- Bacterial spot can be a devastating disease when the weather is warm and humid.
- The disease can affect all above-ground parts of tomato and pepper plants: stems, petioles, leaves, and fruits.
- Fruit spots commonly result in unmarketable fruit, not only for fresh market but also for processing because the spots make the fruit difficult to peel.
Four closely related bacteria: Xanthomonas vesicatoria, X. euvesicatoria, X. gardneri, and X. perforans.
Different strains infect either tomato, pepper or both crops.
Signs and symptoms
- Tomato leaves have small (<1/8 inch), brown, circular spots surrounded by a yellow halo.
- The center of the leaf spots often falls out resulting in small holes.
- Pepper leaves have small (<1/8 inch), brown, circular spots that do not have a yellow halo and centers do not fall out.
- Small, brown, circular spots may also occur on stems and the fruit calyx.
- Fruit spots are ¼ inch, slightly raised, brown and scabby.
- Tomato fruit often have a waxy white halo surrounding the fruit spot.
- Pepper fruit spots often occur on the stem-end of the fruit.
- Spots occur on green and red fruit but do not result in rot.
- High temperatures (75°F to 86°F)
- High humidity
- Frequent rainfall/overhead irrigation
Biology and disease cycle
- Bacteria survive on plant debris in the soil for one to two years, but will not survive once plant debris is broken down.
- Introduction is primarily on infected seed or infected transplants. Even seedlings that do not show symptoms may be infected and will show symptoms later in the growing season.
- Bacteria can spread from plant to plant by tools, workers’ hands, or through splashing rain or irrigation water.
- Between rotations, the bacteria may survive on tomato or pepper volunteer plants.
Varieties with resistance to bacterial spot are available. There are many varieties of bell pepper and hot pepper with resistance to bacterial spot. A few tomato varieties with resistance are available.
- Purchase high quality, certified disease free seed if possible.
- Hot water treatment can be used to kill bacteria on and in seed.
- For growers producing their own seedlings, avoid over-watering and handle plants as little as possible. Disinfect greenhouses, tools, and equipment between seedling crops with a commercial sanitizer.
- For growers purchasing transplants, buy plants from reputable growers who start with clean seed and use good cultural practices to reduce disease.
- Once plants are in the field, avoid overhead watering
- Do not work in plants when wet to avoid spreading disease.
- Avoid high-pressure sprays, as these may injure leaves enough to encourage the introduction of the bacterial pathogen.
- Disinfect pruners and other tools by dipping in a commercial sanitizer, or a 1:9 dilution of germicidal bleach. To be efficient when pruning, have two pruners and alternate between plants to allow proper soaking time.
- Bury or remove crop debris at the end of the season.
- Rotate away from tomato or pepper for a year. It is important to control tomato or pepper volunteers during that time.
Pesticides are available to protect tomatoes and pepper from bacterial spot. Applications should be made when environmental conditions favor disease to be the most effective and repeated according to label instructions.
For a current list of pesticides for bacterial spot management visit the Midwest Vegetable Production Guide.
Reviewed in 2016