The American Phytopathological Society lists over 35 different diseases that have been found in the U.S. However, there are about 16 that have been reported in Louisiana. Most of these you will not encounter in your home garden but knowing what’s possible and recognizing early symptoms may help to prevent total crop loss. Following is the description and recommendations for management of the most common pepper diseases in Louisiana. Cercospora leaf spot (Frogeye leaf spot) Cercospora capsici. The disease is favored by hot days (90°F) and warm nights (70°F). Lesions ¼” to ½” form on all parts of the plant but are most noticeable on the leaves. Lesions have a light brown to white interior and a brown to purple border. As the lesions grow, concentric rings may appear and the center becomes brittle and cracks. The pathogen can overwinter in plant debris. Control: The disease is usually minor and may not warrant control. Resistance has been noted in some varieties. Fungicides containing copper or chlorothalonil have been shown to be effective.

Anthracnose Colletotrichum spp. Fruit lesions usually develop during ripening but may form on fruit at any stage and later on leaves and stems. Lesions are circular with a concentric ring appearance and may become as large as 1” or more. As lesions mature, dark dots of sporangia may become noticeable. The fungus may overwinter in plant debris. Control: Use certified disease-free seed. Avoid overhead irrigation. Copper-based fungicides and those containing chlorothalonil are recommended for management in the home garden.

Figure 1: Pepper fruit with Anthracnose. APS photo.

Bacterial spot Xanthomonas euvesicatoria. Symptoms develop on leaves, stems and fruit of sweet pepper and are less severe in hot pepper. Symptoms first appear on leaf undersurfaces as small, irregular, watersoaked areas. Later, lesions enlarge, turn darkbrown to black with a pale tan center and may develop a thin, yellow halo. Generally, lesions on upper leaf surfaces are slightly sunken, and those on lower leaf surfaces are slightly raised. Leaves that are severely infected often turn chlorotic and appear ragged. Defoliation occurs under heavy disease pressure. Stem lesions appear as narrow, light-brown, longitudinally raised cankers. Fruit spots begin as water-soaked areas that later turn necrotic. These spots are rough in appearance and crack as they develop. Xanthomonas is seed-borne on the seed surface and within the seed. Infected seed and transplants moved over long distances can be the initial source of inoculum for epidemics. The bacterium also survives in crop debris, volunteer plants and in solanaceous weeds. High relative humidity and heavy dew formation on leaves, together with warm weather, favor infection and development of Bacterial Spot. The bacterium is readily water-splashed from infected transplants or debris to healthy plants. Fruit are infected through growth cracks, abrasions, insect punctures and other wounds. Control: Using disease-free seed, disease-free transplants, crop rotation and resistant varieties are effective cultural practices. Use of copper-based pesticides may be used as prophylactics.

Figure 2: Frogeye leaf spot. APS photo.

Damping-off Pythium spp.; Rhizoctonia spp.; Phytophthora spp.; Fusarium spp. This disease affects seeds, seedlings, and young transplants. Symptoms appear as brown, soft, water-soaked lesions around the soil line. Infected stems appear constricted. Infected seedlings fall over and die. Control: Use of certified disease-free seed and sterile germinating mix are cultural control measures. Captan and Ridomil can be used as a soil treatments.

Figure 3: Bacterial spot lesions on pepper leaf. APS photo.

Figure 4: Seedlings with damping off lesions. APS Photo.

Powdery mildew Oidiopsis sicula. The most noticeable symptom is a white, powdery growth on the leaf underside. The upper leaf surface may show light green to pale yellow lesions. The entire leaf eventually turns yellow or brown. Infected leaves may drop which can lead to sunburn on the fruit. Control: Sanitation and removal of plant debris are good cultural practices. Many sweet peppers show a high degree of tolerance to powdery mildew, whereas hot pepper varieties have very little resistance. Fungicides containing copper, chlorothalonil, or myclobutanil have been shown to help manage powdery mildew.

Southern blight Sclerotium rolfsii. Southern blight is a common and destructive disease with a host range of over 500 plant species. The pathogen attacks the pepper stem near the soil line causing the plant to become chlorotic and die. Brown lesions appear on the stem both above and below the soil line. Often, a white mycelial mat is evident on the stem and soil. The pathogen forms sclerotia which are dense hyphal structures about the size of a broccoli seed and are light tan to brown. These are survival structures that can survive in soil for years. Control: Growing in soil that is free of the disease, removing and destroying infected plants, crop rotation, avoiding wet soils, and soil solarization are cultural practices that will help to reduce disease incidence. Biological control pesticides containing Bacillus amyloliquefaciens have been shown to exhibit some control.

