Disease guide

Symptoms can appear on all above ground parts of the plant. The first symptoms observed on the leaves are dark, water-soaked, circular spots that are less than 3 mm in diameter. These spots become angular and the surface may appear greasy with a translucent center and a black margin. The centers of these lesions soon dry and crack, and a yellow halo may surround the lesion. Lesions tend to be more numerous on the young foliage. During periods of high moisture (heavy rain, fog or dew) leaves will take on a blighted appearance rather that the typical leaf spots. Fruit infection begins as small, black, raised specks, which may be surrounded by a white halo that has a greasy appearance. These lesions can enlarge to 4-5 mm (0. 25 inch) in diameter and become brown, slightly raised and scabby in appearance. They can also have raised margins and be sunken in the center.

The bacterium can survive in crop debris, on volunteer plants, weeds and seed. This disease spreads rapidly through seed beds and fields by sprinkler irrigation and wind-driven rains. Infection generally occurs through wounds, such as those made by insects, wind-driven sand and rain, and by high pressure spraying. Warm (24-30°C, 75-86°F) temperatures with sprinkler irrigation or heavy rains favor disease development.

The use of disease-free seed and transplants is important for the early control of bacterial spot. Copper sprays can provide moderate levels of protection. When bacterial spot is present, avoid the use of overhead irrigation. Rotation to non-host crops and controlling weeds and volunteer plants are good preventive measures. Good sanitation practices, which include cleaning equipment used in diseased fields and plowing under all plant debris immediately after harvest, can help reduce losses from this disease.