By Gene McAvoy
Bacterial spot of pepper, (Xanthomonas euvesicatoria) symptoms appear as small, water-soaked greasy spots on infected leaflets, which may coalesce. Fruit lesions appear blistered. In pepper, leaflet infection is most concentrated on older leaves and defoliation may occur in severe infections. Positive diagnosis requires lab tests as other diseases may cause symptoms that appear similar to those of bacterial spot.
Survival And Spread
Infection occurs through stomata or wounds made by wind-driven soil, insects, or cultural operations. Most inocula comes from volunteers or infected plant debris in the soil. Temperatures of 75°F to 87°F are ideal for bacterial spot, but infections can occur at higher or lower temperatures.
An integrated approach is needed to manage this disease. Sanitation is important. Volunteers and solanaceous weeds should be destroyed between crops. Transplant houses should be located away from tomato or pepper fields and only disease-free transplants and seed should be planted. Keeping infected plants out of the field is a grower’s first line of defense. Workers and farm equipment should be kept out of fields when fields are wet because the disease spreads readily under wet conditions.
Researchers have identified at least 11 different races of Xanthomonas euvesicatoria. Since no variety incorporates resistance to all races, it is important growers be knowledgeable about locally occurring races and use varieties that have resistance to races in their area. Bacterial spot race 1, 2, and 3 resistant pepper varieties have been used in Florida for many years. Over the past few years, seed companies have introduced several new varieties which incorporate additional resistance to races 4, 5, and 6. These 1-5 and 1-6 resistant varieties have shown excellent resistance and performance in the field.
It’s important to apply sprays before and during rainy periods. If conditions are favorable, frequent spraying may not be sufficient to maintain bacterial spot below damaging levels. The traditional recommendation for bacterial spot control consists of copper sprays. The effectiveness of copper is limited, because of the widespread occurrence of copper tolerance among strains. In the past, copper was tank mixed with maneb to increase efficacy against copper resistant strains. The Maneb label has been pulled, but Manzate ProStick (United Phosphorus Inc.) has received a label for this use on pepper in Florida.
Several products have given good results in research trials when used in rotation with traditional controls. These include Actigard (acibenzolar-S-methyl, Syngenta — chili pepper only), Tanos (famoxidone and cymoxanil, DuPont Crop Protection) as well as Quintec (quinoxyfen, Dow AgroSciences) and Serenade (QST 713 strain of dried Bacillus subtilis, AgraQuest).
Also, a number growers and researchers have experienced success with the bacterial virus AgriPhage (Omnilytics) for control of bacterial spot. Some growers also have reported good results using Oxidate (hydrogen dioxide, Biosafe Systems) as a sanitizing agent.
Gene McAvoy is regional vegetable extension agent IV with UF/IFAS.