Evaluation of Pre and Post-emergence Herbicides for Weed Management in Soybean (Glycine max)

Abstract

Heavy infestation of weeds with grasses, broad-leaved, and sedges poses a big challenge for soybean production. This crop’s initially slow growth, good sunshine, and intermittent rains during the rainy season further provide a congenial environment for the excessive growth of weeds. Recognising the importance of timely weed management in soybean, this investigation was undertaken to study the effect of pre- and post-emergence herbicides on growth, yield, and weed management in the soybean crop. The experiment was conducted from 2018 at 2020 at Agriculture Research Station, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Buldana (Maharashtra). The experiment was laid out in a randomised block design with ten weed management options (T1: weedy check; T2: weedfree; T3: pendimethalin @ 0.677 kg a.i./ha PE; T4: diclosulam 84% WDG @ 0.026 kg a.i./ha as PE; T5: imazethapyr 10% SL @ 0.075 kg a.i./ha at 21 DAS as PoE; T6: propaquizafop @ 0.050 kg a.i. + imazethapyr @ 0.075 kg a.i./ha at 21 DAS as PoE (RM); T7: propaquizafop 10% EC @ 0.075 kg a.i./ha at 21 DAS as PoE; T8: imazamox @ 0.035 kg a.i + imazethapyr @ 0.035 kg a.i./ha at 21 DAS as PoE (RM); T9: quizolofop ethyl 5% EC @ 0.05 kg a.i. + imazethapyr 10% SL @ 0.075 kg a.i./ha at 21 DAS PoE (tank mix) and T10: imazethapyr 10% SL @ 0.075 kg a.i./ ha at 21 DAS PoE + propaquizafop 10% EC @ 0.075 kg a.i./ha at 35 DAS). The Results showed that preemergence application of diclosulam (0.026 kg a.i./ha) and pendimethalin (0.677 kg a.i./ha) significantly reduced weed density at 30 DAS, with diclosulam showing the lowest weed count (35.56 weeds/m²). At 60 DAS, a sequential post-emergence application of imazethapyr and propaquizafop showed superior control (46.22 weeds/ m²). The weedy check treatment had the highest weed density at all growth stages, culminating 387.56 weeds/m2 at harvest. Effective weed management positively influenced growth and yield parameters of soybean. The weedfree treatment resulted in the highest number of branches (6.73/plant) and pods (22.82/plant), with a seed yield of 7.15 g/plant, which was significantly higher than the weedy check. Among chemical treatments, the post-emergence application of propaquizafop and imazethapyr (0.050 kg and 0.075 kg a.i./ha, respectively) at 21 DAS yielded the highest seed production (2031 kg/ha), close to the weed-free treatment. Economic analysis revealed that the weed-free treatment achieved the highest gross monetary returns (Rs. 80,873/ha). However, the propaquizafop and imazethapyr post-emergence applications had the highest benefit-cost ratio (3.01), demonstrating cost-effectiveness by minimizing weed competition and maximizing economic return. In contrast, the weedy check had the lowest returns and a B: C ratio 1.04. These results suggest that combining imazethapyr and propaquizafop post-emergence is an effective and economical strategy for weed management in soybean production.