Effectiveness of forage and food legumes on management of the fall armyworm and crop performance in Uganda

Abstract

Maize production in Uganda is constrained by field insect pests, and declining soil fertility. The outbreak of fall armyworm (FAW) in 2016 increased production problems. Increased use of synthetic pesticides and large crop monocultures escalate pest problems and decline in soil fertility. Forage legumes, Desmodium species, in particular have shown capacity to reduce Lepidopteran pest damage in maize as well as improve soil fertility. This study, conducted at Makerere University Research Institute Kabanyolo (MUARIK), set out to compare the effect of food legumes vs. the desmodium forage legume in management of FAW and on soil properties in three consecutive seasons: 2019B, 2020B and 2021A. The treatments included i) maize+soybean, ii) maize+beans, iii) maize+cowpea, iv) maize+green gram, v) maize+desmodium, and vi) maize monocrop. Individual legume monocrops were included to enable calculations of land equivalent ratios (LERs). A randomized complete block design with three replications was used. Data was collected on fall armyworm incidence and damage on maize, plant parameters, crop yield, LERs (calculated), and soil nutrient analysis was done before planting and at harvesting of maize. Results showed that the forage legume and food legumes significantly reduced fall armyworm damage on maize in all the three seasons at P<0.05 and increased levels of available nitrate N and available phosphorous. Generally, food legumes, especially cowpea, beans and soybean did as well as desmodium in reducing FAW larval damage (table 1). The highest pest infestation (36% and 13%) on cobs was under maize planted as sole crop in the seasons of 2020B and 2021A respectively. Though, the yields of the legume intercrops were lower than their corresponding yields as sole crops, LERs are greater than 1 (one) with a higher contribution by maize, indicating a maximum resource utilization and yield advantage of the intercropping system compared to the mono-cropping system. The intercrops of cowpea and beans performed as well as desmodium intercrop with an average LER of 1.7 (table 6). Thus, these food legumes (cowpea and beans) can be intercropped with maize for management of the FAW, soil fertility rejuvenation, and increased land productivity.