Shade trees, disease and cocoa production in Western Ghana – a case study

Abstract
This research addresses the impact of shade trees on smallholder cocoa agroforestry systems from Western Ghana. Improving agroforestry systems in cocoa production has the potential to address the increasing pressure for sustainable cocoa while improving farmers’ food security and income diversification. Many different approaches to this problem can be taken. In this study, the effect of shade tree canopy cover was tested on productivity of individual cocoa trees (represented by harvested pod counts) and on disease and pest damage (represented by the presence of mirid damage and black pod). A potential interaction between disease/pests and productivity was also measured as the percentage of pods lost to disease and pests. Finally, the preferences of farmers regarding shade tree species were also addressed to reveal additional benefits of shade trees to cocoa farmers.
18 plots were assessed in this study with varying shade levels (0-90%). Shade tree cover did not have a significant effect on the number of harvested cocoa pods or the number of viable pods, while the number of mature pods before harvest was negatively affected by shade. The percentage of harvested pods that were viable was also not significantly affected by shade and the percentage of harvested pods lost was around 15%.
Shade only significantly increased the percentage of mature pods with black pod per tree while mirid damage was not affected by shade. Young pods (cherelles) had a smaller percentage of damage by mirids and black pod than mature pods.
Farmers participating in the survey (n=6) made use of shade tree products and acknowledged their economic benefits. They also had preferences for shade tree species and were aware of benefits and disadvantages associated with them. Some answers were not described in literature, such as increased pest/disease incidence caused by M. excelsa, use of N. laevis in yam plantation and two local tree names mentioned as undesirable.
It is concluded that shade tree cover did not significantly affect productivity of cocoa trees or the losses associated with disease and pests in the late development stages of cocoa pods. Additionally, the small sample of farmers noted benefits of shade trees in income diversification, food security and improved cocoa production. Therefore, no significant reason is presented against the potential benefits of shaded systems. Contrastingly, increased shade led to an increased spread of black pod within infected trees, although shade did not increase the incidence of black pod per plot, suggesting that high shade does not increase the spread of black pod to neighbor trees. Therefore, effective pruning and removal of diseased pods should decrease the differences between shade levels. In general, disease and pest counts should focus on immature pods and the causes leading to cherelle wilt, in order to draw better relationships between shade, disease/pests and productivity.