Most of the control measures currently in use involve the application of chemicals but one method of reducing the spread of disease is to remove and burn all infected plant material as soon as it is observed, strict attention to farm or garden hygiene is one of the easiest and most economic ways of preventing the spread of crop diseases. Where the branches of treesare observed to be infected with disease, the affected branches should be cut cleanly with a saw and not slashed with a cutlass, unless they are very thin branches. All major cuts should be trimmed smooth with a sharp knife and then covered with either a bituminous or weather-resistant paint to encourage healing of the cut surface.


The use of chemical sprays has become more widely accepted during recent years and many sprays which kill disease spores and mycelium are now available. These chemicals are generally referred to as fungicides.  The equipment used for applying chemicals in the form of dusts or sprays has been outlined.

Most fungi can be effectively controlled by the use of fungicides as sprays although some dusts, such as those containing sulphur, can also be used in some conditions. Early action is required to control an outbreak of disease, if adequate control is to be obtained. The spray should also be directed to both sides of the leaves of the plant, otherwise the infection will continue to develop.

Spray chemicals should always be mixed and used in accordance with the manufacturer's instructions which are attached to the container and containers should always be either buried or burned after use. It is also most important that the manufacturer's recommendations concerning the period which must be allowed to elapse between spraying and harvesting produce should be observed. Chemicals applied to any part of a plant are likely to persist in the leaves, fruit or seed for up to 14 days after they have been applied and these residues can be harmful to the consumer if they are not allowed to break down within the plant.

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Fungicides and applications:

The objective of applying fungicides as preventive or control sprays or dusts is to cover both sides of the leaves of the plant with a fine coating or film of the chemical used. Sprays should be fitted with nozzles of the required size to give the type of spray which is most effective and in some cases where water is scarce a very fine mist-like spray may be most suitable. An agitator should be fitted to the tank of large sprayers to ensure thorough mixing of the chemical. Spreading agents, which ensure that the film of spray will cover the leaf surface by lowering the surface tension, and 'stickers' which increase the adhesion of the droplets  to the leaf surface, are sometimes used to improve the effectiveness of the spray.

Traditional and still widely used fungicides include the following.

CHESHUNT COMPOUND, used for preventing seedlings  from 'damping off', a disease which often occurs in badly-drained and overcrowded seedling beds and containers. It consists of 55 g of copper sulphate and 310 g of ammonium carbonate. Both chemicals are finely ground, mixed and left for 24 hours before being thoroughly mixed with water at the rate of 30 g to 91 of water. The seedlings should be watered with the solution at intervals of 4-6 days.

BORDEAUX MIXTURE consists of 1.8 kg of copper sulphate, 1.8 kg of burned lime and 2251 of water. The copper sulphate is mixed with 2-4 1 of water and this solution is then made up to about 22 1 of water; it is essential to prepare this solution in a non-metallic container, otherwise corrosive chemical reactions will occur. Water is added slowly to the lime and the mixture is made up to 200 1 by adding more water; this is then well stirred. The copper sulphate solution is added to the lime water and the whole mixture is thoroughly stirred before being used.

BURGUNDY MIXTURE consists of 2.5 kg of copper sulphate and 2.8 kg of washing soda. Both chemicals are dissolved in 2.41 of water, mixed and diluted with 225 1 of water.

AMMONIATED COPPER CARBONATE is made from 140g of copper carbonate, 1.7 1 of ammonium hydroxide and 225 1 of water. The copper carbonate is made into a paste with water and added to the ammonia and the resulting mixture made up to 225 1 by adding water. This can be used as a spray on relatively young plants.

LIME-SULPHUR may be prepared by adding water to 2.25 kg of burned lime. To this is added 4.5 kg of flowers of sulphur and the mixture is well stirred. More water is added to make 181 and the resulting mixture is boiled, preferably in an iron container, until the solution becomes clear. For spraying on mature plants, 4.51 of the solution is made up to 112 1 and well stirred. Lime-sulphur will corrode copper so that containers or sprayers made of this metal should not be used.

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More modern fungicides are becoming available in some parts of West Africa, such as BENOMYL, a general fungicide which is systemic in action. This means that it is able to enter into the tissues of leaves, stems and roots so that fungi which attempt to penetrate into these tissues are soon destroyed. CAPTAN is used as a general spray or as a seed dressing. THIRAM is also used, in the form of a slurry, as a seed dressing, but is also a general purpose fungicide, particularly effective against downy mildew. Both captan and thiram can be used to control damping-off in seedlings. ZINEB controls a wide range of mildews, leaf spots and blights and is normally available as a wettable powder.

MANEB is sometimes used as a mixture with zineb and is a useful fungicide for controlling blight and some forms of leaf mould. COPPER DUSTS are available, in various forms, as general fungicides, also various types of sulphur. Some formulations of sulphur may also be obtained as wettable powders.


Common diseases of farm and garden crops include:

A. FUNGI Maize rust, corn smut, covered smut of sorghum, blast of rice, leaf spot of groundnuts, zonate leaf spot of sweet potato, cucumber powdery and

downy mildew.

B. VIRUS Tristeza virus of citrus, swollen shoot of cocoa, cassava and yam mosaic, rosette disease of groundnuts, tomato and pepper virus (several), and bean mosaic virus.

C. BACTERIA Cotton bacterial blight, bacterial wilt of tomato, peppers and bananas.

A. Fungus diseases

Gives the main characteristics of these diseases, with suggested control measures.

B. Virus diseases

Summarises the main characteristics of some important virus diseases with suggested control measures.

C. Bacterial diseases

Summarises the main  characteristics of some important bacterial diseases with suggested control measures.


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