Evaluation of alternatives to synthetic pesticides under small-scale farmer-managed grain storage conditions

Abstract

Reducing farm-level grain storage losses for small-scale rural farmers is important for sustainable household food security in Africa. Farmer-managed trials were conducted over two 32-week grain storage seasons in Zimbabwe to evaluate the effectiveness of diatomaceous earths (DEs); Protect-It® and Chemutsi (raw local DE), enhanced with low doses of deltamethrin or spinosad as protectants of stored maize grain for control of major storage pests: Sitophilus zeamais, Prostephanus truncatus, Tribolium castaneum and Sitotroga cerealella. Five combinations of DE-spinosad and DE-deltamethrin were compared against a commercial insecticide mixture of pirimiphos-methyl + deltamethrin and an untreated control. Treatment effects on insect numbers, grain damage and weight loss, and grain moisture content were assessed at 8-week intervals. Protect-It® 0.1% + deltamethrin 0.0005% w/w, Protect-It® 0.05% + spinosad 0.005% w/w, and Chemutsi 0.1% + spinosad 0.0075% w/w were the most effective (P < 0.001) treatments when all efficacy parameters were considered. These low-dose DE-based combinations have potential to replace organophosphate-based commercial grain protectants currently used in small-scale grain storage systems and thus contribute towards improved household food security and safety in Africa.