Oilseed rape mechanical weed control as an alternative or a complement to chemical weed control

摘要

For agronomic, economic and environmental reasons, weed control in farming systems can no longer only rely on selective herbicides. In this context, mechanical weed control can be an alternative or a complement to herbicides. Trying to reduce the production costs and solving weeding problems that herbicides cannot solve are the two main reasons that lead farmers to adopt these techniques, but they also express fears about the high sensitivity to the climate and the work time these techniques require. Three tools have been tested in a network of 15 farmers' fields since 2003, alone or combined with herbicides: the in-row hoe, the finger weeder and the rotary hoe, in different types of soils and on different weeds. The selectivity has been assessed for each tool:the in-row hoe can be used from stage 3 leaves of the oilseed rape until the moment when the oilseed rape covers the inter-row;the finger weeder at pre-emergence stage and then from stage 3 leaves; the rotary hoe from pre-emergence to stage 4-5 leaves,including cotyledon stage. The efficacy of the finger weeder and the rotary hoe are very dependant on the development stage of the weeds: it strongly decreases when the weeds have more than 3 leaves. Efficacy rates of 80% and more have been reached in the trials in optimal conditions (weeds stage, soils, climate, etc...). Mechanical weed control is efficient against weeds that are hard to destroy with herbicides (crucifer weeds for example). One technique consists in spraying herbicides only on the row when sowing, and then using the in-row hoe to destroy weeds between the rows. The quantity of herbicides is thus reduced by 60% since only a part of the surface is treated. In-row hoeing without any herbicides is usually not efficient enough. Decision grids have been built to guide farmers in the use of these tools, according to the stage of the crop and the weeds, the soil humidity etc...An economic assessment has been made, that shows that mechanical weed control can be profitable thanks to the saving in herbicides costs, but the profitability of these techniques is very dependant on the number of hectares on which they are used.