ABSTRACT

Studies were carried out in Amakama, South-Eastern Nigeria, to determine the effectiveness of Azadirachia ind/da A. Juss, .Jairopha curcas L., Monodora myristica (Gaertn) Dunal and Ricinus communis L. seed extracts in the control of stem borers of upland rice. Stem borer species were determined by collecting adult stem borers through sweep net sampling, dissection of rice stems for stem borer larvae, and rearing of pupae to adult before identification. The assessment of level of infestation was done from damage indices. The effect of planting dates on stem borer infestation was investigated in a randomized complete blocks' design experiment involving four upland rice varieties (FARO 11, FARO 43, FARO 46 and FARO 48) planted from April to July. The effects of 2.5%, 5% and 10% of both acetone and aqueous extracts of the test plants and monocrotophos (applied at 400g a.i/ha) in the control of stem borers were also determined. Timing and frequency of application of botanicals wa investigated in a split-plot experiment. Grain yield losses due to non-protection of rice crop at different growth stages were studied, and the effects of pre-infestation and post-infstation applications of botanicals on stem borer  larvae were investigated. The economics of the use of botanicals was determined from results of the experiments. Four stern borer genera, namely, Diopsis species (D. Ihoracica West and D. apicalis Dalm) Sesamia species (S. calamistis Hmps, and S. inferens Walker) Ivialiarpha species (Ail. separatella Rag) and Chilo species (C. zacconius Blesz) were identified in the study area, but Sesa,nia species were the most destnictive in the area. The date of planting experiment revealed that rice planted from third week of April to third week of May significantly (P< 0.05) suffered less damage from stem borers at the critical heading stage and produced significantly higher yields than rice planted at other dates. The acetone and aqueous plant extracts in their different concentrations significantly reduced stem bor damage and increased rice yield (P<zO.05) when compared with the control. Comparatively, monocrotophos was generally better in terms of stem borer control and influencing yield, but the results were not significantly different from those of a number of the plant extracts. A indica and J. curcas extracts performed slightly better than the other two test plants. In terms of frequency of application, two applications of the plant extracts at maximum tillering and early booting or three applications at early tillering, maximum tilleiing and early booting stages of rice significantly performed better than other applications in terms of stem borer control and influencing yield. Pie-infestation and post-infestation applications of the treatments were equally effective but showed that monocrotophos caused more mortality than the plant extracts. Monocrotophos treated plants gave the highest cost-benefit ratio, followed by A. indica, J. curcas and M myrislica or K communis.