Coffea leaf rust (Hemileia vastatrix)

It is the major disease in Arabica coffee. Yellow to orange powdery blotches appear on the underside of leaves, chlorotic patches appear on the upper side. They grow from 2-3 mm diameter to several centimetres. On older leaves, several lesions can merge together. This produces irregular diseased areas covering much of the leaf. However, diseased leaves are usually shed before this stage. A major effect of coffee leaf rust is that it causes defoliation. The disease is spread by spores from lesions on the underside of leaves by wind and rain. Under humid conditions, hyper-parasitic fungi such as Verticillium lecanii grow over the lesions, which produces a pale mycelial growth. Leaf rust is favoured by wet, warm weather. Rainstorms of 7.5 mm or more are needed to cause disease outbreak.

The coffee berry disease (Colletotrichum kahawae)

Colletotrichum kahawae of Arabica coffee only occurs in Africa, and causes major damage in East Africa and Cameroon. Other names of this disease are "coffee berry anthracnose" and "brown blight of coffee". The characteristic symptom is a progressive blackening of young, expanding coffee berries. This begins as small water-soaked lesions. They rapidly become dark and sunken. As they grow they cause the whole berry to rot. Under humid conditions, pink spore masses become visible on the surface of the lesion.
Berries often drop from the branch at an early stage of the disease. This is a characteristic feature of coffee berry disease. Lesions may also occur on young berry stalks, causing them to be shed before lesions are visible on the berry itself. The disease also affects ripening berries causing a 'brown blight' phase. This phase is characterised by typical dark, sunken lesions that envelop the red berry.
The coffee berry disease may also infect flowers under very wet conditions, and causes brown lesions on petals. This disease does not kill trees, but crop losses can be more than 80%. Spore dispersal within the tree is by rain splash. Disease spread from tree to tree and from farm to farm is by coffee pickers, birds or infected seedlings. Wet conditions and temperatures between 15 and 27.7° C favour disease development.

Armillaria root rot (Armillaria heimii)

Symptoms include wilting of leaves, death of verticals and subsequent death of affected trees. The root system of affected trees shows a white growth (mycelial) of the fungus beneath the bark. In advanced stage of the disease the wood of the affected tree is decomposed into a white, wet mass with characteristic black zone lines running through the wood tissue. Vertical cracks may occur at the base of the stem at this stage. Initial infection in coffee plantings usually can be traced to shade trees or woody debris (stumps or old roots of shade trees) left in the ground when land is cleared before coffee planting.

Coffee wilt (Fusarium xylarioides)

Indicative symptoms include wilting, chlorosis and defoliation of the aerial parts of the crop, and numerous vertical and spiral cracks in the bark of the trunk. Inspection under the bark, especially around the collar, will reveal characteristic blue-black streaks in the wood. Fungal fruiting bodies (stromata) producing spores can be observed in the bark. Infected berries turn red and appear to ripen early. Seed infection causes blue-black discolouration of the parchment and silver skin. Spores are spread by wind, rain and through human activities (harvesting, pruning etc.). The pathogen can penetrate through wounds so any agency causing wounds will aid the spread of the fungus. Insects may also spread the disease from tree to tree.

Seed from infected berries may contain the pathogen and seed-borne infection is one way in which the disease is spread. Seedborne infection is responsible for seedling blight where the cotyledons fail to unfold, the stem becomes necrotic and the seedling dies. Infected seedlings often survive the nursery stage and later develop collar rot.

The fungus is soil-inhabiting and can penetrate through wounds in the aerial parts or superficial roots. The incubation period from first symptoms to death of the tree varies from days in young plants to 8 months in trees more than 10 years old, although most affected trees die 2-3 months after initial symptoms are observed.

Damping-off diseases (Rhizoctonia solani and Pythium spp.)

Damping-off affects coffee-seedlings in nurseries. It is caused by a complex of soil-inhabiting fungi such as Rhizoctonia solani and Pythium spp. It should not be a problem in well-maintained coffee nurseries. Factors that predispose plants to attack include over watering, over shading and acid soil.

Bacterial blight of coffee (Pseudomonas syringae pv. garcae)

Bacterial blight of coffee (BBC) is confined to a few coffee growing areas in Kenya (Solai in Nakuru District and around Mt. Elgon). Recently a few cases have been reported in the East of Rift Valley.

This bacterium is favoured by cool wet weather. Lesions appear on leaves with water soaked margins at start of infection. Leaves eventually dry up and roll inwards turning brown. Dead and dried leaves do not shed but remain attached to the plant. Symptoms occur on secondary or tertiary branches and in severe cases the heads may be affected. On twigs the terminal bud is attacked. Infection then extends downwards, resulting in dieback. Flowers and pin-heads shrivel and turn black.

