Herbicidal resistance management, strategy

Retzinger, E.J. and C.A. Mallory-Smith (1997). Classification of herbicides by site of action for weed resistance management strategies. Weed Technol., 11 384-393. 

Table 11.6 contains results from field trials of atrazine in combination with various ALS-inhibitor herbicides on six ALS-resistant biotypes. This pictorial representation of field data shows the efficacy level of atrazine, ALS-inhibitor herbicides, and atrazine in combination with the ALS herbicide. These trials clearly show the utility and need for atrazine in resistance-management strategies. 

Chemical, cultural, and mechanical weed control practices have been relatively successful ia reducing yield losses from weeds (448). However, herbicide-resistant weed populations, soil erosion, pesticide persistence ia the environment, and other problems associated with technologies used (ca 1993) to control weeds have raised concerns for the long-term efficacy and sustainability of herbicide-dependent crop production practices (449). These concerns, coupled with ever-increasing demands for food and fiber, contribute to the need for innovative weed management strategies (450). 

Kemp, M.S., S.R. Moss, and T.H. Thomas (1990). Herbicide resistance in Alopecurus myosuroides, pp. 376-393. In Green, M.B., H.M. LeBaron, and W.K. Moberg, eds., Managing Resistance to Agrochemicals From Fundamental Research to Practical Strategies. Washington, DC American Chemical Society Symposium Series 421. 

For example, kochia is normally very sensitive to atrazine and can often be controlled with l.lkg/ha (llb/A) along railroads and on farm lands. However, Burnside et al. (1979) reported that after 13 years of atrazine use, Union Pacific personnel were applying up to 15 kg/ha (13 lb/A) with poor control. These high rates are no longer allowed for atrazine uses. The use of mixtures of triazines and herbicides with alternate modes of action has been an effective management strategy to control weeds resistant to triazines. 

Modem herbicides have revolutionized the efficient production of most agricultural crops, and they will continue to be essential in feeding our present and future population. Atrazine and the triazine herbicides are critical in the management of weeds resistant to alternative herbicides. We must continue to develop management strategies for triazines and other herbicides as essential tools for weed control in agricultural production. 

Herbicides comprise 60-70 percent of total usage of pesticides in developed countries. Plants develop resistance to herbicides which in turn demands altered management strategies through improved herbicides and/or herbicide mixtures. This may involve different modes of action, for short-term efficacy and long-term control to be effective. 

One might imagine the extensive development of herbicide resistance in weeds would have led to the development of new tools or agronomic practices to deal with the problem. Unfortunately, this is not the case. A variety of new approaches to weed control can be imagined, but in only a few cases has this translated into practical solutions that can be used to manage the problem in farmers fields. Some strategies proposed many years ago remain theoretical, with no clear examples to demonstrate practical utility. 

Past experience has shown that weeds resistant to triazines can be managed or confined within a reasonable limit. In the U.S., the total area of land or crops infested with triazine resistant weeds is still relatively small and does not seem to be expanding rapidly. In most areas of the U.S. where triazine resistant weed populations have evolved, it has not been necessary or desirable to discontinue the use of the triazine herbicide of choice, due to the many triazine susceptible weeds that are usually prevalent. In a few cases, the resistant biotypes have even disappeared (e.g., some triazine resistant biotypes of Setaria sp. in Nebraska). However, in other countries, especially when resistance strategies were not followed, resistant biotypes quickly became serious problems. 

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