Anthracnose Can Cause Red Alert For Tomato Growers

Disease Specs

Anthracnose is a sometimes serious disease of tomato, caused by several fungi in the genus Colletotrichum, including C. gloeosporioides, C. dematium, and most commonly C. coccodes.

anthracnose of tomato; diseases of tomato; crop protection

Photo courtesy of Clemson University

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Identification

Anthracnose is a disease of warm, moist climates. The pathogen may infect immature fruit, but symptoms do not appear until fruit matures and ripens. Infection can occur over a wide range of temperatures, but is favored by cool to moderate temperatures (68ºF to 75ºF) in the presence of free moisture.

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The fungus is a weak parasite and is primarily a disease of ripe fruit. Colletotrichum has a broad host ranges and causes disease on eggplant, pepper, and tomato, as well as other crops and weeds. The disease can cause severe problems in peppers, especially when fruit is allowed to go to color.

Spots on fruit are initially small, circular, and depressed. They enlarge over time, and may develop concentric rings. With age, the center of lesions darkens and becomes tan and dotted with small black specks as the fungus produces spore-containing structures (microsclerotia and acervuli). Dark, needle-like spines called setae surround the fruiting bodies that erupt through the plant tissue.

Masses of pink to orange spores are released when weather is wet or humid. These spores are dispersed to other fruit by splashing water. Eventually, the entire fruit may rot. Fruit nearest to the ground are more likely to be affected.

Infection also may occur on stems, leaves, and roots. Root infections become evident when fruit begin to ripen. Root lesions are brown and dotted with microsclerotia. The cortex of infected roots is often completely rotted.

Survival And Spread

Colletotrichum survives between crops on infested plant debris in the soil. Early in the growing season, spores from the soil splash on lower leaves of the tomato plant. Few symptoms develop on infected leaves, but the spores produced on foliage can be carried by splashing rain to developing green fruit. Infected green fruit will not develop symptoms of anthracnose until they begin to ripen. Ripe fruit are very susceptible to this fungus. The pathogen also can be seedborne.

Management Methods

Growers should manage anthracnose by controlling sources of the pathogen, minimizing the opportunity for dispersal of the pathogen, reducing favorability of environmental conditions for disease development, and applying fungicides. There are no resistant varieties.

Plant only high-quality seed and transplants free of infection. Practice at least a two-year rotation between susceptible hosts. Eliminate weeds, volunteers, and culls that might harbor the pathogen by deep burial. Staking plants and plastic mulching can reduce anthracnose losses as can irrigation practices that promote rapid leaf drying and reduce extended periods of leaf wetness.

Pick fruit as soon as it is ripe to minimize time for anthracnose to develop, but also note that development of symptoms is not completely prevented by moving fruit to protected, indoor conditions.

Fungicides are most effective when used in combination with cultural control strategies. Soil fumigation with broad-spectrum fumigants may help reduce soil inoculum.

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