The effect of tillage intensity and time of herbicide application on weed communities and populations in maize in central Europe

Soil-conserving cropping systems aim at reducing tillage intensity to decrease soil erosion, leaching of nitrate and pesticides, and production costs. They are, therefore, likely to change the efficiency of weed control and hence weed populations. There is a lack of information on how reduced tillage systems, especially no-tillage (NT), affect the development of weed populations and the efficiency of weed control of maize crops under the humid, temperate climate of large parts of Europe. An experiment was conducted at two sites of the Swiss midlands to investigate the impact of the time of chemical weed control on weed populations in different tillage systems. Pre- and post-emergence herbicides were applied in a conventional tillage (CT) system with a moldboard plough, in a minimum tillage (MT) system with a chisel plough, and in a NT system in a winter wheat (Triticum aestivum L.)-oilseed rape (Brassica napus L.)-winter wheat-maize (Zea mays L.) crop rotation. Crop residues were left on the field and stubble tillage was not carried out. The density of weeds in treatments without herbicide tended to be lower in NT than in MT and CT. An analysis of variance and canonical discriminant analysis (CDA) showed that perennial weeds such as Epilobium spp. L. and Sonchus arvensis L. were related to NT, and annual broad-leaved species were associated with MT and CT. In general, post-emergence weed control was more efficient than pre-emergence weed control regardless of the tillage system. However, NT systems may be adopted successfully when weed control measures are adapted to changing weed populations. (C) 2002 Elsevier Science B.V. All rights reserved.