Anthracnose is a group of fungal diseases caused mainly by Colletotrichum species. On tomatoes, it most commonly attacks ripe or ripening fruit, producing small, sunken circular spots that enlarge and darken. Under moist conditions, the centres may develop masses of pinkish or salmon-coloured spores.

The fungi can survive in infected plant debris and seed and may infect fruit while it is still green without producing obvious symptoms until the fruit begins to ripen. Spores spread primarily by splashing water, and warm, wet conditions favour infection.

How to Fix It

Remove infected fruit promptly and dispose of diseased plants and fruit at the end of the season. Rotate tomatoes and other susceptible crops with unrelated plants and avoid saving seed from infected fruit.

Water at soil level, mulch beneath plants to reduce soil splash, stake or cage tomatoes so fruit doesn't rest on the soil, and provide good airflow. Harvest ripe fruit promptly, particularly during wet weather.

Some Bacillus- and Trichoderma-based biological fungicides may help suppress anthracnose when used preventively, but they won't cure infected fruit. For the home garden, sanitation, reducing water splash and keeping fruit off the soil are the most useful controls.