Bell peppers (Capsicum annuum) thrive in U.S. Department of Agriculture Plant Hardiness zones 8 through 11. Most varieties begin producing a harvest of peppers about 70 days after sowing, so you can quickly reap the benefits of your labor. Though bell peppers are relatively hardy, various diseases and viruses can attack the plant and require immediate treatment to prevent fruit loss and plant death.
The Phytophthora capsici fungus can appear on a bell pepper's fruit and stems during warm, humid weather periods or if the plant is given too much water. Symptoms include a thin layer of mold-like growth. The fungus can be controlled and will often self-correct itself when the conditions that prompted its appearance dissipate. Gardeners should reduce watering as much as possible, and trim back surrounding shrubs or trees to increase sunlight and airflow onto the bell pepper plant. A mefenoxam or copper spray can also be applied to kill the fungus.
Tomato Spotted Wilt Virus
Thrips, a tiny insect pest, carry the tomato spotted wilt virus and can infect your bell pepper plant with it. Signs of the virus include mottled foliage and stunted plant growth, as well as bell pepper fruit with dark black streaks. Standard insect control against thrips using products like insecticidal soap can keep this virus at bay. Bell pepper plants that become infected should be removed immediately to keep the virus from being transmitted to the surrounding plants.
Cercospora Leaf Spot
Leaf spot is relatively common, especially in gardens that don't rotate crops and have been growing bell peppers for several consecutive seasons. Signs of the fungal disease include circular spots on the bell pepper plant's stems and leaves. Without treatment, the plant will turn yellow, wilt and die. A standard vegetable fungicide will control leaf spot.
Bacterial Leaf Spot
Bacterial leaf spot is caused by the Xanthomonas vesicatoria and appears on both the fruit and foliage of infected pepper plants. The spots appear on the underside of leaves or as small blisters on the fruit's skin. The bacteria is most often introduced to a garden with a new pepper plant. Gardeners should inspect all plants carefully before planting them. Treatment options include sprays formulated with streptomycin sulfate or fixed copper, which kill the disease upon contact.