Effect of pre- and post-emergence herbicides on weed flora and yield of irrigated soybean

Abstract:

\Can herbicide combinations offer a more reliable path to managing complex weed flora in irrigated soybean than single-mode applications? This research was carried out during kharif 2022 at Acharya NG Ranga Agricultural University, Tirupati, Andhra Pradesh, to assess pre- and post-emergence herbicides against diverse weed species in irrigated soybean (Glycine max L. Merrill). Seven treatments were tested in a randomized block design with three replications. The weed flora comprised 14 species including 7 broadleaf weeds, 4 grasses, and 3 sedges. Sequential application of pendimethalin (1.0 kg ha⁻¹) followed by imazethapyr (75 g ha⁻¹) recorded the lowest weed density (20.3 plants m⁻²) and dry weight (17.8 g m⁻²) at 60 DAS compared to the weedy check (98.9 plants m⁻² and 84.6 g m⁻²). Grain yield was highest under the sequential treatment (2.37 t ha⁻¹), statistically at par with hand weeding (2.29 t ha⁻¹) but markedly superior to single herbicide applications and the unweeded control (0.94 t ha⁻¹). The results confirm that integrated pre- and post-emergence herbicide programs can effectively replace labour-intensive hand weeding.