Nematodes (Meloidogyne spp., Pratylenchus brachyurus and Radopholus similis)

In some areas, nematodes reduce yields. Root-knot nematodes (Meloidogyne spp ) can be a problem in nurseries. Infested roots develop knots or galls. They later die and devoid of lateral roots. Affected plants show chlorosis and stunted growth.

Tea mites and spider mites

Mites are among the major pests of tea. Sporadic yield losses in the affected areas in Kenya are estimated to be about 50%. Growth of young tea is reduced by mites by about 30%.

1) The red crevice tea mite (Brevipalpus phoenicis)
They are also known as the false spider mites or the scarlet mites. They attack leaves of all ages, distorting them. They feed on the undersides of leaves, especially between the main veins at the petiole end. Corky areas are formed on the underside of leaves, especially between the main veins at the petiole end of leaves; attacked leaves may dry up and be prematurely shed; they may cause serious defoliation, resulting in reduced yield.
Numerous tiny red mites can be seen in the bark crevices of the new wood. A few bushes may be heavily attacked, leaving the majority almost free from attack. This mite is a major pest of tea, causing heavy damage especially in prolonged drought. It occurs in all growing areas in Kenya, being serious around the Mount Kenya region (Sudoi et al., 1994).

2) The tea red spider mite (Oligonychus coffeae)
It is also called red coffee mite. It may cause considerable losses to tea production. Mite attacks are usually confined to few bushes. These mites are reddish brown and purple. They feed together on the upper surfaces of the leaves, the cast skins of the immature stages remain stuck on to the leaf and maybe seen with the unaided eye as irregular white spots. The upper surface of fully hardened leaves turns yellowish brown, rusty or purple colour. If the tea bush is under drought stress, flush leaves may also be attacked. They usually prefer older leaves but in heavy infestations younger leaves maybe attacked. This mite has been recorded in all tea growing areas in Kenya in low to moderate infestations (Sudoi, 1991).
For more information on spider mites click here.

3) Yellow tea mite (Polyphagotarsonemus latus)
It is also known as broad mite. It is a minute mite yellowish to whitish in colour and cannot be seen with the naked eye. This mite is a sporadically serious pest in tea nurseries, and has been reported as a common pest of tea in Tanzania (Bohlen, 1973).
Attacked leaves remain small, are crinkled, or otherwise distorted with corky brown areas between the main veins on the underside of the leaf. The plants are severely stunted in case of serious infestations.

Cutworms (Agrotis segetum)

Caterpillars of the common cutworm occasionally attack seedlings by feeding on the roots and cutting off the stems.

Crickets

Crickets are fat, brown insects, 2 to 5 cm long. The front legs of the mole cricket are broad and curved adapted for digging. Many crickets live in burrows in the soil. Adults and nymphs of the tobacco cricket (Brachytrupes membranaceus) and the African mole cricket (Gryllotalpa Africana) are nursery pests. They cut seedlings and drag them into underground burrows, or left them on the surface wilting for a few days before taken them into the burrow.
The tobacco cricket may be a sporadic pest, particularly on light sandy soils where the adult crickets can easily burrow. The African mole cricket can be a pest especially at low altitudes, and particularly in moist soil.

The cotton Helopeltis or mosquito bug (Helopeltis schoutedeni)

It is a slender, delicate bug up to 10 mm long with very long antenna, nearly twice as long as the body. The nymphs are yellow with pale red markings. The adults have a red body with blackish antenna, head and wings. The eggs are white and about 1.7 mm long, and are laid into soft plant tissue.

Nymphs and adults feed on young plant tissues, injecting toxic saliva into the plant during sucking, causing necrotic patches, seen as dark brown spots, on leaves and stems. Spots exude moisture from a central puncture when squeezed. As a result the leaves are twisted and the shoots can be severely stunted. Die-back of young shoots is common under heavy attack. This bug is a common tea pest in all East African countries.

Aphids (Toxoptera aurantii)

Aphids occur in groups on the buds and the undersides of young leaves. Large colonies of the aphids are mainly found feeding on seedlings causing leaf curl and defoliation They can be a major pest of tea in the nurseries. Additional damage is caused by production of honeydew, with subsequent growth of sooty moulds.

The black tea thrips (Heliothrips haemorrhoidales)

The adult thrips are about 1.5 mm long and dark brown or black in colour with whitish legs, antenna and wings. The nymphs are whitish or greenish in colour. They feed on leaves of all ages.
Attacked buds are small, crisp and are brittle (easy to break). When the damaged bud unfolds, the leaves have a brown line of dry scars (like cork) along either side of the main rib. Yellow mites cause similar corky lesions, but thrips feeding usually does not cause the leaves to curl up like yellow mite. Even a few thrips feeding on a bud can lower the quality of the bud, making the dried buds brittle and the processed tea bitter.

Attacked leaves show silvering and a fine speckling of black spots, which are the excreta of the thrips. Damaged, leaves become thicker and harder than the normal ones, duller (not shining) and having darker green colour, and may be puckered or deformed. Thrips may also feed on the surface of stems, but only near the tip of a young shoot. This stem feeding causes rough, brown dots or patches on the surface of the stem. A tea bush with many thrips is often stunted and dry. Thrips can cause economic damage mainly in periods of drought.

