Frequency and timing of insecticide application to control cocoa mirids

This 5-year study was cohducted at five sites on farmers' farms of mixed populations of mature hybrid and Amelonado cocoa varieties to ascertain the best time to apply the least number of chemical applications to effectively control cocoa mirids, Distantiella theobroma (Dist) and Salhbergella singularis Hagl. A plot size of 0.8 ha at each site was given treatments of lindane as Gammalin 20 at 280.g.a.i./ha in 56 1 of water as follows: (1) one application in October, (2) two applications in September and October at 2-days' interval, (3) two applications in October and November at 28 days' interval, (4) the CRIG recommended four applications in August, September, October and December, and (5) untreated control. The treatments were arranged in a completely randomised block design. Mirid population counts were taken before treatment and 48 h after treatment. Fresh mirid-damaged trees, pod and tree population counts, canopy rating, and minor pests and predatory arthropod population were also recorded. At the end of the 1st year, there was no significant difference in mirid re-infestation rates between the single application (October treatment) and the untreated control treatment, although the percent degraded cocoa trees in the former treatment was higher (13.2 per cent) as compared to 10.0 per cent in the latter. Throughout the 5-year study period, mirid seasonal re-infestation was lower in the treated than the untreated control plots, the average re-infestation rates (mirids per plot per season) being as follows in increasing order: 2.6 (CRIG 4-treatments/year). 5.7 (September/October), 8.2 (October/November), and 71.2 (untreated control). Tree canopy improved by factors of 5.0. 6.0 and 4.6, respectively for the treatments September/October, October/November, and the CRIG 4-treatments/year, but there were no significant differences among these factors whilst the untreated control plots deteriorated by a factor of 3. As regards yield, the September/October treatment had the highest mean number of pods of 2.033 per plot, and the control plots had the lowest of 1,125 pods per plot. It is recommended that two applications of lindane (Gammalin 20) per mirid season is sufficient.