Effectiveness of soil-applied herbicides with mechanical weed control for conservation tillage systems in soybean

Producers who adopt conservation tillage systems need information on effective weed control strategies, In 1991 and 1992, various weed control strategies were evaluated in soybean [Glycine max (L.) Merr.] grown with three tillage systems at two locations in southern Ontario. Primary tillage treatments were fall moldboard plowing (MB), fall chisel plowing (CP), and first-year no-till (NT), Combinations of mechanical weeding, residual herbicides broadcast at two rates, and a band application of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) plus linuron (N'-(3,4-dichlorophenyl)-N-methoxy-N-methylurea were investigated as treatments within each tillage system, Timely rotary hoeing reduced weed numbers in MB and CP treatments, but was not effective in NT. In general, weeds were controlled by residual herbicide plus mechanical treatments (one pass with rotary hoe and two interrow cultivations) regardless of tillage system, or whether herbicides were applied in a band, or broadcast at either reduced or full rates. Herbicides broadcast at reduced rates with no subsequent mechanical weeding controlled weeds in NT; the degree of weed control was inconsistent with location with this weed treatment in MB and CP systems. In general, tillage did not appear to influence the relative proportion of one annual broadleaf weed species over another, However, overall weed populations were lower in first-year NT than MB or CP tillage systems, Annual broadleaf weeds were effectively managed with reduced herbicide inputs in newly established conservation tillage systems.