Managing Herbicide Resistance: The Role of Extension

The rapid evolution of herbicide resistance poses a significant threat for conventional agricultural practices. In practice, herbicide resistance seems to be a very complicated problem to deal with. Extension can play a significant role in managing herbicide resistance educating farmers on the main advantages and disadvantages of the available methods aiming to control and minimize herbicide resistance. This could be achieved by redirecting the educational efforts more towards the principles of weed biology and integrated weed management, teaching farmers how to learn, paying attention to the basic prerequisites for the new control methods and providing precise information about the economic usefulness of each proposed method. Introduction The occurrence of herbicide-resistant weeds has become a common and almost worldwide phenomenon, particularly the last few years, due to the continuous use of herbicides as the main method of weed control, in combination with monoculture cropping systems (Shaner, 1995). Such cropping systems, developed since the discovery of selective herbicides, rely mainly on high efficacy and cost effectiveness of herbicides for maximum crop productivity and intensive use of land. However, the strong selection pressure imposed to weed populations by the continuous use of herbicides has resulted in development of resistance. Herbicide resistance poses a major threat to conventional agricultural practices as, to date, more than 250 weed biotypes in 50 countries have been reported to be resistant to one or more than one herbicide(s) (Heap, 2002). Herbicide resistance is expected to strongly affect weed management strategies in the future (Duke, 1997). How herbicide resistance will ultimately influence agriculture may depend on many factors and may vary considerably with crop and location. It is evident, however, that when resistance has been extensively developed, weed management with certain herbicides becomes inadequate and different herbicides or other methods of weed control should be adopted. This may have a great impact on the agriculture of an area (Peterson, 1999). Farmers, on the other hand, do not seem to rapidly adopt new weed management strategies to delay the development of resistance. On the contrary, they tend to continue with a successful herbicide program until it fails and only when resistance to herbicides fully occurs they adjust their weed management practices accordingly (Pannell and Zilberman, 2001). 1 Research Agronomist, Laboratory of Agronomy, Aristotle University of Thessaloniki 541 24, Thessaloniki, Greece [email protected]