The initial symptom is the blackening of a node often accompanied by blackening of the petiole and basal part of the leaf. This leads to death of the branch above the node and leaves on the branch turn brown and eventually necrotic (burnt). Severely affected trees appear scorched as if by fire. The bacterium persists on leaves, berries and on green and matured bark. During cool, wet weather, the bacterium multiplies and initiates an epidemic. The entire crop may be lost.

Fusarium Bark Disease (Fusarium stilboides)

Not widely spread in Kenya except in Taita Taveta District and Makuyu area in Eastern Province. It occurs in 3 different forms and not necessarily all forms present at the same time:

1. Storey's Bark Disease (most common). Suckers attacked at base causing depressed dark brown lesions with yellow margins at times. Pink spore masses are sometimes seen on lesions, which girdle the stem. Girdled old suckers at times continue growing with constriction of bottle neck at base. Weakened suckers may break from wind or picking.

2. Scaly bark (second most common). Bark of the tree rises up in flakes on mature stems. Cankerous regions may develop and die back can follow, though affected stems could also survive.

3. Collar rot. Infection spreads downwards from infected suckers, gradually girdling the tree base. Cankerous lesions develop round stem base at soil level. Constriction appearance may occur and die-back begin from top of tree. Mulching too close to the stem may cause similar rot. Soil- borne fungi may cause seedlings in the nursery to die in the same manner.

Fusarium Root Disease (Fusarium solani)

This fungus may stay in the stem and roots for years without symptoms until whole tree suddenly dies. The fungus enters through wounds on roots caused by ploughing, herbicides, die-back, frost or water logging. Symptoms appear when tree is subjected to water stress. If stem is cut near soil level, a purplish pink stain is seen. Dry rot will also show at centre of wood if infection has stayed long. This disease does not spread from tree to tree.

The coffee berry borer (Hypothenemus hampei)

It is the most serious pest of coffee in many of the major coffee-producing countries. Crop losses caused by this pest can be severe, ranging from 50 to 100% of berries attacked if the pest is not controlled. The adult is a tiny (about 1.5 to 2.5 mm long), cylindrical blackish beetle. The females (1.4 to 1.6 mm) penetrate into mature green or red berries, usually from the tip and lay eggs within the beans. Female beetles fly from tree to tree to lay eggs. Once the eggs hatch, the larvae feed on the beans, rendering them unsuitable for commerce or greatly lowering their quality. The white, legless grubs have a brown head. They feed by tunnelling in the tissues of the beans destroying them. Pupation takes place in the berry. Symptoms of attack are one or more small round holes near the apex of large green or ripe berries. The damaged beans, which have a distinct blue-green staining contain up to 20 grubs. Female beetles also attack young berries.
Coffee berry borer damage predisposes the coffee bean to fungal infection and hence contamination with mycotoxins (food poison). Reasons for the infestation with coffee berry borer can be: the plantation is at a too low altitude, too much shade or that there are abandoned or infested plantations nearby. Infestations are carried over between peaks of fruiting by breeding in over-ripe berries left on the tree or fallen to the ground.

Soft green scale (Coccus alpinus/ C. viridis)

Various species of scales attack coffee in East Africa. The soft green scales are common but minor pests of Arabica coffee. More serious on transplanted seedlings during the first 2 years in the field. The yellowish to greenish flat oval scales are about 5 mm in length. They prefer to attack green wood and leaves, and usually appear as rows of flat oval green scales along main leaf vein and near tips of green shoots. Soft green scales produce large amounts of honeydew. This honeydew attracts ants, which while tending the scales protect them from their natural enemies. The sticky honeydew covers the leaves and sooty mould develops on it. As a result leaves appear black and sticky. Too dry microclimate favours infestation with soft green scale.

Coffee thrips (Diarthrothrips coffeae)

The adult thrips are 1-1.5 mm in length and grey-brown in colour. The nymphs are wingless and yellow. Both adults and nymphs feed on the underside of leaves, but in severe infestations they also attack the upper side of leaves, berries and green shoots. Attacked plant parts show irregular grey or silvery patches covered by numerous tiny black spots, which are the excreta of the thrips. In case of severe infestation the leaves dry up and fall off. Heavy outbreaks occur during periods of drought and high temperatures.

Lace bug (Habrochila placida)

This bug is (about 4 mm long) and has wings with a lace-like pattern, hence its common name. The nymphs have knob-like projections on the head of the body. Both adults and nymphs suck on the leaves. Nymphs always feed in groups on the underside of the leaf. Their feeding causes yellow patches on the leaves. The underside of affected leaves is covered with spots of black liquid excreta. In case of severe attack the leaves turn yellow and drop-off. This bug is a sporadically severe pest in Kenya and Tanzania, causing severe defoliation. The attack is often first confined to the lower leaves of a small group of coffee trees. They are most common in hot dry weather. Outbreaks have been associated with injudicious use of pesticides.

