1. Anthracnose (Colletotrichum capsici)
Anthracnose caused by Colletotrichum spp. is a major problem of ripened fruits. The fungus produces dark, sunken spots up to 2.5 cm across on sweet pepper. The spots occur on green and ripe fruits and their surface may be covered in moist weather with salmon-pink mass of spores. The fungus is seed-borne
2. Bacterial wilt (Ralstonia solanacearum)
The disease occurs in scattered plants or groups of plants in the field. Characteristic symptom is wilting of the entire plant with no leaf yellowing.
The bacteria have a wide host range and can survive in the soil for long periods.
The disease is favoured by wet, warm conditions. Peppers are not as susceptible as eggplants, potatoes, tobacco or tomatoes. Rotation is not effective as the pathogen can survive for a long period - several years - in the soil and also attack a wide range of crops and solanaceous weeds.
Photo: Bacterial wilt symptoms on pepper
1.3. Fusarium wilt (Fusarium oxysporum f.sp. capsici)
Disease symptoms include drooping and yellowing of lower leaves followed by wilting of the entire plant. Leaves on infected plants remain attached and the vascular system of the plant is discolored, particularly in the lower stem and roots.
Photo. Chilli field infected with Fusarium wilt.
The fungus lives indefinitely in the soil and is spread in irrigation water. It is very susceptible to changes in temperature and soil moisture. The optimum temperature for disease development is 24 to 27° C. Soil moisture has the greatest influence. The wilt does not occur in dry soil, but it is serious in poorly drained fields.
4. Powdery mildew (Leveillula taurica)
Yellowish blotches or spots appear on the upper leaf surface. The leaf surface is covered with a white to grey powdery fungal growth. The disease progresses from the older to younger leaves and shedding of the foliage is pronounced. Leaf defoliation leads to reduction in size and number of fruits. It also results in fruits being sun-burned. The disease is favoured by warm, humid and dry weather. The fungus causing powdery mildew also attacks eggplants and tomatoes. Overhead irrigation reduces disease severity.
5. Viral diseases
About 17 viruses have been reported to attack peppers. Those considered economically important in Africa include alfalfa mosaic, chilli veinal mottle, cucumber mosaic, pepper veinal mottle, potato Y, tobacco etch, tobacco mosaic, tomato spotted wilt and chilli leaf curl. Most of these viruses are transmitted by insects, infected seed and a few by mechanical means and infected seed: the first six above listed viruses are spread by aphids; tobacco mosaic is mechanically transmitted and infected seed; tomato spotted wilt by thrips; and chilli leaf curl by whiteflies.
General symptoms include mosaic patterns on leaves, yellowing , ring spots, leaf deformation or distortion, curling of leaves, and/or stunting of plants. They may also cause reduction of fruit size, distortion, and/or ring patterns.
Photo. Symptoms of viral diseases on pepper
Management practices often used to reduce viral disease incidence include:
Plant resistant cultivars, if available
Select planting dates to avoid high population of vectors
Close plant spacing to compensate for diseased plants
Use barrier crops to minimize virus spread
Use oil sprays to reduce virus transmission by aphids
Use reflective mulches to repel aphids and thrips.
Use certified disease-free seed in case of tobacco mosaic virus
6. Chilli Thrips (Frankliniella spp., Scirtothrips dorsalis, Thrips tabaci)
Thrips usually feed on all above ground parts of plants, preferring the underside of young leaves, flowers and fruits. Often they are concealed under the calyx. Plant damage results from thrips puncturing leaves and sucking the exuding sap. At the initial stage of infestation leaves have a silvery sheen and show small, dark spots of faecal material on the underside. When the attack increase leaves curl upward, wrinkle and finally dry up. This may cause fruit sunscald.
Heavy feeding damage turns leaves, buds and fruits bronze in colour. It may cause wilting, retardation of leaf development and distortion of young shoots resulting in stunted plants. Attack on fruits causes deformation and scarring (manifested as brown lines) of the fruits making them unmarketable, especially fruits for the export market. Thrips attack at the seedling and early stages of the crop delays crop development. Thrips transmit the tomato spotted wilt virus in peppers. S. dorsalis transmit the leaf curl disease of chillies.
Photo: Thrips damage on a chilli pod
Aphids suck the sap from the plants; they generally attack the crop in dry period and at the later stages of the crop. The quality of the produce is spoiled by imparting blackish colour to the Calyx and pods. They also act as a vector to virus.
The aphids can effectively be controlled by spraying the crop with insecticides like cypermethrin (1ml/1L of water) at 15 days interval
8. Whiteflies (Bemisia tabaci, Trialeurodes vaporariorum)
Whiteflies damage plants in three ways. Whitefly immature stages (nymphs) and adults suck sap from leaves. Their feeding, in addition to removing plant nutrients, produces chlorotic spots on infested leaves. Nymphs excrete a clear sugary liquid known as honeydew, which often completely covers the leaves during heavy infestation. Honeydew supports the growth of a black sooty mould, and as a result the leaves may turn black, affecting photosynthesis. Whiteflies are vector of important viral diseases such as chilli leaf curl, tiger disease, Serrano golden mosaic, and Texas pepper geminivirus.
9. Blossom End Rot (Physiological disorder)
The end of the fruit becomes off-whitish to brown in colour and takes on a “sunken in” appearance. As the fruit matures, these symptoms become more pronounced and the colour of the rot becomes dark brown to almost black.
Photo: Blossom end rot on Capsicum fruits
Boost the soil with calcium by adding lime, dolomite, gypsum or composted animal manures before planting the seedlings.
Water regularly: Capsicum continue to flower and bear fruit for prolonged periods of time, so ensure the soil around their roots is kept moist
Avoid fertilizers with a high nitrogen content: Nitrogen fertilizers will promote leaf growth at the expense of fruit, allocating calcium to the leaves instead of to the fruit.