Bacterial leaf spot
Xanthomonas campestris pv. vesicatoria
Tomato and pepper
Who am I?
Bacterial leaf spot is a common disease of peppers and tomatoes that occurs throughout the world and favors high humidity and warm weather conditions. Contaminated seeds and infected plant debris from previous seasons are common sources of infection. The bacteria enters plant tissues through stomates and hydathodes or through injured tissues. Symptoms will appear within a week if conditions are permissible. After bacterial leaf spot is introduced to the field, the bacteria can spread from plant-to-plant through splashing water, contaminated tools, and workers on the field.
The initial symptoms include the formation of water-soaked spots on foliage, which become dark with time. Lower leaves tend to suffer the most and fall from plants when infestations are high. Affected leaves might exhibit chlorosis, while the spots themselves are sometimes encircled with yellow halos. Small elongated, brown-black spots may develop on petioles and along the stems. As the disease progresses, the spots cover more of the foliage surface which eventually collides and creates large necrotic areas. The symptoms on the fruit manifest as small, brown irregular shaped scabs.
The sooner the better: It’s easier and more cost effective to overcome infestations by controlling bacterial leaf spot in its initial stage. Make it a routine to monitor the field regularly and search plants for the above symptoms on a weekly basis, especially during hot and humid periods.
As with any moisture-favoring disease, various techniques taken during crop growth can reduce the chances of infection and spread:
Sanitation: Plant debris must be removed during cultivation. Sanitize equipment that comes in contact with infected plants. Do not allow equipment or workers to pass through the field when foliage is wet.
Improve air circulation: Promote the drying of foliage and shorten the duration of wetting periods by introducing net curtain vented areas (in closed structures).
Proper soil drainage: The presence of standing water will promote the spread of bacterial leaf spot.
*Drip irrigation is preferable to other methods of irrigation since the practice of using overhead sprinkler irrigation systems can significantly contribute to spreading the disease.
Prevention is key when it comes to bacterial leaf spot. Consider applying preventative sprays when hot and humid weather conditions are expected. The following are generic names of products used in one or more parts of the world: potassium salts of phosphorous (phosphonic) acid\potassium phosphonates and copper-based products (cuprous oxide and copper hydroxide).
The number of applications needed will vary in accordance to the infestation level and the growth environment. Cultural measures must accompany chemical control.
Caution and careful notice should be taken when using any plant protection products (insecticides, fungicides, and herbicides). It is the grower’s sole responsibility to keep track of the legal uses and permissions with respect to the laws in their country and destination markets. Always read the instructions written on labels, and in a case of contradiction, work in accordance to the product label. Keep in mind that information written on the label usually applies to local markets. Pest control products intended for organic farming are generally considered to be less effective in comparison to conventional products. When dealing with organic, biologic, and to some extent a small number of conventional chemical products, a complete eradication of a pest or disease will often require several iterations of a specific treatment or combination of treatments.