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New report finds that herbicide-resistant crops have increased pesticide use

(Wednesday, Oct. 27, 2004 -- CropChoice news) -- The following comes from the conclusions and future prospects section of a new report by Benbrook Consulting Services -- "Genetically Engineered Crops and Pesticide Use in the United States: The First Nine Years".

"While the discovery and adoption of GE crop technology has changed American agriculture in many ways, reducing overall pesticide use is not among them. Bt transgenic crops have reduced overall insecticide use, but HT crops have increased it by a far greater margin. Moreover, the performance of HT crops appears to be slipping.

The average acre planted to glyphosate-tolerant crops is requiring more and more help from other herbicides, a trend with serious environmental and economic implications.

Resistance to glyphosate has emerged as a serious concern across most of the intensively farmed regions of the U.S. The number of resistant weeds and their rate of spread is not surprising given the degree of selection pressure imposed on weed populations by farmers applying glyphosate herbicides multiple times per year, and sometimes year in and year out on the same field.

Resistant weeds typically emerge first on just a few isolated fields, but their pollen, genes, and seeds can travel widely and spread quickly, especially if glyphosate continues to be relied on as heavily has it has been in recent years. This is why both universities and some herbicide manufacturers are calling for more aggressive, prevention-oriented management of resistance to glyphosate. In the case of the weed marestail, the recent focus on resistance management has come too late.

No substantial change in the intensity of glyphosate use in the U.S. is expected in the foreseeable future, given the continued popularity of HT crops dependent on glyphosate, the limited supply of non-HT seed in some popular varieties, and the increasingly aggressive promotions offered to farmers relying exclusively on Roundup Ready technology. As a result, marestail will almost certainly be the first of several glyphosate-resistant weeds that emerge and spread, triggering the need for additional herbicide applications and eroding the cost advantage and popularity of HT technology.

The future of Bt transgenic crops is brighter, especially in the case of Bt cotton. Several university and USDA researchers are closely monitoring efficacy in Bt cotton, which appears to have changed little over the last nine years. The attention focused on resistance management, and the issuance of mandatory resistance management plans, has proven effective thus far in delaying the emergence of resistance. Indeed, some experts now think that the emphasis on resistance management in Bt cotton can be relaxed. History suggests that lessened diligence in cotton insect resistance management efforts would be premature, given that it has taken 10-15 years for cotton insects to develop resistance to each new type of insecticide applied to control them. This cycle began with the organochlorines in the 1960s and 1970s, and then repeated itself with the carbamates in the 1970s and 1980s and the synthetic pyrethroids in the 1980s and 1990s. Prudence dictates waiting until about 2010 before determining whether contemporary resistance management plans are indeed working and might possibly be simplified.

Bt corn for control of ECBs and SWCBs remains highly effective but is also almost certainly overused. Many farmers are planting these varieties as an insurance policy against potentially damaging insect populations. In 2004, Monsanto introduced its new Cry 3Bb Bt corn for rootworm management and by 2005, several corn varieties will express both the Bt toxin targeted toward the ECB/SWCB and the new toxin designed to manage corn rootworms.

There has been virtually no field research or regulatory review of the ecological and food safety implications when widely planted Bt corn varieties are simultaneously expressing dual Bt genes. Current USDA and EPA approvals are based on the assumption that the two Bt transgenes in corn plants will operate exactly as they do in varieties engineered to express a single Bt gene, and that the impacts of the dual transgenes will not in any way be additive or decrease the stability of gene expression. These are significant and questionable assumptions that if incorrect, could lead to major, unintended consequences. For this reason, these assumptions should be subjected to empirical study before widespread planting of dual- Bt varieties is authorized."

The full report is available at http://www.biotech-info.net/technicalpaper7.html