Black-grass resistance to herbicides: three years of monitoring in Belgium.

Black-grass (Alopecurus myosuroides HUDS.) is a common weed of cereal crops widely spread in Northern Europe. Even if the first Belgian case of resistance was reported in 1996, until now, Belgium was quite spared of this problem and only a few restricted areas were concerned: the Polders, the marshland of the Escaut River and the Fosses-la-Ville region. About 90 seed samples were collected trough the South part of Belgium and in the Polders during July 2006, 2007 and 2008. These populations were tested in greenhouse conditions by spraying plantlets with herbicides of three modes of action. The herbicides used were photosynthesis inhibitor, ACCase inhibitors and ALS inhibitors. Susceptible and resistant standard populations (Rothamsted and Peldon) were included in the test in order to validate it and to permit wild populations classification according to "R" rating system. Populations showed differences of susceptibility to photosynthesis inhibitor, ACCase inhibitors and ALS inhibitors. For each herbicide mode of action, it was possible to find at least one population in each resistance class of the "R" rating system. Furthermore, it appeared that resistance was not confined to restricted areas listed above anymore.