Someone told me that their garden had bacterial leaf spot because of all the spring rains we have had this year. She is probably right on the diagnosis and right on the cause of the problem. Excess moisture on the plant leaves is the number one reason for bacterial leaf spot. Unfortunately there is no cure for the leaf spot, only prevention and control methods. Let’s talk about a couple of these today.
The first method of prevention is to plan ahead. When planting a garden or even any plant for that matter, make sure and plant it is the type of sunlight it prefers. If it is a sun plant, put it in the sun. This helps the plant dry out faster and prevent the bacteria from developing. Another way to plan ahead is to pick varieties that are leaf spot resistant. This could take some time and effort on your part, but could be very worth it in the end.
The next step in preventing the spread of the disease is to rake up any fallen leaves or fruit under the plant. The bacteria spores germinate and spread by the wind and whenever anything bumps them to send them into the air. Because the cause of the disease is moisture, pay closer attention to how close the plants are to each other and prune aggressively to keep good air circulation around the plants. Prior preparation during planting helps this technique dramatically. While pruning, use a 1 part bleach to 4 part water mixture and disinfect your cutter after every cut to prevent the spread of the disease. Don’t handle the clippings any more than you have to because the spores bounce off very easily. Bag up the clippings and throw them away. Do not burn or compost them.
It can be critical that you spread a thick layer of mulch over the ground to prevent the spores from releasing from the ground. The mulch will also help keep the ground moist and cut down on some watering. When watering, do not water overhead. That puts more moisture on the leaves and helps the spread of the disease. Water on the ground only.
There are several copper based fungicides on the market that can help suppress the effects of the disease. None of them will completely eliminate it, or completely prevent it. There is no real good organic control, but something like neem oil will help control the spreading of disease. Early prevention and careful protection is the best way to control Bacterial Leaf Spot