Bacterial wilt (Ralstonia solanacearum)

This disease occurs with bad drainage, especially in the hot, wet season and is often combined with symptoms of root-knot nematodes. Plants wilt and die suddenly. When newly infected stems are cut crosswise and placed in water, a greyish or yellowish ooze appears from the cut stem. The pathogen is soil-borne with a wide host range. Root-knot nematode infestation aggravates the disease development.

Powdery mildew (Leveillula taurica)

Symptoms appear as yellowish spots on the leaves. On the lower surface of affected leaves the spots are covered by a whitish growth constituting spores of the fungus. Affected leaves eventually dry up but do not fall off. The fungus is endophytic (grows within the leaf contrary to other powdery mildew fungi that are grow on surface of the leaves). It has a wide host range. It is not seed-borne but it survives on herbaceous weeds and other susceptible hosts. Temperatures slightly above 20° C, dry conditions and fairly high relative humidity favour disease infection. However, fungal dispersal takes place mainly at low humidity.

Anthracnose (Colletotrichum melongenae)

Spots of fruits are sunken. When weather is moist, the spots get tan-coloured (growth of fungal spores). There may be several spots on affected fruit and they may join up and cover the whole fruit. Severely affected fruits drop. Eventually, affected fruits dry and become black. Most often, soft-rot bacteria invade affected fruits and cause a soft watery decay. The fungus usually attacks fruits on plants that are weakened or over-ripe. Infection is favoured by relative humidity close to 100% and temperatures between 21 and 30° C.

Phytophthora fruit rot (Phytophthora parasitica)

Phytophthora fruit rot fungus can cause damping-off in seedbeds, leaf spotting and collar rot on the main stem final resulting in plant death. The fungus may attack fruit at any growth stage and any part of the fruit. Spots on the fruit are dark brown, water-soaked and may have a light-coloured border. A whitish mould develops on the spots when wet conditions prevail. The spots are neither sunken nor exhibit concentric rings (zonation). Infected fruits drop prematurely.

The fungus is soil-borne. It is spread in the field by run-off water and farm implements. The disease is favoured by prolonged periods of high moisture and temperatures near 30° C.

Late blight (Phytophthora infestans)

The late blight fungus affects tomatos, potatoes and eggplants but not pepper. Its symptoms consist of brown spots with purplish tinge and they can develop on leaves, stems, branches and both green and ripe fruits. In moist weather it can cause complete defoliation and rotting of fruits.

Fusarium wilt (Fusarium oxysporum f.sp. melongenae)

Affected plants show yellowing of leaves that progressively wilt and die from bottom upwards. Woody stem and root tissue of diseased plants turn brown. This fungus does not affect tomatoes. Optimum temperature for its growth on eggplants is 27.8° C.

Early blight or Alternaria leaf and fruit spots (Alternaria spp.)

Several Alternaria spp. are involved. These include A. melongenae, A. solani and A. tenuis. They cause leaf spotting and fruit rots. They produce leaf spots with concentric rings. The spots are mostly irregular, 4 to 8 mm in diameter and may enlarge and cover a large area of the leaf blade. Severely infected leaves drop off prematurely resulting in the reduction of yield. Fruit spots are circular, brown, dry and hard.

Cutworms (Agrotis spp.)

These caterpillars are serious pests particularly in nurseries and of newly transplanted plants. They attack eggplants and many other plants at night. They cut seedlings and usually drag them down into the soil leaving the clean-cut stem. They cannot cut older plants. Large ground beetles, frogs, and birds prey cutworm.

Budworm (Scrobipalpa blapsigona)

It is reported as one of the major pests of eggplants in Ghana. The small brown caterpillars of the budworm bore into flower buds and feed inside the flowers. This causes the flowers to drop off. Budworm damage is often overlooked, but it can be serious, leading to very low fruit set (Youdeowi, 2002).

Whiteflies (Bemisia tabaci)

Whiteflies feed on leaves of eggplant sucking plant sap. Whiteflies are vectors of the mosaic virus reported to occasionally affect eggplant in West Africa.

Root-knot nematodes (Meloidogyne spp.)

