Impact of pruning intensities on cocoa tree productivity, pest (mirids) and disease (black pod disease) infestations on farmer field trials in Côte d'Ivoire

The current study was carried out to evaluate short term effects of pruning intensities on fruit set, pod health and yield responses in mature trees of 10 to 15 years old. Two different pruning intensities (Removal of 20% removal of secondary branches and removal of 40% of secondary branches) were compared to unpruned trees (Control). We investigated also whether effects of pruning intensities vary across agroecological zones (deciduous and evergreen forest zones). Five cooperatives distributed in two agroecological zones were selected (two in deciduous zone and three in evergreen forest zone). Five trial sites were installed per cooperative each with the 3 pruning treatments (unpruned Control, 20% pruning and 40% pruning). Pruning treatments were applied the first time in April 2020 then renewed in April 2021. Various observations on yield parameters i.e., pod size, number of pods (healthy, mirid infected, black pod infected), number of beans per pod, fresh bean weight and dry bean weight were recorded for each plot at every harvest event (started in main crop 2020) for both light and main crops. 

Experiment results revealed that during the first year of trial (20/21 crop season) both pruning intensities increased dry bean yield. However, the lighter pruning intensity (20% pruning) was more suitable in transitional zone as it showed higher yield (648.5 Kg/Ha) compared to heavy pruning (40% pruning and 591,2 Kg/Ha) and unpruned control (522Kg/Ha). In evergreen forest zone, heavy pruning showed higher yield (890,5 Kg/Ha) compared to light pruning (832,5 Kg/Ha) and unpruned control (742,4 Kg/Ha). During 21/22 main crop both pruning intensities delivered comparable yield results in the two agroecological zones (600 Kg/Ha) but were still higher than unpruned control (500Kg/Ha). Pruning decreased mirid (52% and -60% respectively for 20% and 40% pruning intensity) and black pod -Phytophtora (-43% and -45% respectively for 20% and 40% pruning intensity) infestations over crop seasons. 

Our results confirmed that pruning is a key lever for reducing mirid and black pod disease infestation and improving productivity which contributes to increasing farmer income. Our findings showed also that light pruning is suitable in transitional zones when starting the implementation. Finally, by improving pod health pruning could contribute to improvement of beans quality by reducing the level of free fatty acids (FFA) that are favored by fermentation of poor-quality beans. The link between pruning and improvement of bean quality and potential for reducing FFA level is currently being investigated on our trial sites. 

Keywords: pruning, mirids, black pod disease, yield, cocoa productivity