OBSERVATIONS ON FUNGICIDE CONTROL OF WITCHES‘ BROOM, BLACK‐POD AND PINK DISEASE OF THEOBROMA CACAO

Abstract

Spraying experiments were started in Trinidad in 1940 and continued in Nigeria in 1950 to determine the control of certain cacao diseases obtainable by relatively frequent applications of copper fungicides, and also to test modified procedures designed to reduce spraying costs.It was found that a spray applied only to the cropping regions of the trees reduced pod losses, which may include Phytophthora and Diplodia infections in addition to witches' broom disease (Marasmius perniciosus).Experiments in Trinidad on witches' broom disease showed that monthly applications of 1% Bordeaux mixture reduced the incidence of both vegetative brooms and affected pods. The number of cushion brooms was not reduced; there was an apparent increase associated with spray applications to one particular cacao clone (ICS 4). There was no apparent advantage when the interval between spray applications was reduced to 1 or 2 weeks, because vegetative brooms occurred in spite of such frequent applications. However, if pod losses can be controlled directly, the occurrence of vegetative brooms would be unimportant.Pink disease (Corticium salmonicolor) was completely controlled by applications of Bordeaux mixture. It appeared that there was at least a 12 months' residual effect from spraying.Experiments were carried out in Nigeria on the control of black‐pod disease (Phytophthora palmivora), using carbide Bordeaux, prepared by adding solid calcium carbide to 1% copper sulphate solution. Satisfactory disease control was obtained with applications at intervals of 1–4 weeks. Perenox (0.1%) was less effective than carbide Bordeaux. Knapsack spraying failed to protect all pods more than 7 ft. from the ground.In Fernando Po, where Bordeaux mixture is used for the control of black‐pod disease, two to four applications are made per season. Black‐pod control is almost universal on plantations in Fernando Po, where there are consequently relatively few sources of infection.