Crop cultivars, herbicide tolerance

Chemical herbicides have been available for more than a century but major impacts on crop production awaited the development of "truely" selective herbicides or innovations that would permit use of non-selective herbicides in crop situations. We now have some form of selective chemical weed control for most of our major crops. However, continuing problems with herbicide injury to crops as well as poor control of weeds that are botanically similar to crops remind us that further improvements in herbicide selectivity are still needed. Introductions of new selective herbicides will continue but the high costs of these new chemicals are stimulating efforts to make wider use of existing herbicide chemistry. One successful approach has been to genetically improve the tolerance of new crop cultivars to major herbicides... 

However, ideal levels of crop selectivity are difficult to achieve. Several approaches to supplement natural crop selectivity have been used, including development of chemical safeners that improve herbicide tolerance of corn and sorghum (2), restriction of herbicide use to tolerant cultivars (3), transfer of tolerance to crop cultivars by breeding methods (4), and optimization of the site, timing, and method of herbicide application. 

Classical Approaches to the Development of Herbicide Tolerance in Crop Cultivars... 

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