Impact of Mechanical and Chemical Weed Control on Yield of Groundnut (Arachis hypogaea L.) var. Nyanda at Rattray Arnold Research Station in Zimbabwe

Abstract

Weed control is a major challenge to smallholder farmers in Zimbabwe. Groundnut (Arachis hypogaea L) is highly susceptible to weed infestation because of its slow growth in the first 40 days after sowing (DAS). Manual weed control is the predominant weed control method among these farmers but it is expensive. A study was carried out at Rattray Arnold Research Station in Zimbabwe during the 2014/15 summer season to evaluate weed control methods that can be adopted by smallholder farmers. The major objective was to evaluate the impact of weed control methods on yield in groundnut and to compare effective herbicides combinations for weed control. The variables measured among others, include pod yield, weed density, phytotoxicity and haulm yield. The experiment was laid out in a randomized complete block design (RCBD) with twelve treatments and three replications. Each plot was 12.60 m2 gross plot size and 7.65 m2 net plot size. Weed control methods evaluated were manual control (farmer practice), chemical control only (pre-emergence Bateleurgold 48 EC and Metolachlor 960 EC; post-emergence Classic 25DF and Agil 10 EC) and an integration of chemical and mechanical control. All weed control treatments significantly (P<0.05) increased groundnut yield and reduced weed density and weed biomass as compared to the unweeded control. Pre-emergence application of Bateleur gold at 1.0l a.i./ha along with one hand weeding at 42 DAS resulted in the best weed control with a significantly (P<0.05) higher pod yield (3685 kg/ha). Pre-emergence application of Bateleur gold along with post-emergence application of Agil achieved a yield of 3649 kg/ha, pre-emergence application of Metolachlor at 1.0l a.i./ha along with post-emergence application of Agil achieved a yield of 3567 kg/ha and pre-emergence application of Metolachlor along with one hand weeding at 42 DAS achieved a yield of 3403 kg/ha. These three treatments were statistically the same with pre-emergence Bateleur gold + hand weeding at 42 DAS. Hand weeding twice at 21 and 42 DAS achieved a yield of 2791kg/ha and the weedy check treatment achieved 980 kg/ha. The un-weeded control treatment had the most weed-infested plots with a total weed density of 59 weeds /m2 and was higher than the Bateleur gold and Agil treatment with weed density of 4 weeds /m2. Results of this work show that it is advantageous to use pre and post-emergence herbicides alone or in combination with hand weeding (42 DAs) to control weeds in groundnut. There were no significant differences among shelling percent and 100- kernel weight. Maximum net return was obtained from Bateleur gold + hand hoeing at 42 DAS (US$1749.00) treatment. This was followed by Bateleur gold + Agil (US$1746.40) and Metolachlor + Agil treatments with US$1705.20. However, highest benefit cost was obtained from Metolachlor + Agil (US$103.00) and this was followed by Bateleur gold + Agil (US$69.60). Chemical weed control is a better method than mechanical and forms an integral part of the modern groundnut production cultivation.