EVOLUTIONS OF A BLACK-GRASS POPULATION SUBMITTED TO DIVERSE CROP SYSTEMS

Black-grass is a common grass weed, widely spread in Northern Europe and also in Belgium. The first case of resistance in Belgium was reported by Eelen et al. (1996). Since then, monitoring showed that resistant black-grass was not confined to restricted areas anymore and that all usually effective modes of action could be subject to resistance issue (Henriet and Maréchal, 2009). There is no report that agrochemical companies will soon bring a new mode of action effective against grasses on the market, in a close future. It is therefore important to preserve the still effective actives by integrating them into global weeding strategies. A long-lasting trial was set up in order to study the evolution of a black-grass population when submitted to diverse crop systems. Several factors were studied such as rotation (quadri-annual-bisannual-monoculture winter wheat), sowing date (standard date or delayed), cultivation (inversion tillage or not) and herbicide treatments. During three years, each time winter wheat occurred in the rotation, each plot gets the same factorial combination (rotation excepted). In untreated plots, black-grass head counting's showed no differences between tillage or not and bisannual or quadri-annual rotation. On the other hand, number of black-grass heads was higher in standard sowing date and monoculture than in delayed sowing date and other rotations, respectively. The general efficacy of the herbicide treatments was decreasing over the years.