Pigeon pea

Several species of aphids have been reported feeding on pigeon pea. The black legume aphid (Aphis craccivora) is the most common.

Adults feed on the flowers and reduce the number of pods that are set. In location where pigeon pea is grown over large areas blister beetles cause little damage. However, in small pigeon pea plots that are in the flowering stage during the period of peak adult activity, most of the flowers may be eaten by the beetles and crop losses maybe substantial. The adults are medium to large sized beetles (2 to 5 cm in length), usually black and yellow or black and red in colour. The immature stages (larvae) do not feed on plants. They live in the soil and eat grasshopper eggs, and are therefore beneficial.

Pod sucking bugs are primary pests of pigeon peas.

The most common pod-sucking bugs are: giant coreid bugs (Anoplocnemis spp), spiny brown bugs (Clavigralla spp), Riptortus bugs (Riptortus spp) and green stink bugs (Nezara viridula).

These bugs suck developing seeds through the pod wall. The seeds become shrivelled with dark patches. Attacked seeds do not germinate and are not acceptable as food. Fungal spores are sometimes transmitted with the mouthparts during feeding, resulting in rotting of the seeds. The spiny brown bug Clavigralla tomentosicollis is one of the most important pests of pigeon peas in Eastern Africa.

Sucking bug adults are difficult to control since they are very mobile and can invade crops from neighbouring sites.

Small circular necrotic spots (lesions) usually appear on older leaves. These spots join up causing leaf blight and leaf drop. The African isolates of the fungus produce concentric areas on the leaf spots. The disease causes severe losses when defoliation occurs before flowering and podding. The disease usually appears when plants are flowering and podding. The fungus is seed-borne. It is favoured by cool temperatures (25 degC) and humid rainy weather. The disease is more common in the long-duration and perennial varieties in Eastern Africa.

They are the most common and widespread insect pests in storage. Adults are 2-3.5 mm long. They attack both pods in the field and seeds in storage. They attack nearly mature and dried pods. Infested stored seeds can be recognised by the round exit holes and the white eggs on the seed surface. Post-harvest losses are highly variable, but losses can be over 90%.

Cutworms cut the stem of plants below the soil surface. The damaged plant wilts and withers. First instars are 0.7-1 cm, later instars are 3.5-5 cm long.

It is a fungal disease. Symptoms include partial or total wilting of plants at flowering and podding, a purple band of stems extending from the base upwards, browning of the stem tissue in the purple band area, and browning or blackening of internal tissue when the main stem or primary branches are split. Infected young plants may not show the purple band symptom but have conspicuous internal browning and blackening. Affected fields show patches of dead plants. F. udum is seed and soil-borne. The fungus survives on infected crop debris in the soil for about 3 years.

Crop rotation is advisable against diseases such as Fusarium wilt. Pigeon pea is generally grown in inter- and mixed-cropping systems in rotation with other crops, particularly cereals. However, since the fungus-causing agent of wilt of pigeon pea survives on deep-seated roots of the host, the success of rotation will depend upon the field sanitation (removal of affected plants with their roots). A 4-5-year rotation has been found to free the field completely of the wilt pathogen (causing fungal agent). However, in smallholder scenarios this is not practical due to land restriction. One-year breaks with either sorghum or fallow reduced wilt in the following pigeon pea crop from more than 50 to below 20%.

Pigeon pea rotation with tobacco has been recommended as a possible means of control because of the adverse effect of tobacco root exudates on the pathogen. For more information on  Fusarium wilt click here.

Jassids (leafhoppers) have been reported to cause damage to pigeon peas in Kenya. These small (2.5 mm) green and very mobile insects occur on the upper and lower leaf surface. The adults fly or hop away when disturbed. Nymphs resemble adults, but have no wings, and run sideways when disturbed. The eggs are inserted in the veins on the underside of leaflets. Adults and nymphs feed by sucking on the leaflets. Attacked leaves become cup shaped and yellow at the edges. Heavy attacks result in the leaflets turning red-brown, with subsequent defoliation and stunting.

Initial symptoms on stems and branches are spindle-shaped spots with light grey centres surrounded by brown margins. The centres of the spots have scattered dots (pycnidial bodies - fungal spores). The spots may join up and cause the branches or whole plants to dry up and die. Diseased plants suddenly wilt. When diseased plants are uprooted their roots are rotten and shredded. The fungus mainly attacks secondary finer roots. These roots have dark, blackened streaks underneath their barks with dots (pycnidial bodies - fungal spores). The disease could be a serious problem in late-sown and in perennial or rationed pigeon peas. Disease development is favoured by hot dry weather (30⁰C). Crops are more susceptible to the disease in the reproductive than in the vegetative stage.

The disease causes sudden death of seedlings. Infected leaves have water-soaked spots that turn brown to black. Infected leaves lose turgidity and finally become desiccated. On stems and leaf petioles the spots are slightly sunken. Affected stems or branches are girdled and foliage above dries up. Plants that are attacked but not killed often form large galls on their stems especially at the edges of spots. Thefungus does not infect the root system. The fungus is soil-borne and it also survives on infected crop debris. The disease is favoured by cool temperatures around 25 degC, cloudy humid weather and rain. Plants develop tolerance to the disease with age.

The African bollworm (Helicoverpa armigera), the legume pod borer (Maruca vitrata = testulalis) the lima bean pod borer (Etiella zinckenella) are major pests of pigeon peas in East Africa. They feed on leaves, flowers and pods, destroying them.

The African bollworm (Helicoverpa armigera)

Caterpillars are 1.5 to 4 cm long. They bore holes on pods and feed on the seeds. Usually developing in the pods and feeding partly mature seeds.

For more information on the African bollworm click here.

