Bacterial Leaf Spot (bacterium – Xanthomonas campestris pv. vesicatoria): The bacterium causes spots on both foliage and fruit. Small, yellowish green to brown spots develop on the leaves. Under favorable weather conditions, spots become numerous and sometimes coalesce into large spots. Infected leaves turn yellow and fall off. The disease is seed and soilborne. Infected seed serves as source of infection to emerging seedlings. Splashing rains spread the organism from diseased to healthy plants in the field. Control can be obtained by using disease-free seed and starting a preventative fungicide program early in the growing season. Applications should be made at periodic intervals and continued during the growing season. Genetic resistance may be available in certain types of peppers, however, most of the common green pepper types are susceptible.
Black Spot (unknown, possibly physiological): There are black circular or irregular-shaped spots on mature fruit that are beneath the epidermis and are not raised. The discoloration extends to the interior of the fruit. No pathogens have been found in association with this disease and factors required for its development are not known. The disease occurs occassionally in Texas.
Damping Off (fungi – Rhizoctonia, Pythium spp.): Small, emerging seedlings wilt and die soon after emergence. Root systems of surviving plants are damaged, resulting in stunted plants and poor yield. Use high quality seed that have been treated with a fungicide and plant on a well-drained bed.
Herbicide Injury: Trifluralin (Treflan) injury can cause swelling of the stem near the soil line.
Leaf Spot (fungus – Cercospora capsici): This disease rarely occurs in Texas. Spots on leaves are large and oval or somewhat oblong, with light gray centers. Spots may also be present on the stem. Severely infected leaves turn yellow and drop. The fungus does not live in the soil but is carried in the seed. Most field infections can be traced to infected seed. The spores of the fungus can be carried by wind and splashing rains. Control can be attained by using disease-free seed that are treated with a fungicide. Fungicide applications at 7 to 10 day intervals will check the disease in the field.
Phytophthora Blight (fungus – Phytophthora capsici): The disease is caused by a fungus that lives in the soil and may be carried in seed. Infection usually takes place at the soil line; diseased plants may be girdled at the base causing sudden wilting and death of plant. Diseased parts of the stem shows a dark green, watersoaked band extending from the soil line to several inches up the stem. This band later dies and turns brown. When peppers are grown with furrow irrigation, sometimes a single infected row is observed in the field. This is the result of the fungus being carried by water down the furrow from a diseased plant and resulting in the infection and death of several plants in the same row. Planting on a raised bed and avoiding excessive moisture in the plant bed are the best means of controlling this disease.
Powdery Mildew (fungus – Leveillula taurica): Yellow areas that may become brown occur on the upper leaf surface. A white, powdery growth occurs on the underside of the leaf. Heavy infection may result in defoliation. The disease is favored by warm, humid conditions. It is not a common or significant disease in Texas.
Southern Blight (fungus – Sclerotium rolfsii): The fungus attacks the stem of the plant at or near the soil line, causing the plant to wilt and die. A white, cotton growth is observed on the surface of the stem. Later, pink to brown bodies resembling radish seed appear in the fungal growth. Crop rotation and deep plowing are means of controlling this disease. Soil fungicides may be helpful where Southern Blight has been a problem.
Sunscald (physiological): Portions of the fruit have a dried, bleached appearance and are sunken. The tissue is often colonized by saprophytic fungi, which give it a black, velvety appearance and lead to the wrong conclusion that a fungus is the cause of the problem. This disease occurs as a result of exposure of fruit to direct sunlight and can be a consequence of the defoliation caused by leaf-infecting pathogens.
Mosaic (virus): Several viruses are known to attack pepper. Often plants are infected by a combination of viruses, rather than by a single strain. Young leaves of affected plants show a greenish-yellow mottle and may be curved and irregular in shape. Leaves curl upward and under severe infection are bunched, very small and discolored. Plants are stunted and have a bunched appearance. Fruits are small, misshapen and of poor quality. Severe infection can result in the complete failure of the crop. There are no effective means of control. The virus overwinters in perennial weeds and is transmitted from weeds to healthy plants in the fields by aphids. Environmental conditions favoring aphid multiplication and migration into the field will result in severe outbreaks of the disease. Keeping fields clean of weeds around the edges and turnrows and controlling insects may help in reducing spread of the disease. Resistant varieties are now available in limited supply. Check with your county Extension agent on currently used varieties.