Brown spots on tomatoes

Asked July 18, 2016, 2:57 PM EDT

All of my tomatoes are developing these brown spots. I can't find any photo online that resembles what I'm seeing. Any suggestions?

Clinton County Michigan

1 Response

This appears to be bacterial spot, which affect the leaves and fruits of both tomatoes and peppers, usually due to moist, humid conditions. Fruit spots are conspicuous on green fruit and appear raised and scabby, brown in color, circular, surrounded by a yellow halo, and are up to 1/3 on an inch in diameter. Spots on ripe fruit are similar except that they are sunken. Spots can appear on both leaves and fruit, but they are most commonly found on fruit.

Control of bacterial spot is difficult once it becomes established in a tomato planting. The pathogen that causes this disease may be introduced on infected seeds or transplants. It can survive up to a year on plant debris that was infected the prior year. It becomes active once temperatures heat to the 80s and 90s, and when several hours of moist conditions occur. The bacteria are splashed onto leaves and fruit, causing infections. If conditions stay moist, new infections will continue until the plants are removed.

Good sanitation (removing weeds and all plant debris at the end of the season), mulching (to prevent water splash from the soil), Irrigating from the ground (to limit foliar wetness), pruning to promote good airflow, staking plants up from the ground, and removing the lowest leaves on the plants is important. Remove and destroy diseased crop debris or incorporate it into soil soon after harvest is complete. Rotate tomato planting's with crops other than tomato and pepper to avoid carryover of bacteria from year to year. Using drip irrigation reduces bacterial spread and the leaf wetness periods that favor infection compared to sprinkler irrigation. Avoid working in plantings when foliage is wet. Intensive spraying of bactericides (mixtures of copper + fungicide) may reduce disease development.

I hope this was helpful. Feel free to contact us again if you have further questions.