The legume pod borer (Maruca vitrata)

The adult of the legume pod borer is a moth with a wing span of 15-30 mm. It has light-brown forewings with white markings and pearly white hindwings. Though mainly nocturnal, the moth may also be seen during the day. They lay eggs in the flowers or buds, or on the pods. Caterpillars are whitish with black head and rows of conspicuous brown to black spots on the dorsal, lateral, and ventral surfaces of each body segment. Fully-grown caterpillars measure about 15mm in length. They pupate in the soil. Caterpillars web leaves, flower buds and pods and feed inside the web. Flowers usually show little sign of damage until they wilt and drop. They typically attack pods at the point of contact between two pods, or between a pod and a leaf or stem.

The lima bean pod borer

Adults of the lima bean pod borer are brown moths with a wing span of about 20-25 mm. They lay eggs singly or in small groups on immature pods. Young caterpillars bore into the pod. They feed inside the pod reaching a length of 12 to 17 mm and are generally found in maturing and dried pods. Young caterpillars are green, turning red later. Faeces in the form of granules are found inside the damaging pods.

It is a small black fly that lays eggs through the walls of developing pods. The maggots (white in colour and about 3 mm long) feed inside the green seed. The brown barrel shaped pupa is formed inside the pod but outside the seed.

There are no obvious external symptoms of attack till the fully-grown maggot chews holes in the pod walls leaving a window through which the flies emerge after pupation in the pod. Damaged seeds are of no value. The pod fly causes most damage on pigeon pea maturing during cool weather and pigeon pea planted at altitudes higher than 500 m above sea level.

It has been regarded as a major pest of pigeon pea in East Africa. Adults are small black weevils. The larvae are creamy white. Larvae damage the green seeds in pods but the damage is usually noticed only after adults emerge cutting the way out of the pod. The beetles also chew small holes in leaflets and flowers.

The disease can infect all aerial parts: leaves, flowers and pods. Characteristic of the disease is white greyish powdery fungal growth on affected plant parts. Small chlorotic spots develop on the upper surface of leaves and the corresponding lower surface develops white greyish powdery fungal growth. With time the powdery growth covers the entire lower leaf area. Severe infection causes heavy leaf drop. The fungus develops at temperatures ranging from 20 to 35°C , but 25°C is the optimum. The fungus survives on perennial pigeon peas and volunteer plants, and on the ratoon growth of the harvested plants. Plants with thicker leaves, as most varieties in Kenya are more tolerant to the disease than those with thin succulent leaves (Indian varieties).

Affected plants are normally stunted and eventually wilt and die. The most characteristic symptom is formation of root galls (knots) and these can be seen with the naked eye. Affected roots rot.

Symptoms appear as dark brown raised spots full of brown spores (uredia) on the lower leaf surfaces. Infected leaves dry and drop off. When disease is severe, it causes extensive defoliation. The disease is favoured by rain and wind that facilitate spore release, dispersal and development.

Red spider mites are about 0.6 mm long. They feed on the lower leaf surface causing white or yellowish spots on the upper leaf surface. Heavy infestation results in partial defoliation.

Termites can be a serious problem for coconut palms, particularly for young trees in tree nurseries or trees that have just been transplanted into the field. Termites live in the soil in hills, construct tunnel from the hills to the palms and feed on all parts of young coconut palms. Damage occurs mainly during the dry season.

Many plants have a repellent or even insecticidal effect on termites and can be applied as spray directly against termites or as barrier around the trunk of coconut palms:

• Neem: seeds and leaves (extracts or cake)
• Quassia indica or Q. amara: bark and leaves
• Sandalwood: wood
• Chinaberry, persian lilac (Melia azedarach): bark, branches, leaves, extracts
• Euphorbia sp.: "In Tanzania, especially in Dar es Salaam and coast regions, farmers plant with each seedling 2 or 3 sticks of Euphorbia sp. to protect the young palms from termite attack. On nurseries the Euphorbia plants can be planted around the seedbed to prevent access of termites to the palm seedlings and young palms. When the palms have grown big the euphorbia is simply cut down. The practice is widespread and farmers are convinced that it really does keep termites off the susceptible seedlings ( Z. Seguni, MARI personal communication)".

Thrips are small (1.5 mm long), slender, brown insects with pale yellow hind wings that appear as a yellow line down the back of the body when the insect is at rest. Adult thrips have characteristic wings; the transparent wings have a fringe of hairs around the outside edge standing out in the same plane as the wing.

Several species of thrips are common on pigeon peas in Eastern Africa and are considered important pests. These thrips feed on leaves and flowers. Main damage is due to thrips feeding on flower buds and flowers. Heavy infestation can lead to shedding of buds and flowers. However, according to reports from India, pigeonpea plants produce more flowers than the plant can sustain, so many are lost naturally and it is difficult to assess thrips damage (Ikisan, 2000).

Several species of whiteflies are found on cassava in Africa. Feeding causes direct damage, which may cause considerable reduction in root yield if prolonged feeding occurs. Some whiteflies cause major damage to cassava as vectors of cassava viruses. The spiralling whitefly (Aleurodicus dispersus) was reported as a new pest of cassava in West Africa in the early 90s.

The adults and nymphs of this whitefly occur in large numbers on the lower surfaces of leaves covered with large amount of white waxy material. Females lay eggs on the lower leaf surface in spiral patterns (like fingerprints) of white material secreted by the female. This whitefly sucks sap from cassava leaves. It excretes large amounts of honeydew, which supports the growth of black sooty mould on the plant, causing premature fall of older leaves.

The tobacco whitefly (Bemisia tabaci) transmits the African cassava mosaic virus one of the most important factors limiting production in Africa. The adults and nymphs of the tobacco whitefly occur on the lower surface of young leaves. They are not covered with white material. The nymphs appear as pale yellow oval specks to the naked eye.