Figure 5: Pepper stems demonstrating Southern Blight infection. University of Georgia Photo.

Phytophthora blight Phytophthora caspsici. The pathogen has a wide host range and causes root and crown rot of peppers, causes black stem lesions, and can cause greyish-brown circular leaf lesions. The pathogen can also infect fruit leading to lesions typically covered with white sporangia. Infected plants soon wilt and die. Control: Field sanitation, crop rotation, and soil moisture management are recommended cultural practices. The pathogen persists in soil for years. Infection is favored by high soil moisture. Monterey Garden-Phos systemic fungicide is labelled for use to control Phytophthora in peppers.

Figure 6: Phytophthora infections on stem, roots, and leaves. APS Photo

Viruses: Alfalfa mosaic virus (AMV); Cucumber mosaic virus (CMV); Pepper mild mottle virus (PMMoV); Pepper mottle virus (PeMoV); Potato virus Y (PVY); Tobacco etch virus (TEV); Tobacco mosaic virus (TMV); Tomato spotted wilt virus (TSWV). Transmission: AMV, CMV, PeMoV, PVY, TEV are aphid transmitted. PMMoV, TMV are seed and mechanical transmitted. TSWV is thrips transmitted. AMV causes bright yellow or white mosaic blotches. There are few resistant varieties and controlling vectors is not effective. Using disease free seed and transplants is the best control. Aphid insecticides are not effective. CMV symptoms vary by virus strain and pepper variety. Stunting and distortion, necrotic specks and spots, and necrotic lines are just some of the symptoms. Some resistant varieties have been developed. Aphid insecticides are not effective. Reflective mulches to repel aphids and weed elimination have shown some effect. PMMoV causes mild symptoms on leaves but severe fruit symptoms. Fruit may be small, deformed, mottled, or have sunken or raised off-color lesions and necrotic lesions. Use of resistant varieties and certified disease-free seed are the most effective controls. PeMoV may cause small, mottled leaves on infected plants. Some strains cause systemic necrosis and apical death. Use of resistant varieties and disease-free transplants along with eliminating alternate weed hosts is the recommended management. Aphid insecticides are not effective for virus control. PVY most common symptoms are systemic vein clearing developing into dark green veinbanding or mosaic. Prevention of infection through resistant cultivars and sanitation are the main control measures. Roguing infected plants is recommended. Aphid insecticides are not effective for virus control. TEV symptoms include mosaic patterns (leaves and fruit), leaf distortion, and stunting. Use of resistant cultivars is the most effective control approach. Aphid insecticides are not effective for virus control. TMV chlorotic mosaic patterns and leaf distortion are the most common symptoms. Sanitation practices, disease-free seed, and resistant varieties are the most common control measures. TSWV symptoms may vary depending on plant variety and growth stage at time of infection. Plant stunting; chlorotic/necrotic flecking, necrotic rings on leaves, stems, and fruit; and flower and leaf drop are some of the more common symptoms. Use of resistant varieties and virus-free plants are the most effective current control measures. Controlling thrips to prevent infection is not very effective. Pepper disease incidence and severity are affected by pepper species, pepper variety, weather conditions, field conditions, and sanitation and cultural practices. These are some of the diseases you may encounter when growing peppers but using disease free seeds and transplants and following good cultural practices will generally lead to a successful pepper harvest. ~ Dr. Joe Willis

Figure 7: Virus diseases of pepper – A: Alfalfa Mosaic; B: Cucumber Mosaic; C: Pepper Mild Mottle Virus; D: Pepper Mottle Virus; E: Potato Virus Y; F: Tobacco Etch Virus; G: Tobacco Mosaic Virus; H: Tomato Spotted Wilt Virus. APS Photos

Resources:

Pernezny, K, P.D. Roberts, J.F. Murphy, N.P. Goldberg. 2003. Compendium of Pepper Diseases. American Phytopathological Society. Vallad, G. and P.D. Roberts. 2024. Some Common Diseases of Pepper in Florida. UF-IFAS. CIR946/ VH054: Some Common Diseases of Pepper in Florida