Evaluation of Selected Herbicides for Weed Control in Sorghum [Sorghum Bicolor (L) Moench]

Abstract

Sorghum (Sorghum bicolor L. Moench) is a drought tolerant crop with potential for industrial uses. Despite increase in demand for sorghum for industrial use, the local supply is low with weed management being one of the challenges. Seven herbicides treatments, Lumax (Mesotrine, Metolachlor, Terbuthylazine), Primagram (Atrazine, S-metolachlor), Dual gold (SMetolachlor), Sencor (Metribuzin) 2,4-D (2,4-D amine salt), Maguguma (Atrazine, Smetolachlor) and Auxio (Bromoxnil, Tembotrine) were tested against two controls, no weeding and hand weeding, to evaluate their effects on density and biomass of weed and sorghum (Sorghum bicolor L. Moench) at Egerton University Njoro, Kenya. The herbicide treatments were laid out in a randomized complete block design (RCBD) with three replications. Seeds were planted at the onset of rainy season in each location in plots measuring 2.5 m by 4 m each consisting of six rows of orghum. The study was done in two experiments; the first and second experiments tested the effect of selected herbicides and rate of application of promising herbicides, respectively on weeds and sorghum crop. Pre-emergence herbicides were applied immediately after sowing while post-emergence treatments were applied 30 days after sowing (DAS). Weed density and biomass was determined at 30 and 60 DAS. All the data were then subjected to analysis of variance (ANOVA) using SAS version 8.1 and treatment means were separated using Tukey’s HSD test whenever the herbicide effects were significant (P≤ 0.05). Results showed significant ((P≤ 0.05) differences among the herbicides evaluated. Amongst the seven treatments, Sencor (Metribuzin) and 2,4-D were the most effective herbicides in reducing the weed density by 96% and 90%, respectively compared to when no weeding. In the second experiment, a clear dose-dependent response of weed and sorghum biomass to Sencor and 2,4-D herbicides was observed. Increasing rate of application from 0.75 to 1.125 L/ha for Sencor resulted in ≥90 and >70% reductions in weed density and sorghum biomass, respectively but caused up to 92% increase in weed biomass at 30 DAS. With respect to 2,4- D, increasing rate of application from 1 to 3 L/ha resulted in >90% reduction in weed density and weed biomass and up to 70% increase in sorghum at 60 DAS. The highest sorghum biomass of 4117 kg/ha and 6505 kg/ha were recorded for Sencor at 1.875 L/ha and 2,4-D at 2.5 L/ha, respectively. From these findings, it is recommended that Sencor @1.875 L/ha and 2, 4-D @2.5 L/ha be validated for adoption by smallholder sorghum farmers to ensure effective weed management and contribute to increased sorghum production to meet the increasing industrial demand.