Efficacy of metal silos and hermetic bags against stored-maize insect pests under simulated smallholder farmer conditions

Abstract

Pesticide-free hermetic grain storage is an environmentally-benign alternative to synthetic pesticides, currently being used in many countries. However, in some African countries knowledge gaps exist on the effectiveness of hermetic maize storage, particularly where the Larger Grain Borer (LGB), Prostephanus truncatus occurs. Trials simulating African smallholder farmer conditions were conducted at two sites in contrasting agro-ecological zones in Zimbabwe for up to 12 months during the 2013/14 storage season. There were two hermetic treatments: metal silos and hermetic bags; and two non-hermetic treatments: a registered synthetic pesticide and untreated control, in polypropylene bags. Two modes of infestation: natural and combined (natural plus artificial) were used as factors. Treatments were arranged in a completely randomised design and stored in ordinary rooms. Hermetic treatments were significantly superior (P < 0.001) to non-hermetic treatments in preserving germination, controlling insect population development, suppressing maize grain damage, controlling grain dust production and consequently limiting weight loss during storage. Hermetic bags were more effective than non-hermetic treatments in reducing storage losses despite the plastic liners having multiple insect-induced perforations of more than 300 holes per plastic liner at termination. However, there were no significant differences between metal silos and hermetic bags regardless of the mode of infestation. There was strong correlation between total insect population per kg and: percentage grain damage, percentage weight loss, and grain dust which indicate the importance of controlling insect pest development during storage to reduce losses. Results show that hermetic storage can be an effective pesticide-free alternative to synthetic pesticides in reducing grain storage losses under smallholder farming conditions, even where LGB occurs.