Influence of Cropping and Irrigation Systems on Population Fluctuation of the African White Rice Stem Borer ( Maliarpha separatella Rag) and Damage on Rice

摘要

Information on the population fluctuation of African white rice stem borer ( Maliarpha separatella Ragonot), which is a major rice pest in Kenya, is not known. Availability of such information can assist in the development of an integrated management strategy for the pest. Therefore, a study was conducted at Mwea irrigation scheme in Central Kenya, to investigate the influence of irrigation water provision and cropping systems on population of M. separatella. Farmer fields in different parts of the scheme were sampled every fortnight. The farms represented three irrigation water provision schedules and three cropping systems regimes. The irrigation water provision schedules were, System of Rice Intensification (SRI), flood irrigated (conventional method) and sporadic irrigation. The cropping systems were main season crop (conventional method), double crop and ratoon. Water provision schedules were treated as main plots, while cropping systems were the sub plots. Results showed that the highest percentage of white heads (13.66) occurred in areas, where rice was double-cropped and where, there was sporadic water provision (9.70). There were no significant differences in the number of white heads (empty panicles) between the on-season (6.37) and ratoon (4.25) cropping system. There were also no differences between flood (4.42) and System for rice intensification (5.48) methods of irrigation. This study demonstrates that irrigation methods and cropping systems greatly influence fluctuation of M. separatella infestation and suggests that in case of double cropping it will be necessary to control the stem borer and efforts should be made to ensure that farmers synchronize planting dates.