Long-term and large-scale field tests with different weed control methods and agricultural vegetation surveys provide an appropriate tool for an evaluation of the effects on biodiversity of different weed control strategies. In this paper, the toxicological effects, amounts and frequencies of applications, and changes in farming practice are described and compared. The test results are discussed in relation to the question of whether environmental benefits can be achieved by the herbicide-resistance technique. Cropping history and the absence of beneficial plant species invading from the vicinity often override the effects of actual farming practice. Thus long-term strategies are necessary in order to increase biodiversity.