Old data, new benefit - weed surveys combined throughout Europe.
The weed management of modern agriculture will continue its change to less intense use of herbicides and more prominent use of alternative measures. For an effective use of this more complex weed control, a better knowledge and understanding of weed ecology and of reactions to management measures is necessary. In many cases, this knowledge is based on regionally or nationally collected data. The derived conclusions can only be extrapolated with caution. It is difficult to extract a general rule from local observations, and sometimes not possible. In principal, the combination of different datasets from different regions and times provides the possibility to overcome this problem, because a larger part of the existing differences is addressed. The knowledge generated in this way is more general.We show how we approached such a data collection of European weed data and provide an overview of the data gathered so far. We discuss some of the arising problems caused by the high heterogeneity of the data and how we handle them. The data collection was conducted within the framework of the working group "Weeds and Biodiversity" of the European Weed Research Society" (EWRS) with the aim to analyse the factors influencing the occurrence of weeds.