Introduction
The current demand for reducing herbicide use because of herbicide resistance and environmental concerns has emerged an increasing interest in site specific weed management technologies like patch spraying and robotic weeding. The technological state-of-art of spray techniques, DGPS (Differential Global Positioning System), GIS (Geographical Information System), computer vision and robotics facilitate highly accurate weed mapping and target control of weed patches or even individual weed seedlings.

Treatment maps based on weed maps	Patch spraying with treatment maps
Potential savings A summary of the potential savings of from 59 trials in several countries in Europe is shown in Table 1. The returned field reports showed great differences in designs and methods. Is also showed significant differences in the potential savings between the trials and the crop species. There is no definitive conclusion regarding the differences, but it seems that the goal of weed management, the weed and crop species and the used spray technology have a great influence on the potential savings. The greatest potential seems to be present in fields with sparsely or immigrating weed species. The opposite seems to be the case in with very competitive or homogenously distributed weed species.	Table 1. Potential savings of herbicides in percentage of common practise in 59 trials with site specific weed management in Europe
	Weed sensing and robotic weeding The main obstacle for the progress of site specific weed control is the lack of automated detection and classification of crop and weeds. A new concept is to use historical information about weed distribution in combination with computer vision for identification crop and weed seedlings and highly accurate devices for mechanical and chemical targeting of weed seedlings.

The state-of-art of sensors, GPS/GIS hard- and software and some implements (mainly sprayers) are in advance of the agronomic and biological exploitation of site specific weed monitoring and management. Thus, there is a need for a forum, where weed scientists can discuss and exchange experience and results, and support further progress on site specific weed management - the working group of site specific weed management under European Research Society is such a forum. Svend Christensen (working group chairman)