Integrated management of groundnut rosette disease
Groundnut is an important food, feed and cash crop in sub-Saharan Africa. This crop suffers greatly from a viral disease; groundnut rosette (GRD) vectored by an aphid cause 100% yield loss if it occurs before flowering. Management strategies for the disease include reduction of vector populations using pesticides, cropping practices to delay onset and spread of both vector and the disease and growing groundnut varieties resistant to the virus and the vector. The objective of this study was to assess the effectiveness of selected cultural practices, chemical pesticide and host plant resistance in the management of groundnut rosette disease. Field experiments were conducted between March 2007 and February 2008 at Siaya Agricultural Training Centre (Siaya district) and Kenya Agricultural Research Institute, Alupe sub station (Teso district) in Western Kenya. The cultural disease management strategies included alteration of time of planting (early planting at the onset of rains and late planting one month later), host plant resistance, use of trap crops (cowpea and sesame), vector control using a chemical insecticide (dimethoate) and roguing. The experimental design used was randomized complete block laid out as a split-plot and replicated three times. The disease management practices and groundnut varieties were allocated to main plots and subplots respectively. The time of planting significantly influenced aphid population and groundnut rosette disease incidence. High aphid population and GRD incidence was observed in lateplanted than in early-planted groundnut. Late planting reduced groundnut yield by 48- 71%. Application of dimethoate lowered vector population and reduced GRD incidence by 85-94%. Cowpea and sesame trap crops reduced the disease incidence by 56-76% while roguing reduced the disease incidence by 30-44%. Groundnut yield increased by 167-255% where insecticide and trap crops were applied. Planting of varieties resistant to the virus (ICGV-SM 90704) and the vector (ICGV 12991) reduced the disease incidence by 46-61%. Aphis craccivora Koch was the most abundant of the aphid species. This study recommends early planting in addition to combination of host plant resistance with other protective measures such as cultural practices for effective management of groundnut rosette disease. There is however, a need to undertake further studies in order to establish economic injury levels and action thresholds to guide in integrated management of groundnut rosette disease and its vectors.