What to Do About Anthracnose on Tomatoes

Causal Agent

• Anthracnose affects the ripe and over ripe fruit. The fungal disorder is caused by a number of Colletotrichum fungi, namely C. coccodes. If not controlled in time, the disease can rot a full crop within a few days of infection under optimal weather conditions.

Favorable Conditions

• The fungus causing the disease is active at 68 to 75 degrees Fahrenheit. The organism overwinters within the soil, seed and infected debris around the plant. Keeping plant area clear of weeds and debris helps reduce chances of infection. Fungal spores are transmitted by early spring rains and overhead irrigation. Extended periods of moisture on fruit and foliage favor disease development.

Symptoms

• Tomato anthracnose starts with the appearance of water-soaked, small, sunken round spots that gradually keep increasing in diameter and depth. Spots start to appear within six days of infection. The central area of the legion starts to darken and shows dark, small, fruiting bodies or reproductive structures of the fungus. The lesions merge to create large rotted areas and entire fruit is decayed, inviting secondary pests. Unripe infected fruit reveals symptoms upon ripening.

Control

• Plant tomatoes in well-drained soil and practice crop rotation to minimize the growth of fungi in the soil. Avoid the use of overhead irrigation as the wet foliage is susceptible to numerous foliar disorders. Start the use of fungicides as soon as the first symptoms appear on fruit. Don't let fruit get overripe on the plant. Use certified, disease resistant seed. Recommended fungicides include mancozeb, boscalid, chlorothalonil, azoxystrobin or pyraclostrobin.