Stem borer-attributed mortality of shea trees in Northern Ghana: Infestation, tree death and associated factors

Abstract

The shea tree is important in several African countries, supporting livelihoods and providing foreign exchange. Shea tree mortality as a result of pest infestation was reported in two parklands in Northern Ghana in June 2018. This study reports on tree mortality in the parklands with reference to stem borer infestation and related characteristics. Standing shea trees in the parklands were randomly sampled to determine stem borer infestation and its role in tree mortality. Nutrient concentration of soil and pest-infested shea were also analyzed. Stem borer infestation at Maluwe (34%) was higher than Gindabo (2%) with tree mortality of 4% and 0%, respectively. Stem borer (Philematium festivum) larvae were absent on standing shea trees but pervasive on windthrown trees. Nutrient (N, P, K, Mg) concentration was significantly different among plant parts, pest infestation status of tree and their interaction at Maluwe. However, at Gindabo, there was no significant difference in pest infestation status and plant parts-pest infestation status interaction for N and plant parts for K. At Maluwe, stem borer-infested trees had the highest N and K levels, while co-infested and un-infested trees had the highest P and Mg levels, respectively. However, un-infested trees contained the highest nutrient levels at Gindabo. Soil characteristics of both sites were similar and although soil nutrient levels at Gindabo were relatively higher, the shea trees had lower nutrient accumulative potential. The reported death was due to abiotic factors including wind/storms that predisposed the trees to proximate factors such as stem borers.