Coffee berry moth (Prophantis smaragdina)

The adult is a small golden brown moth with a wingspan of about 1.3 mm. The female moth lays scale-like eggs singly on or near green berries. The caterpillar is reddish to pink in colour with dark markings on the back, and measures 13 mm when fully grown. Caterpillars bore into green, half-grown berries, starting near the stalk and hollow them out. One caterpillar usually attacks several berries in 1 cluster. Attacked berries turn brown to black. When 1 bean has been eaten, it leaves the berries and wanders over the cluster of berries joining them with threads of silk before boring into a second berry. Flower buds and the tip of suckers may also be attacked. Caterpillars pupate on the ground between dry leaves. Occasionally severe attacks occur at low altitudes. Frequently slight damage by the berry moth is considered beneficial since it has the effect of thinning out overbearing branches.

White coffee borer (Anthores leuconotus)

Adult beetles of the white coffee borer (also called white stemborer) are about 3 cm long and have very long antenna. They are dark brown greyish in colour; the wing cases are greyish white with dark markings near the end. Adult beetles feed on the bark of branches, causing little damage. Female beetles lay eggs on the trunks of trees usually at the base near the ground level. The whitish, legless larva burrows into the bark and the wood of the trunk and main roots. The larva pupates in a large chamber within the trunk. The attack by larvae causes serious damage, particularly if the trunks are almost ring-barked. Young trees may be killed.

Older trees wilt, turn yellow and produce a poor crop. Symptoms of attack are round exit holes of the adult beetles in the trunk and wood shaving extruding from the bark or from the roots just below soil level. The white borer can become a serious pest especially below 1500 m (5000 ft) on shallow or eroded soil near shade trees.

The red coffee mite (Oligonychus coffeae)

The red coffee mite may be a pest of unshaded coffee in localised attacks during the dry season. They attack the upper surface of mature leaves. As a result the upper surface of fully hardened leaves turn a rusty, purple or yellow brown colour. Under drought stress young leaves may also be attacked.

Root-knot nematodes (Meloidogyne spp.)

Important nematodes attacking both Arabica and Robusta coffee are Meloidogyne arenaria, Meloidogyne decalineata and Meloidogyne incognita, causing root knots and galls. Other nematode species include Pratylenchus coffeae, Radopholus similis, Rotylenchus iperoiguensis and Rotylenchus pararobustus.

Antestia bugs (Antestiopsis spp)

Antestia bugs are major pest of Arabica coffee in East African countries. The adult bug is shield-shaped, about 6 to 8 mm long and strikingly coloured dark brown with orange and white markings. They hide in berry or flower clusters. Females lay eggs in groups of about 12 on the underside of leaves. Newly hatched nymphs are about 1 mm long. Nymphs resemble the adults in colour but have a more rounded shape and lack functional wings.

Both adults and nymphs cause severe damage to green berries by feeding and indirectly by the transmission of a fungus (Nematospora coryli), which causes rotting of beans. The bug also attacks flower buds and shoots causing blackening of flower buds with no flower/fruit set. Attacked branches grow side shoots (fan branching). No visible surface marks / scars or wounds on berry are noticeable until seen on drying beds as "zebra" beans. "Zebra" beans produce poor quality coffee and are possible avenues for fungal infection. Antestia bugs can live on shrubs belonging to the same family as coffee (Rubiaceae family).

Capsid bug (Lamprocapsidea (Lygus) coffeae)

The capsid bug is a serious pest in all areas. The adult bug is green or brownish and about 0.7-0.8 mm long, and has a sharp downward bent in its wings, which is highly characteristic. Females insert eggs into flower buds, and thus eggs are not visible. Nymphs are pale green and pear shaped. Wing buds are visible on older nymphs. Both adults and nymphs feed on flower buds, but when they are not present they would feed on any soft green part of the coffee bush. As a result of feeding flower buds blacken due to death of stamens and petals. The style however remains healthy and usually takes a club shaped appearance with pale green shaft and black head. Damaged flowers do not set fruit. This bug is frequently considered beneficial on unshaded coffee at lower altitudes since the pruning effect of the damage caused by this bug reduces the tendency to overbear.