Eggplant is highly susceptible to root-knot nematodes, especially on sandy soils. 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. The infested roots eventually rot and affected plants die.

Weeds

Eggplant is slow to become established and cannot compete with aggressive weeds. Weeds also harbour insect pests and diseases.

Mole crickets (Brachytrupes spp.)

Mole crickets have been reported as major pests of eggplants in Ghana. They live in the soil, feeding on the roots of many vegetables. They cut seedlings and drag them down into the soil leaving the clean-cut stem.

Thrips (Thrips spp and Frankliniella spp.)

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.

Thrips attack eggplant mostly during the dry season. They cause browning of leaves, especially on the lower leaf surface. In severe cases, the entire leaf dries. Thrips feeding on fruits causesscarring, irregular discolouration and deformation, which reduce the market value of fruits.

Cotton leafhoppers or jassids

They are small insects (1-3 mm long), green in colour with slender tapered bodies. Leafhoppers are very mobile. The adults hop away when disturbed. Nymphs resemble adults, but have no wings, and run sideways when disturbed. The eggs are inserted in the leaf tissue on the underside of leaflets. They feed mainly on the underside of eggplant leaves, causing small yellow patches on leaves. Infested leaves curl upwards along the margin. Under heavy attack, leaves turn yellow and then brown and dry, giving a burned appearance. Fruit setting may be very low. Leafhoppers multiply rapidly during dry spells and can cause extensive damage.

Aphids (Aphis gossypii)

Aphids are found in groups on the under surface of young leaves. When numbers increase they can move to upper leaf surfaces, stems and flowers. Aphids, in particular the cotton aphid, can become important pests in the cool dry season.

Spider mites (Tetranychus spp.)

Spider mites may become serious pests of eggplant during the dry season. Attacked leaves show a stippled appearance (white specks), and their surface covered with a fine web. Continuous infestation causes the leaves to dry-up. The plants are stunted and yields reduced.

Epilachna beetles (Epilachna spp.)

The adult beetle is oval in shape, about 6 mm in length and reddish brown in colour with black spots on their backs. They look very similar to the beneficial ladybird beetles (predators), but the body of this pest ladybird beetle is covered with short, light coloured hairs, which give them a non-glossy or matt appearance. The larvae are pale yellow and covered with branched spines.
They feed on the leaves of eggplants by scraping the surface and eating the leaf tissue between the veins. Attacked leaves may be completely stripped to the mid-veins to skeletons. They may also feed on fruits causing small shallow hollows on the fruit surface. High numbers of these beetles can cause considerable damage.

Eggplant lace bug (Urentius hystricellus)

It is a small bug (about 3 mm in length), brownish in colour. Its body is covered with spines and the wings show a distinct lace-like appearance. Nymphs resemble adults, but are initially wingless, developing wings as they grow. Both adults and nymphs are usually found in groups on the underside of leaves. They suck sap from the leaves causing whitish to yellowish mottled patches on the leaves. In case of serious infestations the leaves turn entirely yellow and drop off. Attacked leaves are speckled with small black shiny spots, which are the faeces of the bugs.

Shoot and fruit borer (Leucinodes orbonalis)

It is a major pest of eggplant. The adult is a small moth, with a wingspan of 18-24 mm, white in colour with a pink and bluish tinge, and a few brown spots on its wings. Moths lay creamy white single eggs on leaf undersides, stems, flower buds, or the base of fruits. Upon hatching the caterpillars (white in colour) bore into the top section of fruits and tender shoots. Caterpillars develop inside fruits and stems reaching a length of 15-18 mm. When fully-grown, caterpillars make a small hole in the fruit or shoot and drop to the soil and pupate among fallen debris.

When plants start bearing fruits, most caterpillars prefer to feed on the tender fruits. The damage to the shoots is not seen until they droop as a result of the caterpillar feeding inside them. Recently damaged fruits are not easy to detect. The first indication of damage to the fruit is a small hole just below the calyx where the insect has entered. Fruits are filled with frass. They change colour and taste; they drop off and are unmarketable. Caterpillars are difficult to control with pesticides. Within hours of hatching from eggs, caterpillars enter the shoots or fruits, and are not reached by contact pesticides.