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(Fusarium stilboides)

Credits: Biovision-Infonet

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.

What to do:

• Report suspected infections to CRF or coffee extension officer. For Storey’s bark disease affected suckers or heads should be cut off and burnt.
• Pruning scars should be treated with fungicidal paint or tar mixed with linseed oil.
• Disinfect pruning tools by dipping in spirit with 70% alcohol.
• Uproot and burn on the spot trees dying back from collar rot and old stumps as well as severely diseased trees if no healthy suckers develop.
• Weed around the plants without damaging the bark.
• Pay attention to soil fertility and acidity, correcting where necessary.
• Eliminate wood boring insects.

(Fusarium solani)

Credits: Biovision-Infonet

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.

What to do:

• Remove dead trees and leave hole unplanted for several months.
• Do not damage roots of new seedlings
• There is no cure for infected trees.

(Fusarium xylarioides)

Credits: Biovision-Infonet

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.

What to do:

• The use of disease-free seed is advised (from areas where the disease is not present).
• Frequent inspection of the crop, along with burning infected material and spraying the soil surface with 2.5% copper sulphate has been advocated as an effective control measure.
• Replanting should not be done until 6 months after uprooting infected trees to allow the disease in the soil to decline.

(Armillaria heimii)

Credits: Biovision-Infonet

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.

What to do:

• Where coffee has to be planted in newly cleared forest land, it is recommended that ring-barking of the forest trees be done 2 to 3 years earlier.
• Remove forest trees stumps, remove as much as possible of forest trees roots, and drench the root area with a copper fungicide
• It is not possible to save a coffee tree once infected. The infected tree should be uprooted and replanting should be delayed for 2 years.

(Colletotrichum kahawae)

Credits: Biovision-Infonet

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 27.7deg C favour disease development.

What to do:

• Plant resistant variety where coffee berry disease is endemic (e.g. ‘Ruiru 11’).
• Prune coffee trees after harvest.
• Strip off diseased berries.
• Remove old stems and thin out branches.
• Timely spray copper fungicide

(Pseudomonas syringae pv. garcae)

Credits: Biovision-Infonet

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.

What to do:

• Desucker or cut off infected twigs (at least 5 cm from the point of infection) and collecting them in buckets for burning.
• Observe field hygiene by disinfecting tools used for pruning infected trees with a suitable disinfectant such as spirits with 70% alcohol. Implements used must be sterilised after making each cut to avoid the risk of infecting the cut surfaces of the twig with a carry-over inoculum.
• Use of copper sprays especially during wet season. Spray at 2 week interval during the rains and 3 week interval after the rains.
• Plant shade trees and wind breaks on exposed sides of BBC areas.
• Avoid planting material from known BBC areas. In emergencies spray with copper just before, during and after flowering especially when this coincides with cool wet weather.