Influence of farmer’s agronomic practices and weather factors on abundance and impact of spodoptera frugiperda and its natural enemies in maize fields in Uganda

Abstract

Spodoptera frugiperda (Lepidoptera: Noctuidae), commonly known as fall armyworm, was first detected in Uganda in 2016 and has spread to all the maize-growing districts. Different methods have been deployed to control this pest. However, there is a limited understanding of the role of the environment and farmers’ practices on the abundance of and damage by S. frugiperda in Uganda. This study, therefore, assessed the abundance of S. frugiperda and leaf damage levels in three different districts and explored the association between agronomic practices, crop phenology, and weather parameters on S. frugiperda damage and abundance in smallholder farmers’ maize fields using a longitudinal monitoring survey in 69 farmers’fields of Kole, Kiryandongo, and Nakaseke for three seasons. The numbers of egg masses and adults were generally low. The highest numbers of adults were trapped in Kiryandongo, followed by Nakaseke, and the lowest numbers were trapped in Kole. Leaf damage and incidence of damaged plants differed significantly between districts and seasons. Leaf damage and abundance of larvae varied significantly in the districts and at different growth stages. Rainfall, maximum temperature, minimum temperature, average temperature and cropping system were significant for larval abundance. Conservation tillage, reduced weeding frequency, increased rainfall and maximum temperatures were associated with reduced S. frugiperda damage. No significant relationship was observed between pesticide with S. frugiperda leaf damage. However, the influence of fertilizer use on leaf damage was contradictory across seasons and district In total, five parasitoid species were recovered from S. frugiperda: Telenomus remus Dixon, Coccygidium luteum (Brullé, 1846) with 100% nucleotide identity, Cotesia icipe Fernandez-Triana and Fiaboe, and Charops cf. diversipes with 100% nucleotide identity, Tachinidae sp. 2 AS-2017 with 99.67% nucleotide identity. There were significant negative relationships between the abundance of earwigs and temperature (both minimum and maximum). However, there were no significant relationships between the abundance of each S. frugiperda studied natural enemy species with all management practices and weather factors. Timely and vigilant scouting, proper timing of control measures, minimum tillage practices, and crop diversity can be included in an IPM strategy in the management of S. frugiperda.