Efficacy of aqueous extracts of Aloe zebrina Baker, Capsicum annum L. and Melia azedarach L. against Aphis gossypii Glover (Homoptera: Aphididae)
By: Rangarirai Mapuranga, Francis Jimu, Fredy Musiniwa, Simbarashe Muzemu, Tendai Madanzi
Key Words: Aphids, Biopesticides, Botanical, Efficacy, Repellence.
Int. J. Agr. Agri. Res. 9(2), 36-46, August 2016.
Low cotton yields in Zimbabwe are mainly caused by infestation by high numbers of insect pests, diseases, poor agronomic practices and poor season quality. Aphids cause considerable yield loss in cotton. Control methods implemented for aphids include cultural approaches, chemical and biological control and use of biopesticides. Synthetic pesticides used by farmers have problems of environmental contamination, toxicity to non-target organisms, resistance by pests and toxicity to humans among others. Plant extracts (PEs) are suitable alternatives to synthetic pesticides. Three aqueous PEs at 10 and 20%v/v application rates, distilled water (no spray) and acetamiprid were evaluated against aphids. The 3×2 factorial + 2 experiments were laid out in an RCBD in the field and CRD for laboratory experiments. Leaves of Aloe zebrina and Melia azedarach and Capsicum annum fruits were dried and ground into powder. Water extracts were prepared and used at 10 and 20%v/v and compared with synthetic insecticide and distilled water in the laboratory. In field evaluations distilled water was replaced by unsprayed plots. All three PEs had insecticidal properties against aphids. During laboratory experiments C. annum 20%v/v killed 64.75% aphids and C. annum 10%v/v killed 63.85% aphids and they were significantly (p=0.007) different from other treatments after correcting for mortality. An average of 80.3% and 72.2% aphids were controlled by C. annum 20%v/v and A. zebrina 20%v/v during field trial, these were significant (p<0.001). A. zebrina extracts had both repellence and contact toxicity against aphids. All the PEs are suitable alternatives to aphicides for aphid management.