Anthracnose on Tomatoes

This fungal disease is a frequent problem in the latter part of the growing season, specifically on ripening tomato fruit. Anthracnose results in a fruit rot that reduces the quality and yield of tomatoes. The symptoms of this disease first appear as small circular, slightly sunken lesions on the surface of ripening fruit. The spots quickly enlarge becoming bruise like depressions that develop a water-soaked appearance beneath the surface of the skin. Soon after black concentric rings consisting of numerous small fruiting structures form in the center of the lesions. This disease is common during warm, humid weather after a rain or over head watering where the spores splash onto the fruit from the ground. Disease development is favored by temperatures over 80 degrees.

There are several cultural practices that can help reduce the incidence of anthracnose. Try to mulch around your tomatoes to prevent the splashing of spores from the soil. You should also provide support for your tomatoes either with cages, stakes or trellises to increase air movement and decrease the likelihood of favorable environmental conditions for infection. Use soaker hoses or drip irrigation to prevent the splashing of the spores onto the fruit from overhead watering (there is only so much we can do with rain.) Remove any infected fruit as soon as you notice the damage.

If you have had issues with anthracnose in the past you can apply preventative sprays, once the fruits are infected it can’t be saved. Spray options include the active ingredients Bacillus subtilis, chlorothalonil, copper fungicides, or maneb. Be sure to read the label to check the post-harvest interval (how long after you spray before you can harvest the fruit) and make sure it is labeled for anthracnose and the vegetable you are spraying.

Have questions? Contact our office where our Horticulture Extension Agent will assist you with questions.

Phone: (316) 321-9660

Email: callae@ksu.edu