Peppers

Moths of fruitborers are active at dusk and at night, feeding on nectar and laying eggs on leaves. Caterpillars feed on leaves, flowers and fruits. Although severe leaf damage by feeding of African bollworm (Helicoverpa spp.) caterpillars may slow plant growth due to reduced leaf area, caterpillar feeding on leaves is usually of not economic importance. The bollworms are about 2-3.5 cm long.

The main damage occurs on flowers and fruits. Attack on flower buds results in flower abortion. Caterpillars usually bore holes in fruits, causing extensive damage and promoting decay from secondary infection by diseases.

African armyworm (Spodoptera spp.) species are basically leaf-eaters and may cause defoliation when present in large numbers. They also feed on fruits, rendering them unmarketable.

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.

Aphids (cotton aphid and green peach aphid) occur in colonies initially around tender plant parts (growing points, young stems and leaves, flower buds) and on the lower leaf surface. When numerous they can be found on all above ground parts of the plant. Aphids damage plants in three ways: by sucking their sap, excreting a sticky substance (honeydew) that coats the plants, or/and by transmitting viral diseases.

Feeding by aphids causes distortion (curling, wrinkling or cupping) of young leaves, chlorotic spotting and mottling of older leaves, and may lead to stunting and wilting of plants. Growth of sooty mould on honeydew excreted by aphids reduces photosynthesis and affects fruit quality.

Aphids cause indirect damage as vectors of important viruses such as alfalfa mosaic, chilli veinal mottle, cucumber mosaic, pepper mottle, pepper severe mosaic, pepper veinal mottle, potato Y and tobacco etch virus.

Soft rot often begins in the peduncle and calyx tissues of harvested fruit. Infection can occur through wounds anywhere on the fruit. Fruit infected on the plant collapses and hangs on the plant like a water-filled bag. When the contents leak out, a dry shell of the fruit remains.

The bacteria are soil-borne. Soft rot is primarily a post-harvest problem although it can occur in the field being facilitated by injuries to the fruit by insects and water splash. The disease is serious during rainy periods because the bacteria are splashed from the soil onto the fruit, which are more susceptible due to their high moisture content.

Leaves, fruit and stems can be attacked by the disease. Leaf spots begin as circular, water-soaked that become necrotic with brown centres surrounded by yellowish borders. The spots are sunken on the upper leaf surface and slightly raised on the lower surface. On stems spots are elongated. Affected leaves turn yellow and drop. Affected fruits have raised brown spots that are wart-like in appearance. The disease has a wide distribution wherever peppers are grown. It spreads rapidly during warm, rainy conditions. High relative humidity with free moisture on leaves for long periods favours infection. Ideal temperatures for infection are above 20°C . The bacterium is seed-borne and survives in crop debris.

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. Cross sections cut from roots and lower stems of diseased plants exude milky streams of bacteria from the vascular system when suspended in water. 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.

Broad mites are tiny (0.1-0.2 mm long) and cannot be seen with the naked eye, and are even difficult to detect with a hand lens. An attack by the broad mites can be detected by the symptoms of damage. They live on the underside of leaves, tender stems, fruits, flower peduncles and flowers. Their feeding produces discolouration, necrosis of tissues and deformation. Initial attack occurs on the stems of terminal shoots and the lower surface of young leaves.

Young leaves turn narrow, twisted or crumpled, fail to elongate and finally may wilt and dry, giving the plant a scorched appearance. Older leaves are generally cupped with corky brown areas between the main veins on the lower side of the leaves. The succulent part of the stem of young plants may become slightly swollen, roughened or russeted. The foliage becomes rigid. Attacked fruits become deformed with a cork-like surface or fail to develop. Severely infested fruits fall, and yield is significantly reduced. Symptoms remain for a long period of time after control.

Spots on leaves are brown and circular with small to large light grey centres and dark brown margins. Spots on stems, petioles and peduncles are typically elliptical and also have light grey centres with dark borders. Infected leaves are shed. Extensive defoliation occurs under severe disease pressure. Fruits are not attacked. The fungus survives on seeds and in crop debris. The disease is favoured by prolonged periods of wetness.

It is a common and destructive disease of peppers widespread in the tropics. The fungus attacks the stem at ground level eventually girdling and killing it. White fungal growth usually is visible on the base of the stem and on the soil line around the base of the plant. On the white fungal mat, sclerotia (resting fungal spores) about the size of mustard seed that are tan to brown when mature are produced. High soil moisture and temperatures (30-35°C ) favour disease development. Symptoms are more severe during dry conditions following a wet period. The fungus has an extremely broad host range and it is also a good saprophyte.

