Evaluation of clove (syzygium aromaticum) and peppermint (mentha piperita) extracts as stored maize grain protectants against maize weevils (sitophilus zeamais l., coleoptera: curculionidae)

Abstract

Post-harvest losses of caused by maize weevils (Sitophilus zeamais) are a major challenge affecting maize storage among smallholder farmers. The continuous use of synthetic pesticides has raised concerns due to their costs which are not affordable, environment pollution, weevil resistance and health risks to humans and livestock. This research focused on evaluating the effectiveness of clove (Syzygium aromaticum) and peppermint (Mentha piperita) extracts as botanical protectants against maize weevils in stored SC 529 and Klein Karoo (PGS63) maize varieties. The experiment was conducted as a 2×4 factorial treatment structure, laid in a Completely Randomized Design (CRD), with eight treatments replicated three times. Grain protectant type factor had 4 levels (clove powder, peppermint powder, Shumba Plus dust as a positive control and untreated maize grain as a negative control), while the variety factor had 2 levels (SC 529 and Klein Karoo PGS63). The data collected included weevil mortality, grain damage and grain weight loss over an eight-week storage period. There was no significant interaction (P>0.05) between grain protectant and variety on weevil mortality, grain damage and grain weight loss across all the sampling periods (week 2, 4, 6 and 8). Grain protectant type had significant effect (P<0.05) on weevil mortality, grain damage and grain weight loss, with clove extract demonstrating high effectiveness against S. zeamais, achieving 96% weevil mortality after eight weeks, which was statistically comparable to the synthetic pesticide Shumba Plus dust (100%). Peppermint extract showed lower effectiveness with 54% mortality after eight weeks and also some insects were not found which indicated the repellent effect. Grain damage and grain weight loss were significantly lower in cloves and Shumba-treated maize compared to peppermint-treated and untreated maize. Untreated maize recorded the highest grain damage and weight loss of 100%. Although some varietal differences were observed, SCSC 529 showed slightly greater resistance to weevil infestation than Klein Karoo PGS63. The study concluded that clove powder is highly effective, have high affordability and environmentally friendly alternative to synthetic pesticides for controlling maize weevils in maize grain storage. The use of clove powder can highly contribute to reduced post-harvest losses, improved grain quality and enhanced food security among smallholder farmers. Further research is recommended on dosage optimization which is also the concentration of the extracts, long-term storage performance which is the period of exposure and farmer adoption of botanical pesticides.