Why Do My Peppers Have Irregular Brown Spots on Their Leaves?

Bacterial Spot

• If the irregularly shaped brown spots on the pepper plant's leaves appear watery, the problem may be bacterial spot, caused by the bacterium Xanthomonas campestris pv. vesicatoria. The infection can cause the leaves to become deformed and the margins necrotic. Leaves drop prematurely, causing secondary infections, rotted fruit and sunscald. Buy only certified disease-free seed, look for resistant varieties and make sure the plants have good drainage, as the bacteria can spread through splashing water. Apply a solution of copper/macozeb once a week as soon as you notice the infection. If you start pepper plants indoors, apply streptomycin when the first true leaves appear and continue until the plants are set out in the garden. Follow package instructions carefully. Clear away all weeds and plant debris and dispose of it away from the garden. Sanitize gardening tools between uses and between plants to avoid spreading the disease.

Leaf Scorch

• If the leaves develop brown spots between the veins, leaf scorch may be to blame. Scorch usually follows long, dry periods, often with high winds and blistering sunlight. The plant transpires, or sweats, moisture faster than the roots can supply more. The leaves may fall off prematurely in severe cases. Provide extra water during droughts and water thoroughly. Fertilize the plants regularly and mulch around the base of the plant to keep the roots cool and preserve moisture. If the pepper plant is at the mercy of too much sunlight, erect a screen to filter the light.

Phytophthora Blight

• Phytophthora capsici causes blight and may add root rot and damping off to its list of damages if left uncontrolled. Leaves develop small, dark green spots that fade out and appear scaled. The roots may develop cankers and the entire plant may suddenly wilt. The fungus is found in the soil and can infect the pepper at any time, or it can travel on the wind. Rotate vegetable crops annually and make sure the garden is well drained. A raised bed provides the best drainage. Use a fungicide formulated to control phytophthora capsici and follow label directions for proper application. Avoid overhead watering, as the spores can travel in water.

Cercospora Leaf Spot

• Cercospora capsici causes almost identical symptoms to bacterial leaf spot and has the same remedies. Cercospora capsici and Alternaria sp., a secondary infection, are often found together. Take the infected leaves to your cooperative extension service office to determine which of the diseases is attacking your pepper plants. Cercospora must have moisture to germinate and penetrate the plants, and heavy dew provides enough water for the infection to spread. Avoid splashing water and apply fixed copper mixed with streptomycin every week to 10 days. Do not use streptomycin on plants already in the garden. Make sure the plants have good drainage and air circulation so the leaves will dry more quickly after watering. Disinfect all garden tools between uses.