Potentiel of threshold-based interventions for cotton pest control by small farmers in West Africa

Two types of threshold-based pest control schemes for cotton have been introduced by CIRAD, in collaboration with national research institutions in West Africa, to escape the traditional calendar-based spraying programme. In the first type (in Benin, Cameroon and Guinea), insecticides are still applied according to a calendar (5 or 6 sprayings at fortnightly intervals), but formulations and dosages depend on the pests observed on the day before spraying. In the second type (Faso, Mali, Senegal and Togo), insecticide is applied at a lower dosage than in the usual calendar-based programme and scouting is performed 6 days after spraying. Further spraying is performed on the next day if the threshold has been attained. Specific procedures depend on the country (sampling plan, insects considered as key-pests): spraying thresholds and active ingredients may vary according to these features. The main benefits of this approach are ecological and economic. A 40-50% reduction in pesticide consumption reduces the protection cost from US$50/ha to less than US$30/ha. Accurate timing of spraying results in a 100-200kg/ha increase in seed-cotton yield. Many constraints remain, the main one being the training of farmers in insect scouting and identification. They may account for the small acreage currently sprayed within the context of threshold-based pest control in cotton. (Résumé d'auteur