Genetically Engineered Crops and Pesticide Use in the United States:
The First Nine Years

Dr. Charles M. Benbrook
Sandpoint Idaho
October 25, 2004

About This Report

This report is the seventh in a series of Technical Papers prepared by Benbrook Consulting Services on the development, costs and benefits, and environmental impacts of genetically engineered (GE) crops in the United States. The full series of Technical Papers has been posted on the website Ag BioTech InfoNet and are accessible at http:/www.biotech-info.net/highlights.html#technical_papers

The analysis in this report relies heavily on the work of the USDA's National Agricultural Statistics Service (NASS). NASS data are consistent over time and across production regions, key attributes for an assessment over several years such as the one reported herein.

Conclusions and Future Prospects

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 herbicide tolerant (HT) crops have increased pesticide use by a far greater margin. Moreover, the performance of HT crops appears to be slipping. The average acre planted to glyphosate-tolerant crops requires 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.