Efficacy of Three Doses of Fungicide Ridomil Gold 66 WP in the Control of Phytophthora spp., Agent of Cocoa Tree Black Pod Disease in Côte d'Ivoire

Black pod disease is a major constraint to cocoa production in Côte d'Ivoire. Varietal selection and fungicide treatments are the principal means of control. Fungicide Ridomil Gold 66 WP (6% Metalaxyl and 60% copper oxide) is commonly used. This study aimed at evaluating the effectiveness of three doses of Ridomil Gold 66 WP in the control of black pod disease. An experiment on the rates of this fungicide was conducted in two localities (Aboisso and Duékoué). The experimental design was a randomized complete block with four treatments, replicated four times. The treatments comprised untreated or controlled, single dose (3.3 g/l) or recommended dose, double dose (6.6 g/l) or 2×recommanded dose and triple dose (9.9 g/l) or 3×recommanded dose. All data collected were subjected to ANOVA with the test of Student and Newmann-Keuls at the 5% threshold. As result, no significant difference was observed between the treatments of the three doses of Ridomil. But, a significant difference was observed between the fungicide treatments and the control. In Duékoué, black pod rates ranged from 4.5 to 9.52% in fungicide treated plots against 33.8% in control plots. In Aboisso, black pod rates ranged from 7.11 to 13.83% for fungicide treated plots against 30.83% for the control plots. Fungicide treatments increased healthy cocoa pod yields in both localities. The yields were increased by 51.35 to 89.63% in treated plots of Aboisso and by 34.63 to 101.06% in treated plots of Duékoué. This study confirmed the efficacy of the recommended dose (3.3 g/l) of Ridomil Gold 66 WP in the management of black pod disease. Yet, even if high doses of Ridomil Gold 66 WP improved yield, it could also be led to the development of resistant strains of Phytophthora spp. and increase production costs.