Tomato

Cutworms (Agrotis spp)

Cutworms are the caterpillars of certain moths. They are serious pests of tomato seedlings. They cut stems of newly transplanted or emerged plants at the base. Cutworm damage is more critical after thinning or transplanting.

Aphids (Aphis gossypii, Myzus persicae)

Aphids such as cotton aphid (Aphis gossypii) and the green peach aphid (Myzus persicae) suck plant sap, which can reduce plant growth; they also secrete honeydew, on which sooty moulds growth. Sooty mould on fruits reduces their market value. These aphids may also transmit virus diseases during feeding such as the cucumber mosaic virus. In Kenya, aphids are occasionally found on tomatoes, but they are not considered an important pest.

Root-knot nematodes (Meloidogyne spp.)

Root-knot nematodes are very destructive to tomatoes. Damage is most serious on light sandy soils in furrow-irrigated crops. The nematodes cause small lumps known as root knots or galls on the roots. Heavily infected roots are severely distorted and swollen. In time the roots rot. The affected plants are either stunted or have tendency to wilt or even die in hot weather. The affected plants, in most cases, just wilt with the foliage still green - without yellowing. The nematode problem is primarily due to improper crop rotation.

Tobacco whitefly (Bemisia tabaci)

Tobacco whitefly is a serious pest of tomatoes. Whiteflies attack tomatoes from seedling to mature stage. They suck sap from the leaves, and may weaken the plants. Feeding of whiteflies cause yellowing of infested leaves. Immature stages (nymphs) produce honeydew on which sooty mould grows. Heavy honeydew or mould coating reduces plant growth and fruit quality.

The main damage caused by whiteflies is indirect as vectors of virus diseases. Bemisia tabaci transmits several virus diseases in tomato. In particular it is an efficient vector of the Tomato Yellow Leaf Curl Virus (TYLCV), a major disease in Kenya.

Small numbers of whiteflies do not cause major direct plant damage. However, even small numbers of whiteflies may need to be controlled in areas where TYLCV is common.

Thrips (Thrips tabaci, Frankliniella occidentalis, F. schultzeii and Ceratothripoides brunneus)

Thrips may also be a problem in tomatoes in Kenya. Thrips are small (about 1 to 2 mm long). They usually feed on the lower surface of leaves puncturing them and suck the exuding sap. They also attack buds, flowers and fruits. Attacked leaves have a silvery sheen and show small black spots (thrips excrements). Under heavy infestation attacked buds, and flowers usually fall off. Attacked fruits show speckling and small necrotic patches on the surface affecting fruit quality. Fruits may become deformed.

Thrips feed on tomatoes at all stages, but their feeding on seedlings is particularly damaging. Heavy infestation can reduce stands of young seedlings in hot weather. Thrips of the genus Thrips and Frankliniella are vectors of viruses such as the Tomato Spotted Wilt Virus (the most economically important virus in tomato production) and the Tomato Chlorotic Spot Virus.

Leafminers (Liriomyza spp.)

Leafmining flies make tiny punctures on the side of tomato leaves when feeding and laying eggs. These punctures may serve as entry point for disease causing organisms such as bacteria and fungi.

The most destructive stages are the immature stages (maggots). Maggots measure up to 3 mm in length. The maggots feed on leaf tissue inside the leaf leaving a wandering track in the form of irregular mines. Heavy mining of leaves may reduce photosynthesis affecting development of flowers and fruits. Heavy attack may cause leaf drop. This is particularly serious for tomato seedlings which may die due to defoliation. Defoliation of tomato plants may also expose fruits to sunburn and affect the market value. Leafminers attack a wide range of cultivated vegetables.

Fruit borers (Helicoverpa armiguera, Spodoptera littoralis)

Fruit borers such as the African bollworm (Helicoverpa armigera) and leaf-eating caterpillars such as the cotton leafworm (Spodoptera littoralis) attack the developing and mature fruit of tomato. The African bollworm, also known as the tomato fruit worm, is one of the most destructive insect pests of tomato, causing yield losses as high as 70% due to fruit boring. They usually bore into the fruit from the stem end, and feed on the inner parts of the fruits, causing extensive fruit damage and promoting decay caused by secondary infections.

They prefer green fruit. Caterpillar of the cotton leaf worm feeds on the leaves of tomato and bores into the fruit, especially those growing down the plant near to the soil. They are olive-green, dark grey or brown in colour with large, black, triangular spots on their back. The fully-grown caterpillars are 3 to 5 cm long. The eggs are laid in batches in one or more layers, usually on the underside of the leaves and covered with hairs. Both caterpillars have many natural enemies such as predatory ants, spiders, damsel and robber flies, and parasitic wasps and flies

Spider mites (Tetranychus spp.)

