Bacterial Leaf Spot
Symptoms: Infected plants have brown or black water-soaked spots on the foliage, sometimes with a yellow halo, usually uniform in size. The spots enlarge and will run together under wet conditions. Under dry conditions the spots have a speckled appearance. As spots become more numerous, entire leaves may yellow, wither and drop. Members of the Prunus family (cherry, plum, almond, apricot and peach) are particularly susceptible. The fruit may appear spotted or have sunken brown areas. Bacterial leaf spot will also attack tomatoes, peppers and cabbage family crops in vegetable gardens.
Bacterial leaf spot is most active when there is plenty of moisture and warm temperatures. During the summer months, especially if plants are watered by overhead sprinklers, sufficient moisture may be present for infection when the bacteria are splashed or blown on to leaves. Wind and rain transmit the bacteria to plants.
This disease overwinters in the soil around infected plants as well as on garden debris and seeds. It will also remain in the twig cankers, leaves, stems and fruit of infected trees.
Control: Choose resistant varieties if possible. Keep the soil under the tree clean and rake up fallen fruit. Prune or stake plants to improve air circulation. Make sure to disinfect your pruning equipment (one part bleach to 4 parts water) after each cut. Use a thick layer of mulch to cover the soil after you have raked and cleaned it well. The mulch will prevent the fungus spores from splashing back up onto the leaves. Water in the early morning hours (avoiding overhead watering if possible) to give the plants time to dry out during the day. Avoid overwatering.
There is no cure for plants infected with bacterial leaf spot. Apply copper-based fungicides weekly at first sign of disease to prevent its spread. This organic fungicide will not kill leaf spot, but prevents the fungus spores from germinating. Applications of Fire Blight Spray will also control the disease. Use as a preventive treatment or apply at first sign of water soaked leaves.
Photo Credit: University of Kentucky