Enhancing the weed control efficacy of two pre-emergence herbicides in maize/jack bean and maize/groundnut intercrops in derived savanna

The inability of pre-emergence herbicides alone to give season-long weed control in maize production justifies the need for supplementary weed control. Field trials were conducted to evaluate intercropped groundnut and jack bean for enhanced weed control efficacy of two pre-emergence herbicides in maize production in 2013/2014 and 2015 cropping seasons at the Federal University of Agriculture, Abeokuta, Nigeria. The experiment was arranged in split-plot fitted in a randomized complete block design with three replications. Main plots consisted of eight weed control treatments of a commercially formulated mixture of prometryne + metolachlor (ProbabenR); prometryne + acetochlor (Super UnionR) each at 2.4 kg a.i ha-1, 1.6 kg a.i ha-1 with and without supplementary hoe-weeding, two hoe-weedings and a weedy check. Sub-plot treatments consisted of eight cropping patterns (sole maize, maize-jack bean and maize-groundnut intercrops, each at two spacings [100 x 37.5 cm and 75 x 50 cm] and sole crops of jack bean and groundnut). All the weed control methods significantly reduced (p<0.05) weed dry matter compared to the weedy check by 10-81%. Maize grain yields (1.4-5.2 t ha-1) were similar for all plots with the weed control methods, except in the 2015 late season, but significantly depressed (21-48%) on those weed-infested throughout. Intercropped jack bean and groundnut with maize significantly suppressed weed growth relative to sole crops of maize, jack bean or groundnut by 20-67%. Therefore, the efficacy of pre-emergence herbicides in this study was enhanced by intercropping of maize with jack bean and groundnut at the spacings of 75 x 50 cm and 100 x 37.5 cm in the early seasons.