Management of stem borers using selected botanical pesticides in a maize-bean cropping system

Sustainable maize production in sub-Sahara Africa causing 20-80% grain yield losses. Although effective synthetic pesticides are available, the smallholder farmers are yet to fully integrate them in their crop production practices hence the need for scientific rationalization of indigenous pest management options. Aqueous extracts (0, 0.85 and 1.70% w/v) and crude powders (0, 15 and 30 kg/ha) of three botanicals, Lantana camara L., Tephrosia vogelii Hook, Tagetes minuta L. were evaluated for efficacy against stem borers and their effects on productivity of a maize-bean intercrop. Field experiments were laid out in a randomized complete block design (RCBD) with three replicates per site. Results from the field bioassay trials showed that application of crude powders of T. vogelii, T. minuta and general plant ash at 15-30 kg/ha reduced (P<0.005) the stem borer population by 18-63% and increased (P<0.05) the maize grain yields by 30-70% (1.971-2.577 ton/ha) compared to the untreated control (1.534 ton/ha). Irrespective of site, season or cropping system, the application of botanical crude powders and general ash, at 30 kg/ha, were as effective as the synthetic insecticide, Stalk borer™ 2% dust, applied at 10 kg/ha. The powder treatments, at 15-30 kg/ha, increased the bean yield by 98-260% (av. 150%) in the intercrop plots compared to untreated control. Similar result trends on stem borer population and maize and bean yields were observed for aqueous botanical extracts applied as seed-soaking and sprays treatments. The choice of botanical plant to use against stem borers in maize-based cropping is largely governed by the availability and ease of agronomic manipulation by target users. The results of this study are discussed in the context of their relevance, acceptability, economic viability and suitability as good agricultural practices consistent with food security and wealth creation strategies in smallholder agriculture. Key words: Lantana camara, Tagetes minuta, Tephrosia vogelii, stem borer, botanical pesticide