[en] Black-grass is a common grass weed, widely spread in Northern Europe and also in
Belgium. For ages, it has been an increasing problem in industrial crops,
especially winter cereals. Therefore, farmers started to spray herbicide
intensively and soon cases of failure occurred for different molecules and different
modes of action. Black-grass populations have been tested in greenhouses to assess
the influence of an herbicide treatment as to the resistance level regarding three
different herbicides: chlortoluron, fenoxaprop-P and mesosulfuron+iodosulfuron.
Black-grass seeds were collected in field trials in six locations in Belgium, on
individuals which have survived the herbicide treatment. Each population comes from
trial plots, measuring 2 meters wide by 5 meters long and characterized by a single
or a combination of products. Herbicides sprayed were isoproturon,
flufenacet+diflufenican, ACCase inhibitors and ALS inhibitors. Seeds were also
collected in the untreated plots. The population present in these last ones
corresponds to the former population, before the herbicide selection pressure was
applied. In the glasshouse assay, this population was used as the standard
population to compare with other populations issued from the same field. The 'R'
rating system was set up with this population to assess the evolution of resistance
level, year in, year out. Rothamsted and Peldon populations were also included as
cross-reference.
Each field population presented different behaviours towards herbicide applied in
greenhouses and some cases of resistance can be highlighted. Generally, a reduction
of treatment efficiency between field and greenhouse results was clearly visible for
the whole of studied active ingredients. Indeed, a distribution shift of the
populations towards higher resistance classes could be observed. This is
particularly remarkable for active ingredients sharing the same mode of action. For
example, it has been found that populations already sprayed with fenoxaprop-P on the
field showed a higher resistance level to fenoxaprop-P than to mesosulfuron in the
greenhouse test.
