Effects of grain legumes and cover crops on maize yield and plant damage by Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in the humid forest of southern Cameroon

Field trials were run in the humid forest zone of Cameroon to investigate the effects of crop rotation, cover crops and bush fallow on infestations by the noctuid stemborer Busseola fusca (Fuller) and on yield of maize. A continuous maize production system was compared with crop sequence systems, in which maize followed a grain legume (cowpea, soybean), cover crop (mucuna, pigeon pea) or a bush fallow. Compared to the continuous maize cropping system, maize in the crop sequence with legume and fallow systems had significantly higher leaf and stem nitrogen content at 35 and 63 days after planting (DAP), respectively. Differences in K and P at 35 and 63 DAP, and of N in stem and grain at harvest were not significant. Maize in the rotation systems had 1.5-2 times more borers per plant compared to the continuous maize production systems, particularly at the early stages of maize growth. At 63 DAP, larval mortalities were 1.4-1.5 higher in rotation systems than in the continuous maize system. As a result, dead-hearts and tunnel length did not vary significantly among treatments. In the insecticide protected plots, when comparing with the maize-maize cropping system, average grain yields were increased by 15.1-24.6% and 30.3-42.5% in crop sequences of grain legumes with maize and cover crops fallow systems, respectively. However, grain yield losses due to borers were 1.9-3.1 times higher in the continuous maize production system than in the crop sequences of grain legumes with maize and 4.5-11.1 times higher compared to maize after cover crops. It is concluded that an increased nutritional status of the plants lead to an increase in borer attacks at the early stage of plant growth, but also to improved plant vigour, resulting finally in a net benefit for the plant and grain yield.