Spider mites are important pests of tomatoes. They are more prevalent in dry areas. Infested leaves show a white to yellow speckling and then turn pale or bronzed. High spider mite infestation causes defoliation, which leads to production of smaller fruits with lower content of ascorbic acid (vitamin C). Spider mite feeding on fruits causes speckling of the fruits.

The tobacco spider mite Tetranychus evansi, is one of the most damaging spider mites on tomato. This spider mite can kill plants very rapidly under hot and dry conditions. Plants with high numbers of this mite can be covered with webbing and an orange cloud of mites.

Tomato mirid bug (Nesidiocoris tenuis)

It is slender, greenish in colour with a dark brown tint on the forewings. Eggs are laid singly on the growing points, petioles and stems of the tomato plant. The young bugs (nymphs) resemble the adults, but initially have no wings. Older nymphs have wing pads. The tomato bug feed on stems, leaves and flowers of tomatoes, but prefer young leaves and growing points. Sucking by nymphs and adults results in the formation of brownish rings on stems, petioles, growing points and leaf veins, which become brittle. Repeated feeding by the bugs cause crinkling (rolling, puckering and unevenness) of leaves.

Attacked stem bases become swollen with narrow brownish rings at the apices of the swollen areas. Shedding of flowers may be partly due to feeding by this bug. Other major crops attacked include eggplant, sesame and bottle gourds. The tomato bug also exhibits predatory habits, and has been reported preying on other insect pests, such as aphids, jassids (leafhoppers), caterpillars and whiteflies. It has been identified as an important predator of eggs and young caterpillars of the African bollworm and a potential control agent of whiteflies in Europe. This bug was found frequently and in large numbers on tomatoes, throughout NE and NW Somalia (Seif et al. 2003). It has also been reported as a tomato pest in Ghana (Youdeowei, 2002). In Kenya, large numbers of this bug have been observed in tomato fields under heavy and frequent spraying of synthetic pyrethroids.

Tomato russet mite (Aculops lycopersici)

They are very tiny, approximately 0.2 mm long, and cannot be seen with the naked eye. They are yellowish, brown or pink. They have a ringed conical body with the head and two pairs of legs at the large end. They complete the lifecycle in 1 week; this explains the rapid increase of this mite in tomato fields. They prefer high temperatures and low humidity. They feed on all above-ground parts of the tomato plant, causing spotting, twisting or folding of leaves and fine cracks on the fruits. Attacked leaves and stems develop a greasy appearance and turn bronzed. The plants can drop their leaves, especially in hot weather. Fruits are then exposed to sunburn. Damage to the plant typically begins near the ground and spreads upwards. Damage can develop very rapidly, and the mites can kill plants in a few days in dry hot weather. Since the mite cannot be seen, the symptoms are easily confused with diseases. The small size of the mites makes monitoring difficult. The first signs of mite presence are the curling and bronzing of the lower leaves of the stem.

Cabbage looper (Trichoplusia ni)

In addition to the cotton leaf worm (see fruit borers), other caterpillars such as the cabbage looper (Trichoplusia ni) feed on tomato leaves. However, generally they are not of economic importance.

The cabbage looper is a green caterpillar with faint white stripes along the body. Caterpillars are about 3.5 to 4 cm long when fully-grown. As they move, they arch their back in a looping fashion, hence the common name looper. Larvae (caterpillars) chew holes in the leaves, and larger caterpillars consume great amounts of plant material.

The adult is a moth, about 2.5 cm in length and mottled, greyish-brown.

Tuta absoluta (tomato leaf miner)

Tuta absoluta is a new insect pest of tomato plant in sub Saharan Africa. The moth pest originated from Peru and has spread to Europe, Africa and Asia. In Africa, T. absoluta was detected in Tunisia (2009), Ethiopia (2012), Senegal (2013), Sudan (2010) , Tanzania and Kenya (2014) and in Uganda (2015). Although tomato plant is the main host for T. absoluta, the pest also attacks other plants in the Solanacea family including potato, nightshade, eggplant, pepino, tobacco and solanaceous weeds such as Datura.

The life cycle of T. absoluta is completed within 30-35 days. T. absoluta can have 10-12 generations per year. Females can lay up  250-300 eggs on host plants. Eggs are small, cylindrical, creamy-white to yellow and approximately 0.35 mm long. Eggs hatch in 4-6 days after egg laying. The larva is cream-colored with a characteristic dark head. T. absoluta has four larval instars. Pupation may take place in the soil, on the leaf surface or within mines. The adults are small moths with 5-7 mm body length. The adults have thread-like antennae and forewings with grey scales and black spots.

The larvae feed between the leaf layers causing irregular mines. They eventually tunnel into the stems or burrow into the fruits, leaving black frass as it tunnels.

T. absoluta is a very challenging pest to control because of its fast reproductive rate (10 -12 generations per year), short life cycle, nocturnal adults, and concealed larval stage inside the plant parts. It can cause up to 100% loss of tomato fruits if left uncontrolled.