Tea weevils (Aperitmetus brunneus, Entypotrachelus meyeri)

Adult weevils feed on the foliage and chew the leaf edges and also bore irregular holes through the leaf surface. The larvae are the most destructive, feeding on the taproot and causing wilting, stunting, and eventual death of young plants. Stems of young plants may be bark-ringed at ground level by the larvae.
In Kenya, the tea root weevil (Aperitmetus brunneus), which is about 7-9 mm long with pale grey scales on its body, is considered a serious pest in tea nurseries. Losses of 30 to 40% are common. The tea weevil or Kangaita weevils (Entypotrachelus meyeri) occasionally defoliate young tea newly transplanted to the field.

Termites (Odontotermes spp., Microtermes natalensis, Pseudocanthotermes militaris)

Termites feed on woody roots, branches and stems. The most damaging termites are those that attack living wood. They enter through the roots and work their way upward, finally destroying the heartwood. Stem beneath the soil is ring barked and the entire root system may be destroyed. Above-ground symptoms include wilting leaves and a poorly-growing plant. They occur most frequently on newly established plantations. Severely attacked plants wilt and die. Older plants may shed leaves. In most cases only a few plants are affected. Damage by termites to roots and stems of older plants can assume economic levels. A heavy infestation of termites that attack live wood can reduce yields by 10-15%. It may even kill large mature tea bushes. Termites that eat only dead wood do not cause direct damage, but they may make the plant more susceptible to fungal diseases.

Scales

Scales are 1.0 to 7 mm long, usually green, yellowish or brown in colour and resemble shells glued to the plant. Female scales have neither wings nor legs. Females lay eggs under their scale. Some species give birth to young scales directly. Once hatched, the tiny scales, known as crawlers emerged from under the protective scale. They move in search of a feeding site and do not move afterwards. They suck sap on leaves and twigs. Their feeding may cause yellowing of leaves followed by leaf drop, poor growth, and dieback of branches. Two types of scales attack tea: soft and armoured scales.

Soft scales (Coccus spp; Saissetia coffeae) infest leaves and twigs. They cause damage by sucking sap from the plant and by excreting honeydew, causing growth of sooty mould. In heavy infestations leaves are heavily coated with sooty mould turning black. Heavy coating with sooty mould reduces photosynthesis and affects the quality of the leaves. Ants are usually associated with soft scales. They feed on the honeydew excreted by soft scales, preventing a build-up in sooty moulds, but also protecting the scales from natural enemies.

Armoured scales (Selanaspidus spp and Aspidiotus destructor) encrust foliage, the cause damage by sucking sap; they do not excrete honeydew.

Armillaria root rot (Armillaria heimii)

The fungus is confined to the soil and is normally a saprophyte living on dead stumps and roots of forest trees. However, if the root surface of the tea bush is damaged by cultivation or boring insects, the fungus can enter the roots and become parasitic. Leaves of affected bushes turn yellow and fall and sheets of white mycelium (fungal growth) can be found between the bark and the wood. The main root system rots away and the tea bush eventually dies.

Wood rot (Hypoxylon serpens)

Wood rot in tea has been reported from several countries including India, Kenya, Malawi, Zimbabwe and Sri Lanka. The pathogen implicated is Hypoxylon serpens. Significantly, all affected areas lie at or above 1500 m.
The characteristic symptoms normally appear when the bushes are about 15 to 20 years old. Suddenly, the foliage of a branch will show wilting followed by scorching. Such branches snap off easily near the base. Sometimes intact lower branches with green foliage in these bushes could snap off similarly, especially when workers walk through during field operations. The bases of such branches have characteristic black encrustations (stroma - fungal fruiting bodies containing spores). The pathogen appears to be disseminated mainly through pruning knives and the infection progresses from pruning cuts during wet weather. Under natural field conditions, infection at 60-90% and over 90% could bring about 27 and 36% yield reductions, respectively, showing that the disease can cause significant damage.

Branch and collar canker (Phomopsis theae)

The first obvious symptom of attack is yellow or brown foliage on affected branches or bushes, contrasting with the green foliage of the surrounding healthy bushes. Closer examination reveals lesions or cankers at the base of branches or at the collar region of the bush. These lesions are less apparent in the early stages of infection but older cankers are easily recognisable by their raised margins due to the development of callus.
The diseased areas may be regular or irregular in shape, often sunken, and grey to black in colour. The underlying dead wood can be seen by scraping back the bark using a knife. In instances where the branch or the collar is completely girdled (ring-barked), a thick ridge of callus forms at the upper margin of the canker. The fungus can also infect apparently uninjured succulent green shoots, causing small local lesions. This can lead to the death of the whole shoot. Tea plants are most susceptible when they are less than 8 years old.
The disease is enhanced by drought conditions, deep planting, planting in gravelly soils, mulching close to the collar, wounds by weeding implements, low moisture status in the bark and surface watering during dry weather.

Brown and grey blight (Colletotrichum coccodes and Pestalotiopsis theae)

These fungi are considered weak pathogens and usually only affect plants that have been weakened by improper care or adverse environmental conditions. Often they occur together.
The diseases are favoured by poor air circulation, high temperature, and high humidity or prolonged periods of leaf wetness. When young twigs of susceptible cultivars are cut and used to root new plants, latent mycelium (fungal growth) in the leaf tissue may start to invade nearby cells to form brown spots, and this may lead to death of leaves and twigs.
Symptoms consist of small, oval, pale yellow-green spots first appearing on young leaves. Often the spots are surrounded by a narrow, yellow zone. As the spots grow they turn brown or grey, concentric rings with scattered, tiny black dots become visible and eventually the dried tissue falls, leading to defoliation. Leaves of any age can be affected. The tiny, black spots on the lesions contain the fungal spores. Rain splash transports the spores from one plant or site of infection to another. If the spores land on a leaf, they germinate to start a new leaf spot or a latent infection.