Type and time of autumn tillage with and without herbicides at reduced rates in southern Sweden: 1.: Yields and weed quantity

Environmental as well as economic incentives support the use of integrated weed management (IWM) systems for crop production. In order to reduce the input of agrochemicals for weed control, it may be possible to combine reduced doses of herbicides with appropriate tillage strategies and still maintain acceptable weed population levels. The purpose of this study was to compare the efficiency of different tillage strategies, with and without herbicides at 50% of normal rates, on weed populations and crop yields. The influences of type and time of stubble cultivation, harrowing and mouldboard ploughing were followed in eight long-ten field trials in southern Sweden from 1988 until the spring of 1994. The crop rotations were dominated by spring-sown oats (Avena sativa L,) and barley (Hordeum, distichon L,), Although significant site-by-year-by-treatment interactions were found, certain trends in influences of tillage on weeds and yields were identified. Weed density and weight often decreased in the order: stubble cultivation without ploughing > solely ploughing > stubble cultivation succeeded by ploughing. Grain yields of oats and barley varied 6-50% among tillage systems and the highest yields were often obtained in plots where ploughing succeeded stubble cultivation. Effects of tillage on weeds or yields were usually not influenced by herbicide application. Although only subnormal herbicide rates were used, weed density and weight were mostly reduced by 70-90%, while yields increased by 10-20%. In the spring of 1994, 1 year after the last herbicide application, densities of annual broad-leaved weeds were 40-65% lower in plots previously treated by herbicides than in non-treated plots, and differences among tillage systems were still significant. This study shows the advantage of combining herbicides at reduced rates with stubble cultivation and ploughing. (C) 1999 Elsevier Science B.V. All rights reserved.