Bacterial Spot Shows up on Peppers in Utah
In Utah, the symptoms of bacterial spot that we observed on peppers included small brown lesions on leaves and small, tan to black spots on fruits.
Bacterial spot of pepper and tomato, caused by Xanthomonas vesicatoria and X. euvesicatoria, is a disease that is commonly found in warm, moist regions that grow these crops, so it is not commonly found in Utah. The heavy rains in August 2014 in northern Utah, however, were prime conditions for an outbreak of bacterial spot, in particular on pepper.
The primary spread of bacterial spot is via seeds infected with the bacteria, while secondary spread can occur from one infected plant to another, or from infected debris left in a field. Transplants grown from infected seed may not show symptoms if they are grown in cool, dry conditions. The bacteria will remain latent until the plants are exposed to high temperatures and moisture through rain or overhead irrigation. Initial symptoms are small brown spots on leaves. Under warm and humid conditions, they can coalesce and form large blighted areas. On greenhouse-grown transplants, leaves turn yellow and drop prematurely. Black spots will also develop on fruit, which makes the fruit unmarketable. Once symptoms develop, splashing irrigation water or wind and rain can quickly spread the bacteria through the greenhouse or across a field.
Management of bacterial spot of pepper is difficult. The only chemical option is copper, which helps to stop spread of the disease from plant to plant. In many parts of the country, X. vesicatoria has become resistant to copper and treatments are ineffective. In Utah, we have not yet found resistant isolates of the bacteria.
There are cultural practices that can help to minimize this disease. Avoiding overhead irrigation can slow the spread of the bacteria. In addition, cull piles should be removed from adjoining pepper or tomato fields. Crop rotation after an outbreak is important because the bacteria can survive in infected plant debris. Peppers should not be rotated with tomatoes that are also susceptible to the pathogen. One year of rotation should be long enough.
The best management option is the use of disease-free seed and transplants. There is one pepper variety from Seminis Vegetable Seeds (PS 09942815 (with X10R™)) that has resistance to all ten races of the bacteria that are known to occur. Other pepper varieties are resistant to races 1, 2 and 3 (click here for more information). We currently do not know which race(s) we have in Utah.
- Claudia Nischwitz, Plant Pathologist