Fertilizer Application, Pests and Diseases Control in Cocoa
Common pests on cacao area: termites, caterpillars, aphids, mealy-bugs and capsid bugs. They are more prevalent during the dry season. Insecticides as: Gammalin, Aldrex, Aldrin etc., should be used at the recommended dosages.
Common diseases;
1. Black Pod Disease
About 40% of annual Produce is lost this disease. The causal agent is a fungus called Phytophtora palmivora.
Symptoms — Small brownish spots with irregular fringes looking as though it is wet appear on he leaves. This spots gradually increase in size and in about 2-3 days later, a whitish downy mould (mycelium) is found in the centre of each spot.
In about 3 weeks, the whole pod is covered, while chileos (baby cocoa pod) are covered within 3-4 days.
The whole pod turns black while the chileo becomes shriveled
Spread/Etiology. The mycelia contain many millions of spores which are tiny and light. The spores are splashed during rainfall and thus spread.
The spores do not germinate unless the conditions are right — the climate is humid.
Control:
Use of chemicals—fungicides. E.g. copper sulphate, Bordeaux mixture, Perenox, Perepod, Lime on Carbide.
Removal of infected pod and burn or bury.
Reduction of humidity through pruning.
2. Swollen Shoot
This is a virus disease caused by Pseudococcus njalensis and Pseudococcus citri; Ferisiana vulgata or Ferisiana valensis.
The virus is transmitted by mealy bug. The virus is prevalent on Sterculiaceae family —cacao and cola.
Symptoms:
Swellings on roots and branches
Stunted growth.
Leave necrosis and chlorosis
Small and roundish pods
Control
Elimination of infected trees.
Elimination of surrounding healthy trees within a radius of 5 – 15 metres of the infected tree.
Elimination of vectors.
Fertilizer Application
Where the soil fertility is in doubt, complete fertilizer can be applied. The recommended complete fertilizer is 15-15-5 or 15-15-10.
An old mature plantation however needs lots of phosphorus to maintain high level fruit level. Where complete fertilizers are not available, phosphorus is recommended.
Read Also : Propagation Of Cocoa Trees: Field Operations
1. Phosphorus requirement for growing cocoa
Phosphorus is vital for the growth processes of cocoa trees but only a small quantity is required. In most soils, incorporation of phosphate in planting holes gives a significant improvement in early growth.
One reference suggests that cocoa growing soils must have certain anionic and cationic balances, including:
The optimum total nitrogen/total phosphorus ratio should be close to 1.5, with the assimilable phosphorus content being at least equal to 180ppm of P or 0,229 per thousand of P2O5.’
Another reference estimates the phosphorus requirements of cocoa plants (based on 1,075 trees per hectare) as follows:
| Stageof plant development | Range of age of plants(months) | Average Prequirement in kgperhectare |
| Seedling | 5-12 | 0.6 |
| Immature | 28 | 14 |
| First year production | 39 | 23 |
| Mature | 50-87 | 48 |
Phosphorus deficient plants show signs of stunted growth. The mature leaves are paler at the tips and margins which is followed by tip and marginal scorch. Young leaves are reduced in size, often showing interveinal pallor, and are at an acute angle with the stem.
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