The latest report is by Charles Benbrook, PhD, Chief Scientist, The Organic Center, titled “Impacts of Genetically Engineered Crops on Pesticide Use: The First Thirteen Years.” The basic arguments of the report are that planting of biotech soybeans, corn and cotton has resulted in increased use of pesticides (herbicides and insecticides) and weed resistance has increased from repeated yearly planting of biotech crops. The analysis is mostly based on pesticide use data from the National Agricultural Statistics Service (NASS) of USDA.
According to Benbrook, planting of Bt corn has reduced insecticide use for the thirteen years from 1996 to 2008 by a total of 32.6 million pounds, 0.1 pounds per acre. Insecticide used on cotton declined by 31.6 million pounds, or 0.4 pounds per acre from 1996 to 2008. Herbicides used on herbicide tolerant soybeans, cotton and corn increased 382.6 million pounds over the thirteen years compared to the amount used if there were no biotech crops, with most of the increase, 351.0 million pounds, 0.55 pounds per acre, on soybeans. These are active ingredient pounds and do not account for differences in the Environmental Impact Quotient of pesticides. For the thirteen years, 46 percent of the increased use occurred in 2007 and 2008. Part of the claimed increase in herbicide use is due to incremental reductions in estimates of application rates of herbicides applied on non-biotech crops. These rates are not directly surveyed by NASS and are calculated as residuals after estimating the average amount of herbicides used on biotech crops.
For insect resistant Bt crops Benbrook notes, “Sustaining the efficacy of Bt crops is both important and possible.” Resistance management plans that require some portion of the crop to be planted to non-Bt “refuge” varieties is seen as the key factor in avoiding a buildup of resistance in insects.
Herbicide resistant weeds are not a new problem just associated with biotech crops. According to upper bound estimates reported by Benbrook, in the late 1970s about 1.9 million acres of U.S. cropland had weeds resistant to photosystem II inhibitors, mostly the herbicide atrazine which is still used today. Weed resistance on 9.9 million acres has been observed for the ALS inhibitor herbicides. For 2001-08 about 5.4 million acres were found with weeds resistant to glyphosate. Glyphosate has been low cost, effective and easy to use. It is not a surprise that producers would use it until a more cost effective program becomes available.
Benbrook’s suggestions for dealing with herbicide resistant weeds include altering crop rotations, following herbicide resistance management plans and deep tillage before planting and mechanized cultivation between rows of growing crops. The first two suggestions are not controversial, but the suggestions of more soil tillage is counter to efforts over the last 30 years to reduce tillage to lower production costs and improve soil and water quality. It also runs counter to recent efforts to reduce release of carbon to the atmosphere from the soil and use of fossil fuels.
A May 2009 analysis by Graham Brooks and Peter Barfoot of PG Economics titled “GM Crops: Global Socio-Economic and Environmental Impacts 1996-2007” quantifies the economic and environmental impacts for the U.S. and may explain why producers have adopted biotech crops despite some challenges. Adoption of herbicide tolerant soybeans in the early years reduced production costs in the U.S. by $10-14 per acre and $16-25 per acre in recent years from lower herbicide and fuel costs compared to non-biotech soybeans. Herbicide tolerant corn reduced costs by $8-10 per acres, and herbicide tolerant cotton reduced costs by $1-20 per acre. Insect resistant corn increased yields by 5 percent, while costs went up $1-4 per acre as the technology fee was higher than the reduced insecticide costs of $6 per acre. Rootworm resistance in corn has also increased yields by 5 percent, with technology fees of $14-17 per acre slightly exceeding insecticide savings of $13-15 per acre. Insect resistant cotton increased yields by 9-11 percent and reduced pesticide outlays slightly exceeded the cost of the technology fee.
Graham and Barfoot also note that biotech crops have indirect farm level economic impacts like increased management flexibility, adoption of conservation and no-tillage systems, lower harvesting costs due to weed-free fields, less human insecticide exposure and lower production risks. Estimates for the Midwest for fuel savings in corn production compared to conventional-tillage programs show a 17 percent fuel reduction for mulch-till, 25 percent for ridge-till and 50 percent for no-till. Fuel savings for soybeans compared to conventional-tillage are 8 percent for mulch-till, 25 percent for ridge-till and 75 percent for no-till. Continuous use of no-till can result in an increase of carbon sequestration in the soil.
A recent release from the Weed Science Society of America indicates that progress is being made in adjusting to the reality that glyphosate is not the one application solution to all weed problems. Results after three years of a four year study in six states compare the economics of university-recommended, herbicide resistance management programs with the use of glyphosate as the only weed control. The net returns on fields with best management practices are equal to or greater than returns on those fields where glyphosate is used alone because increased yields appear to offset any increase in herbicide costs.
The debate over biotech crops will not end with one more report from any group. Farmers in the U.S. and around the world will continue to manage weeds and insects using the best management practices available consistent with maintaining yields and controlling costs. Those choices are becoming increasingly complex as producers manage for new condition like carbon sequestration. Biotechnology is an established tool to help manage competing trade-offs.