Why Are Yellow & Red Peppers Getting Black Spots?

Bacteria

• Bacterial spot tends to affect bell peppers when there is a lot of rain and when the temperatures are high. Spots appear on both the fruit and the leaves. On the fruit, the spots start out a light green color, then turn brown or black. The spots on the fruit are usually not larger than 1/4 inch in diameter and have a rough texture. The disease is caused by the bacteria Xanthomonas campestris pv. vesicatoria. Pepper plants suffering from bacterial spot won't produce a lot of fruit.

Blossom End Rot

• A condition called blossom end rot also causes black spots to form on the fruit of bell pepper plants. Blossom end rot looks different than bacterial spot and is not caused by a pathogen. The spots are initially light tan in color, but can become black as they are infected with an Alternaria fungus. Peppers suffering from blossom end rot are not getting enough calcium from the soil to support the formation of the fruit's cells. A plant might not get enough calcium because of drought or inconsistent watering.

What to Do

• If a pepper plant has signs of blossom end rot, cut off any fruits with the spots. A soil test allows you to see if the soil is deficient in calcium or if the rot is due to insufficient watering. Avoid using a fertilizer that is very high in nitrogen, as too much nitrogen also contributes to blossom end rot, as it prevents the plant from absorbing calcium. If a plant shows signs of bacterial spot, pull it up and discard it to prevent it from spreading to other plants.

Prevention

• When it comes to bacterial spot, your best option for control of the disease is prevention. Choose seeds or transplants that are certified disease-free or soak seeds in hot water to kill off any bacteria. Only plant peppers in the same location every three years or so to reduce the spread of the disease. Watering and fertilizing also play an important role in preventing both blossom end rot and bacterial spot. Do not water the plants from overhead, as bacteria spreads when the leaves are wet. To prevent blossom end rot, do not let the soil dry out between waterings. Peppers typically need an inch of water weekly. Add a 3-inch layer of mulch around the plants to keep the soil moist. Plants that do not receive enough nutrients from the soil are more likely to suffer from disease. Over-fertilizing with nitrogen also puts a plant at greater risk for disease.