Cutworms are the caterpillars of various moths, belonging mostly to the genus Agrotis. Young caterpillars feed on leaves making small holes. After few days they drop to the soil where they live until pupation. Caterpillars remain in the soil during the daytime coming out at night to feed. They cut stems of young seedlings at the level of the soil, killing them and affecting establishment of the crop. Some Spodoptera species, in particular S. littoralis act sometimes as cutworms.

Caterpillars, in particular under hot conditions, hide during the day in the soil around the base of the plants, and may cut them, especially seedlings, at the base of the stem. At night they climb into plants to feed.

Seedlings fail to emerge (pre-emergence damping-off); small seedlings collapse (post-emergence damping-off); seedlings are stunted through root rot and / or collar rot. Nursery beds show irregular patches. The fungi causing seedling diseases are soil inhabitants. Pythium spp. are favoured by low temperatures while R. solani and Fusarium spp. thrive at higher temperatures.

Fruit fly females lay eggs under the epidermis of the fruit. After emerging from eggs maggots generally move to the core to feed, but they may also feed on the walls of the fruit. This causes secondary rot and premature fruit fall. An infested fruit usually has a small dimple where the female fly deposited an egg. As the maggot matures inside the fruit, the fruits turn red prematurely, becoming soft and rotten.

Soft spots can often be seen where the maggot has fed on the fruit. When infested fruit is picked, the cap usually separates from the fruit because the maggot has eaten the core. Fruit may drop from the plant. Maggots remain in peppers until fully grown (from 2 to 3 weeks). At this time the maggot leaves the pepper, drops to the soil to pupate. Yield losses can be considerable. One maggot can destroy an entire fruit.

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 discoloured, particularly in the lower stem and roots. 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.

Female flies make numerous small, whitish punctures on the foliage when feeding and depositing eggs. These punctures can serve as entry points for disease-causing organisms such as bacteria and fungi. The eggs hatch into tiny yellow maggots that feed on leaf tissues leaving a wandering track known as mines. Full-grown maggots come out of the mines to pupate in the soil beneath the plants or on the foliage. Maggots are the most destructive stage.

The mines may reduce photosynthetic activity, affecting development of flowers and fruits. In severe infestation, the leaves might be completely mined, dry and fall off prematurely, causing loss of vigour and turgidity of the plant. This may eventually result in wilting, in particular in warm weather, leading to yield loss, fruit sunscald, or in serious cases death of the plant, especially of young pants.

All parts of the pepper plant can be affected. Seedlings can be killed. Collar rot and wilt phase is most common and is characterised by a dark brown stem discolouration extending upward from the soil line accompanied by a sudden wilt of the entire plant. Upper stem lesions (spots) are also dark brown and occur primarily at branch points causing death of branches above the lesions. Leaf spots are round or irregularly shaped, dark green and water-soaked. They later dry and become light tan.

Fruit infection begins as water-soaked, dull green spots that expand rapidly to cover the entire fruit. Later the fruits become flaccid and wrinkled but do not detach from the affected plants. The host range of the fungus includes cucurbits, eggplants and tomatoes. The fungus can survive on and in seeds, in soil and in crop debris. The collar rot and wilt phase is most severe in over-irrigated or poorly drained fields. Aboveground infection is associated with extended periods of rainfall or overhead irrigation.

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.

Symptoms of infestation by root-knot nematodes are similar in all crops: wilting of plants and if infested plants are pulled from the soil the roots can be seen to be distorted, swollen and bearing knots (galls). The galls on pepper are much smaller than those on cucurbits or tomatoes. The infested roots eventually rot and affected plants die.

Spider mites suck the sap of the plants, causing mottling of the upper leaf surface. Infested leaves first show a white to yellowing speckling, and then eventually turn bronze and fall off as the infestation becomes heavy. Spider mites prefer the lower surface of the leaves, but in severe infestations occur on both leaf surfaces as well as on stems and fruits. High infestations cause defoliation.

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 predispose fruits to 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 transmits the leaf curl disease of chillies.

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. 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.

Viral diseases are particularly difficult to firmly diagnose by symptoms because there is so much overlap in symptomatology. Furthermore, symptom expression can be altered by many factors among which are cultivar, age of host plant, environmental conditions, host plant nutrition, and viral strains, not to mention the occurrence of virus mixtures. 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.

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.