GM crops increase pesticide use.

• Author: Ching, Lim Li
• Position: Thinking Ecologically

A new report from Dr. Charles Benbrook, director of the Northwest Science and Environmental Policy Center, Idaho, concludes that the 550 million acres of GM corn, soybeans and cotton planted in the US since 1996 have increased pesticide use (herbicides and insecticides) by about 50 million pounds. Benbrook is a respected agricultural economist and was Executive Director of the US National Academy of Sciences Board on Agriculture from 1984 to 1990. The report is the first comprehensive study of the impact of all major commercial GM crops on pesticide use in the US over the first eight years of commercial use, 1996-2003. Most studies to date have only focused on the first three years of GM crop adoption (1996-1998), and no study has estimated impacts in 2002 and 2003.

Benbrook draws on official US Department of Agriculture (USDA) data on pesticide use by crop and state to calculate the overall impact of GM crops on the volume of pesticides applied on corn, soybeans and cotton. These three crops account for nearly all the area planted to GM crops in the US. The analysis focuses on herbicide tolerant (HT) corn, soybeans and cotton; and corn and cotton genetically engineered to produce the natural insecticide Bacillus thuringiensis (Bt).

HT crops allow broad-spectrum herbicides to be sprayed over growing plants, controlling weeds while leaving crops unharmed, making them popular with farmers. Despite increased seed prices, HT systems have become less expensive, largely because the price of herbicides containing glyphosate (Roundup) has fallen by half since HT crops were first introduced. (Crops tolerant to glyphosate, known as Roundup Ready varieties, are the largest share of acreage planted to HT crops).

Soybeans account for about 75% of the 400 million acres of HT crops and 54% of all GM acres that have been planted since 1996. While total pounds of pesticides applied to Bt corn and cotton have fallen modestly, the increase in herbicides applied on HT soybeans has been far greater. This, combined with the dominance of HT soybeans, has led to dramatic change in overall impact of GM crops on pesticide use.

Benbrook calculates the difference between the average pounds of pesticides applied on acres planted to GM crops, compared to the pounds applied to otherwise similar conventional crops. In their first three years of commercial sale (1996-1998), GM crops reduced pesticide use by about 25.4 million pounds, but in the last three years...