Evaluation of Maize-legume Compatibility and the Management of Fall Armyworm (Spodoptera Frugiperda) in Kenya

Abstract

Smallholder farmers in East Africa generally intercrop maize (Zea mays L.) with grain legumes to intensify cropping, improve soil fertilizer, reduce pests and disease pressure, and control weeds. However, the compatibility of maize with the majority of legume species is only partially understood, particularly with regards to yield-limiting factors that arise from the intra-specific competition. Intra-specific competition between maize and legumes could be alleviated through both the spatial and temporal arrangement of the companion crops. On the other hand, legumes are frequently integrated into push-pull crop arrangements to suppress field pests in maize such as the stalk borer and lately the fall armyworm. However, the push-pull technology predominantly integrates non-food legumes such as desmodium but evidence shows that food legumes are also effective in manipulating the pest habitat. In addition, the use of food and perhaps dual-purpose legumes could be more attractive to farmers in comparison with the use of desmodium. Further, the efficiency of this technology could be improved through the temporal arrangement of maize and legumes, particularly by relaying maize into established legumes, albeit with knowledge limitations. In the context of these knowledge gaps, a study was carried out with two objectives: (1) to evaluate the compatibility of maize with a diverse range of legumes species in both simultaneous and relay intercrop system; and (2) to assess the effect of simultaneous and relay intercropping of maize with different legumes species on the suppression of Fall armyworm (Spodoptera frugiperda) in maize. Field experiments were carried out at the Kenya Agricultural and Livestock Research Organization (KALRO) in Kiboko and the Kabete farm of the University of Nairobi. In each site, two experiments were carried out, and both experiments consisted of nine legume species: common bean (variety Rosecoco), pigeon pea (Kat 80), dolichos lablab (DL1002), groundnut (ICGV 9704), soybean (SB19), green gram (N26), cowpea (M66) and green leaf desmodium, in addition to sole maize as control. In the first experiment, crops of maize and legumes were sown simultaneously while in the second trial maize was relay cropped into xv established legumes. Both experiments were laid out in a randomized complete block design and replicated three times. In the maize-legume compatibility study, measurements included crop growth traits, yield components and intercropping productivity indices while the second objective comprised leaf feeding damage, dead heart incidence, ear damage rating, and the number of pest larvae, as well as yield components. Analysis of variance showed significant differences among treatments (p≤ 0.05) in maize-legume compatibility and fall armyworm infestation. Intercropping maize with pigeon pea, lablab in relay cropping system in Kabete, significantly (p≤ 0.05) increased yield by 35% and 70% respectively whereas in simultaneous cropping system in Kabete, desmodium and beans increased maize stand count at harvest by 17.6% and 18.5%, respectively. At the same site, simultaneous intercropping of cowpea recorded significantly the highest maize stand count at harvest (113 plants per an area of 180m2) than relay cropping system at (89 plants at the same area). Similarly, in Kiboko, simultaneous intercropping of maize with green gram, lablab recorded the highest maize stand count at harvest by 35 and 40 plants respectively more than relay cropping system. In addition to fall armyworm (FAW) infestation data, simultaneous intercropping of maize with cowpea, lablab, bean, and desmodium significantly (P ≤0.05) reduced FAW damage in maize leaf by 46.6, 47.0, 73.0, and 73.1% respectively at both vegetative and flowering stage at the two sites. Relaying maize into established cowpea, lablab, beans and desmodium significantly (P≤0.05) reduced FAW infestation in maize leaf by 65.9, 75.6, 78.0 and 87.8% respectively from vegetative to the flowering stage at both sites. More ever, establishing maize simultaneously with either lablab, green gram, beans and desmodium significantly (P ≤0.05) reduced the number of FAW pest larvae in maize plant by 42.6, 69.6, 70.0, and 87.0% respectively in all physiological stages across the two sites. Similarly, relay establishment of maize into lablab, cowpea, beans, and desmodium significantly (P ≤0.05) reduced the number of FAW pest larvae in maize plant by 62.2, 70.0, 77.8, and 100% respectively in all stages of growth in both sites. In this study, relaying maize into an already xvi established lablab, bean and desmodium reduced FAW infestation or damage on maize plants at nearly all physiological stages compared with other legumes in all the sites. In conclusion, when comparing means of lablab and bean with desmodium, it shows there are no significant differences between those three legumes. Therefore, it is highly recommended to use lablab and bean instead of desmodium in the management of FAW in maize.