperatures (80° F) and frequent rainfall.

Control

Several cultural practices help reduce the incidence of anthracnose. Mulching around the tomato plants prevents splashing of inoculum from the soil onto the fruits. Staking tomatoes increases air movement and decreases the likelihood of favorable environmental conditions for infection. Avoid overhead watering and remove infected or rotting fruits from the plant. Follow a three year rotation with non-solanaceous crops. Deep plow or till tomato debris into the soil after the last fall harvest

Fungicides used for the control of Septoria leaf blight and early blight also are effective in reducing losses caused by anthracnose. Applications should begin after fruit begins to set on the plants.

Homeowner: Daconil, Fungi-Gard, Liquid Fungicide, Encore, Monterey Bravo

Others

Homeowner: Copper Fungicide, Bordeaux

Homeowner: Mancozeb, Maneb