Peppers are commonly grown in the backyard garden but they present certain challenges as they are highly susceptible to a number of diseases. Bacterial spot is among them. Bacterial spot affects both tomatoes and peppers, primarily sweet peppers. The disease is particularly destructive in zones where temperatures are high and rainfall is frequent. Treatment is very limited once the disease sets in. Most treatments are only effective if the disease is caught and treated early.
Bacterial spot is a disease caused by the bacterium Xanthomonas campestris subsp. Vesicatoria. It displays pale green spots on the underside of leaves while the top side shows a depression. As the disease progresses, the spots turn gold with brown edges. Further progression causes the center of the spot to die and disintegrate. Serious infection causes the defoliation and sun scald to exposed fruit. Symptoms on the fruit appear as light green, soft lesions. Other bacteria or fungus enter and cause fruit rot.
Preventive Seed Treatment
As the bacteria that cause bacterial spot can live in dormant seeds, there is cause to treat seeds before planting. There are two methods recommended for seed treatment. The first is a thorough rinse in hot water can kill the dormant bacteria on and inside the seed. Current recommendations suggest a water temperature of 122 degrees Fahrenheit for 25 minutes followed by immersion in cold water to slow the heating of the seeds. Heat may damage the seeds ability to germinate.
An alternate seed treatment method is sodium hypochlorite commonly known as bleach. Bleach only kills surface bacteria however, not bacteria that may be inside the seed. Cornell University recommends mixing 24 ounces of bleach with 1 gallon of water. Soak one pound of seed in 1 gallon of the solution for 40 minutes then rinse for 5 minutes with cold water. Seeds should be allowed to completely air dry before planting.
Bactericides containing copper or copper itself have some benefits in slowing the spread of the disease. Copper or copper sulfate is available under many name brands. The manufacturer's directions should be adhered to in terms of applications. Most recommend a five- to seven-day application cycle throughout the growing season to control or prevent bacterial spot.
Streptomycin is an antibiotic used to treat bacterial infections and is applied in spray form. It is only recommended for use on transplants going from the greenhouse into the field. If signs of the disease are present on seedlings prior to transplant, the plants should be segregated and should be treated separately before being transplanted outdoors.
Bacterial spot is a microscopic bacteria prevalent during periods of high relative humidity of 85 percent or more. If this condition occurs for several days, and moisture remains on plant leaves, the symptoms of the disease begin to appear. It spreads from plant to plant by the splashing of rain water or through the handling of plants when they are wet.