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What is it?
Tomato plant bacterial spot is a disease of xanthomonos vesicatoria, an invasive bacterium which attacks green tomatoes, but does not attack red tomatoes. This disease can result in severe tomato plant defoliation which will harm your vegetable garden crop of tomatoes.
What does it look like?
Xanthomonas vesicatoria appears on tomato plants in the form of 1/8 inch to 1/4 inch in diameter spots on the green tomato fruits. These small spots will be dark, brown to blackish, and are often raised and seem scablike. With tomato bacterial spot, you will find that these dark spots will also be sunken in their centers or toward the middle of the spots. Leaves of the tomato plant will also be affected, and may develop spots which can be up to 1/8 inch diameter which appear quite dark and will be greasy or oily feeling to the touch. These spots usually do not have sunken centers, however they will cause the leaves to drop off the tomato plant resulting in defoliation of the tomato plant. Extreme xanthomonas vesicatoria infection can result in losing all or almost all leaves from the infected tomato plant, and usually the infection of bacterial spot will spread to nearby tomato plants as well.
How does it manifest?
Tomato bacterial spot begins by infecting all part of the tomato plant which is above ground. Xanthomonas vesicatoria can infect tomato plants at any stage of their growth and development. You may notice that your blossoms are dropping off the tomato plants, resulting in reduced fruit yield of the tomato crop. The xanthomonas vesicatoria bacterium of bacterial spot enters the healthy tomato plants through small wounds in the surface of the tomato plant. Typically these wounds are caused by small insects who have fed on the tomato plant, rough abrasions from blowing sand in the wind which has come up against the tomato plant, or from mechanical injuries incurred during transplanting of the tomato plants or during harvest or cultivation. The bacterium is especially active when temperatures range from 75° to 85° F, and xanthomonas vesicatoria will multiply and spread most during wet seasons and rainy weather. When extreme infections occur, most often after heavy rains when the bacterium spreads quickly, it can weaken the plant and often results in severe defoliation which can expose the fruit to sunscald or prime them for a variety of rot organisms to infect them.
What can you do about it?
Tomato plants which show signs of bacterial spot damage need to be treated at seven day intervals with a fungicide which contains two ingredients. Be sure that the fungicide you choose to treat xanthomonas vesicatoria contains both maneb abd basic copper sulfate. You will also need to pick and destroy any affected green tomato fruits as these will be inedible. Keep repeating the treatments of fungicide as long as weather conditions favor it’s spread or you continue to see damage from the bacterium. In order to reduce the spread of xanthomonas vesicatoria, be sure to avoid overhead watering and do not work around the plants in wet weather. Be sure to destroy all plant debris at the end of the harvest so that the bacterium does not overwinter on seeds or plants. You may also want to check into disease-free plants your next planting season, or disease-free seeds. Be sure never to save the seeds of fruits which have been infected with bacterial spot as they are sure to spread the disease in your garden again when you plant them
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