The impact of glyphosate-tolerant crops on the use of other herbicides and on resistance management

Abstract

Glyphosate can now be used for selective, post-emergence weed control in glyphosate-tolerant varieties of soybeans, cotton, canola and maize. It is estimated that glyphosate-tolerant soybeans in the US will account for 60–80% of the area planted by 2001. The rapid acceptance of this new technology is due to multiple factors including broad-spectrum weed control, low cost and simplicity. The use of glyphosate has resulted in a major reduction in the use of other herbicides including the ACCase inhibitors, ALS inhibitors, and Protox inhibitors. In the short term (three to five years) this change in herbicide use patterns will continue. In the long term (five to eight years), the primary reliance on glyphosate for weed control particularly in continuous cropping or in rotations of glyphosate-tolerant crops will result in a shift in the weed spectrum toward more tolerant weed species. As a result of this shift, other herbicides will be needed to fill these weed gaps. Continuous use of glyphosate may also lead to the selection of glyphosate-resistant weed populations, as has already occurred in Australia. However, shifts in the weed species' composition from highly susceptible toward more tolerant species will happen more rapidly than selection of resistance. New herbicides developed in the future will have to be extremely cost-effective to compete against glyphosate and may be geared towards controlling weeds tolerant to glyphosate. There will also be further development of new tolerant crops to other broad-spectrum, non-selective herbicides that will be able to compete directly with glyphosate. © 2000 Society of Chemical Industry