Bio-efficacy of Different Rates of Acetachlor and Alachlor for Weed Control in Soybean [(Glycine max (L.) Merrill]

The studies on bio-efficacy of acetachlor and alachlor at different rates for weed control in soybean made during kharif 1996 and 1997 revealed that acetachlor @ 0.9, 1.35, 1.8 and 3.6 kg/ha and a1achlor @ 2.0, 2.5 and 5.0 kg/ha were effective to control Echinochloa crusgalli and the efficacy increased with the increase in the rates of application. The broadleaf weeds were also controlled; however, the efficacy against Commelina communis and Phyllanthus niruri was relatively less. Trifluralin @ 1 kg/ha failed to control Commelina communis and Cyanotis axillaris, while metolachlor @ 1 kg/ha reduced the population of most of the dominant weed species except Rotalla sp. and Phyllanthus niruri. Acetachlor @ 3.6 kg/ha delayed the germination of soybean by 3–4 days and mortality of seedlings was also observed. The other rates of acetachlor and alachlor did not show adverse effects on germination and plant growth. All the herbicidal treatments gave significantly higher seed yield than weedy control. On the basis of two years' mean, the seed yield amongst acetachlortreatments varied from 1347–1417 kg/ha, white it was 1309–1403 kg/ha under alachlor treatments and all these treatments yielded at par with metolachlor (1478 kg/ha) and trifluralin (1391 kg/ha) as against 969 kg/ha in weedy control. The herbicidal treatments produced 35.1–52.2% increased seed yield over weedy control.