Leafminers (Leucoptera meyricki and Leucoptera caffeina)

The adults of leafminers are very small (3-4 mm long) white moths. They lay very small eggs (just visible to the naked eye) on the upper leaf surface scattered in small groups (L. meyricki) or touching each other in a neat row along a main vein (L. caffeina). Upon hatching, the caterpillars bore into the leaf and mine just below the upper leaf surface. The mines of each L. meyricki caterpillar are initially separated but after few days they join to form one large mine. The young caterpillars of L. caffeine produce one communal mine. These mines appear as irregular brown blotches on upper side of leaves, which when opened reveals many whitish caterpillars.

Caterpillars are flattened, white and very small (4-8 mm when fully grown). Mature caterpillars come out of the mine and pupate in a H- shaped cocoon (6 mm long) on dead leaves on the ground or on the underside of leaves on the tree.

The mining activity causes a reduction of the active leaf surface, reducing assimilation. Attacked leaves are usually shed prematurely. Leafminers can live on shrubs belonging to the same family as coffee (Rubiaceae family).

Leaf skeletoniser (Leucoplema dohertyi)

The leaf skeletoniser is normally a minor pest but severe outbreaks could occur especially in nurseries.

The adult is a grey and brown moth with a wing-span of about 1.3 cm. It is often found on leaves during the day with the hind wings drawn back alongside of the body and the narrow forewings held at right angles to the body. They lay yellow-green eggs (0.5 mm in diameter) singly or in small groups mainly on the underside of leaves. The caterpillars are greyish white with many pimple-like projections on the body. They turn red the day before pupation. Fully-grown caterpillars are about 8 mm long. They feed on underside of the leaf, usually near the near mid-rib leaving many irregular lace-like patches.

Giant looper (Ascotis selenaria reciprocaria)

The adult is a moth with a wingspan of up to 5 cm. They vary in colour from dark brown to light grey with numerous dark grey markings. They lay pale green eggs in crevices in the bark. The caterpillars are pale grey to dark brown resembling twigs, and move with a looping motion. They are about 5 cm when fully grown. Young caterpillars usually eat pits on the upper leaf surface and older caterpillars feed on the leaf margins leaving a jagged edge. All stages of caterpillar prefer tender and young leaves but berries and large flower buds may also be attacked. Alternate hosts include groundnuts, sweet potatoes, black jack weeds as well as some tree species like Datura and Eucalyptus.

Kenya mealybug (Planococcus kenyae)

This mealybug was a major pest of coffee in Kenya in the 20's and 30's in the East Rift area, but it was successfully controlled with introduction of natural enemies from Uganda. Sporadically severe attacks occur especially in the colder months of the year. The mealybugs appear as white masses between clusters of berries and flower buds or sucker tops. They are often attended by ants, which feed on the sticky honeydew excreted by the mealybugs. Honeydew leads to growing of black sooty mould on the upper surfaces of leaves.

Root mealybug (Planococcus citri)

This mealybug is usually a minor pest of coffee, but it is potentially a serious pest. The mealybugs attack the roots where they usually live in association with a fungus (Polyporus sp.), which forms a crust over the mealybugs. Seedlings and very young trees are often free of the fungus. Attacked trees show wilting yellow leaves as if suffering from moisture stress. When affected trees are uprooted, the roots are stunted and encased in brown fungus. When the fungus is pealed off, the white mealybugs can be seen.

Damage is more prominent in dry conditions. The pest is associated with poorly established coffee. Severe infestation may lead to loss of quality, failure of berries to ripen and overbearing and die-back. Identical mealybugs have been reported on Solanum spp., Combretum spp. and Indigofera spp. The root mealybug is also known as the citrus mealybug. It also attacks citrus and cocoa, where it normally attacks the aerial part of the plants.

In the highlands of Java, the shade tree Leucaena glauca is main food plant of citrus mealybug at altitudes above 600m (2000 ft.). Measures that proved successful for the control of citrus mealybug were mainly directed against infestation of this tree and consisted of removing the flower clusters or, when necessary, pruning all foliage and flowers. It is also claimed that citrus mealybug can be controlled by increasing the shade in plantations and that this was undesirable for Robusta coffee but suitable for Arabica at high altitudes. Good results were obtained by providing three covers, one above the other, of Leucaena, Erythrina and Albizia, or with Leucaena and Albizia only. It is further suggested that because the insect infests mainly the flowers and pods of L. glauca, other shade trees that seldom flower, such as L. pulverulenta (L. leucocephala), or a sterile hybrid of L. glauca and L. glabrosa should be planted.

Star scale (Asterolecanium coffeae)

It is yellowish to reddish brown, covered with numerous small spines. It attacks stems and branches, causing deformation of branches. The growth of trees severely attacked is retarded and the trees may be die. Symptoms include green branches bent at nodes with pits in green bark beneath the bend, drooping dead leaves on affected nodes and numerous small red or yellow objects are found in the bark crevices especially near the ground. Alternative hosts include Jacaranda and loquat trees.