World-wide, resistance of pests, diseases and weeds against pesticide use is a growing problem. Weed resistance against herbicides is associated with high selection pressure imposed by the high frequency of application. So far, little attention has been given to economic aspects when designing resistance management strategies. In this article, weed resistance to herbicides is investigated by applying a resource economic framework. Weed sensitivity to herbicide use is considered a non-renewable resource. The optimal path of resource depletion is determined by the initial size of the resource stock, the price of alternative technologies and the social discount rate. The case of weed resistance against atrazine in maize production in Germany is used to assess the costs of the resistance build-up. Until its ban in 1991, atrazine was the dominant herbicide in maize. Panel data of the period 1987-1993 are used to model the process of resistance build-up. It is shown that herbicide treatment costs were rising in fields where maize had a high share in the crop rotation. The higher is the application frequency of atrazine, the higher are the total costs of the resistance build-up. However, the present value of the resource stock depends on the social discount rate for which a range of values is assumed. At a low social discount rate, costs of resistance against atrazine are considerably high, compared to the total value of the land. Ignoring the costs of the resistance build-up leads to an overestimation of the social costs of the atrazine ban. Implications for weed resistance management strategies are discussed with special emphasis on the role of externalities, uncertainty and limited information. It is unlikely that policy measures aiming at provision of information alone will lead to efficient resource use.
