There was an alert put out on another posting about black spots being found on pepper plants, accompanied by leaf drop. If you’re experiencing that, here’s my best guess on what’s going on.
There are two common diseases in peppers that produce black spots: Bacterial Spot and Cercospora Leaf Spot.
Bacterial spot is characterized by small, irregular black spots along the edges of the first leaves. On older plants, a small, pale green, or watersoaked, slightly raised lesion appears on the underside of the leaf. The spots are often surrounded by a yellow halo, and the centers of the spots appear dry. Some leaves may drop while still green.
The disease is widespread in tomatoes and peppers in the southeast, is usually seed-bourne, and may overwinter in infested plant debris in the soil. Contaminated seeds or seedlings are common sources of infection. Frequent warm, driving rains help the disease to develop. Once the disease develops in a few plants, it can spread rapidly to all of the plants. Splashing rain drops, overhead irrigation, or touching wet plants can spread the bacteria from diseased to healthy plants.
Once your plants are infected, it’s difficult to control. Copper sprays can be used to prevent the spread of disease, but some research studies have shown that the act of spraying can do more to spread the disease than to control it.
Learn more from the Virginia Cooperative Extension and from the College of Agriculture and Life Sciences, Plant Pathology Extension, North Carolina State University.
Cercospora Leaf Spot
Cercospora Leaf Spot is characterized by circular tan spots, with dark rings and yellow halos. Numerous spots lead to yellowing leaves. This is a fungal disease, which survives in, or on, seed. The spores can also survive in infected plant debris from season to season. It becomes most severe after warm temperatures accompanied by heavy moisture, so the frequent rains we’ve had make sense. It can also be spread plant-to-plant by splashing water.
Remove the infected plants and one or two neighboring plants that may have the disease but not yet be showing symptoms. Allow for good air circulation around plants and avoid extended periods of leaf wetness. There are protective fungicides you can apply too.
To prevent both diseases, rotate your crops every year and be sure and destroy plant debris. Don’t save the seed. If you plant from seed, use clean seed. You can find instructions online for a quick seed soak in bleach to kill disease, too.
Note to johnboat: send me a photo of your leaves (firstname.lastname@example.org) with black spot and I’ll post it here. The links above show photos, so that may help you to diagnose the problem. You can also contact the Virginia Cooperative Extension for diagnosis.