Impact of changed cropping practices on weed occurrence in spring cereals in Finland - a comparison of surveys in 1997-1999 and 2007-2009.

S alonen J, H yvönen T, K aseva J & J alli H (2012). Impact of changed cropping practices on weed occurrence in spring cereals in Finland - a comparison of surveys in 1997-1999 and 2007-2009. Weed Research. Summary During recent decades, arable cropping has been intensified to increase production, but has also been constrained by agri-environment schemes. Weed populations respond to such changes, thus indicating trends in cropping practices. In Finland, repeated monitoring of the weed flora aims to record and understand the response of weed populations to changing cultural conditions. Two recent surveys of the weed flora in Finnish spring cereal fields, conducted in 1997-1999 and 2007-2009, were evaluated to assess the effect of known changes in tillage practices and herbicide use on weed occurrence. The same 382 fields were assessed during both decades. In conventional cropping, the total abundance of weeds has remained at about the same level as recorded in the late 1990s. Overwintering weed species like Galium spurium, Lamium spp., Lapsana communis and Poa annua have become more frequent, indicating a trend towards reduced primary tillage. Increased use of glyphosate has in turn led to a decline in Elymus repens, particularly in non-ploughed fields. Substantially increased total biomass of weeds was associated with organic cropping, due to lack of direct weed control methods and inadequate crop competition. The opposite trend was apparent in the fields, which had returned from organic farming back to conventional cropping. The results suggest that more decisive IPM strategies are required, both in organic cropping to stop the increasing weed biomass and in conventional cropping to reduce current reliance on herbicides. [ABSTRACT FROM AUTHOR]