Control of bark canker in cocoa with metalaxyl

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Abstract
Some previous treatments for Phytophthora bark canker of cocoa, in Papua New Guinea and elsewhere, are summarised and the new systemic fungicide metalaxyl, other non‐systemic fungicides and removal of outer bark by scraping are compared. Details are given of inoculation and reisolation techniques which gave rapid and reliable results for the study of cocoa canker. Metalaxyl was much superior to the other treatments under the conditions of these experiments and 0.25% a.i. metalaxyl effectively controlled P. palmivora in artifically induced cankers. Bark cankers very often start around bark damage made by the larvae of woodboring insects and 0.25% a.i. metalaxyl added to an aqueous dichlorvos/white oil mixture used to control these insects was also effective in eliminating the fungus. It was considered that scraping followed by natural desiccation, which effectively controls canker in W. Malaysia, would not be reliable under the wetter climatic conditions in Papua New Guinea. The current recommendations for canker control are given based on the above results.