A Study of the African White Rice Stem Borer (Maliarpha separatella Rag.) Population Density Fluctuations at Mwea Irrigation Scheme in Central Kenya

Kega, V M,Olubayo F,Kasina, M,Nderitu, J H

doi:10.13189/ujar.2017.050108

Abstract

The African white rice stem borer (Maliarpha separatella Ragonot) is a major pest of rice in Kenya. To understand and develop appropriate management packages, its population dynamics were studied at Mwea irrigation scheme in Central Kenya. This was for two wet and two dry periods. Farmer fields located in different parts of the scheme and outside the scheme were sampled every fortnight. Farms sampled represented five water provision schedules (System of Rice intensification (SRI), rain fed, flood irrigated, sporadic irrigation, and fallow period). Five planting regimes (on season, off season double cropping, ratoon, and late planting) and three management styles (controlled by National Irrigation Board (N.I.B), not controlled by N.I.B and out-growers) were studied. During each sampling, a 1mx1m quadrant was used randomly and pest counted on all the plants within the quadrant. Results showed that the number of M. separatella varied significantly (p<0.05) in the scheme. Pest densities were highest in off season planted rice (13.1). High numbers were also found in Non N.I.B controlled fields with sporadic irrigation (8.1) and the lowest in the N.I.B, fallow (2.5) and this was significant (p<0.05). There were no significant differences in pest infestations on the normal season crop (0.3) and the ratoon crop (0.6) p<0.05 and SRI and conventional irrigated fields (p<0.05). From the results it is recommended that off season planting of rice be discouraged and that efforts are made to ensure that farmers synchronize planting dates and other cultural practices for the crop, within the scheme and in rice farms outside the scheme.

Highlights

Rice is one of the most important food crops in the fight against hunger
The highest pest population numbers was in Non N.I.B controlled fields with sporadic irrigation and lowest in the N.I.B controlled, flood irrigated with fallow period and this was significant (p
The high pest population numbers in Non N.I.B controlled fields with sporadic irrigation is consistent with reports from Litsinger et al 2009 who found that rain fed wetland rice system which may be equated with sporadic irrigation at Mwea was more prone to physiological stresses than flood irrigated crop and this minimizes crop compensation and accentuates losses [10]

Summary

Introduction

Rice is one of the most important food crops in the fight against hunger. The total annual production stands at 400 million MT of milled rice [12], it is the most rapidly growing food source in Africa. Reports indicate that the African white rice stem borer, Maliapha separatella Rag. is a major rice pest in sub Saharan Africa and islands of Comoros and Madagascar [2],[8]. It is the major species in the major upland rice growing areas of West Africa [1],[14], but in East Africa it is important in lowland irrigated rice. Crop loss yield estimates from Kenya varied from 7-34% [5], [6]. This was mainly on late planted crop and on the ratoon in the irrigation schemes at Mwea in Central Kenya and Ahero in Nyanza [5], [6] and [15]

Methods

Results

Conclusion