Some research bearing on the control of pod rot of cacao caused by Phytophthora palmivora

Sources of primary inoculum of Phytophthora palmivora being in the soil beneath the trees, in diseased cushions, in old diseased pods, and in leaf lesions, it can be assumed some primary inoculum is present in most cacao plantations all the year round. This makes spraying for pod rot advisable whenever weather and host conditions stimulate the fungus into activity. Since the number of hours of wetting and of reduced temperature are the chief stimulants to the fungus, it follows that the timing of spray applications should be geared to the amount of rainfall with its usual temperature reduction rather than to the calendar. In Costa Rica applications of KOCIDE, a stabilized copper hydroxide, when made every time six to eight inches of rain had accumulated, were much more effective than applications made every time 10 to 12 inches of rain had fallen. The latter program did not pay for itself. Also since in Central America about 90 per cent of the crop often comes form 60 per cent of the trees, and 50 per cent of the trees may produce less than ten pods a year, and since it does not pay to spray even to double such low yields, it is tentatively suggested to spray only the trees with over ten pods on them, at least in some years after bringing the plantation up to its full potential production. It costs no more to spray and double the yield of high producing trees than low ones and it pays much better. Excellent control of Phytophthora leaf blight and of Colletotrichum leaf spot were obtained in well replicated plots of seedlings in the nursery with and organic fungicide Ortho Difolatan, a tetrachloroethylthio cyclohexene dicarboximide. The possible role played by Phytophthora in the complex known as die-back on cacao is indicated by preliminary experiments at Turrialba