Tuesday Talks With Dr. Patterson

September 23, 2014

Last week, the USDA approved a new seed technology for corn and soybeans developed by Dow AgroSciences, which makes these crops resistant to the herbicide 2, 4-D (2,4-Dichlorophenoxyacetic acid). This is the latest offering of an herbicide resistant (hr) or herbicide tolerant (ht) crop variety. These crops are genetically engineered to be tolerant or resistant to the effects of specific herbicides. Once growing, the crops can be sprayed by the herbicide to control weeds, thereby killing the weeds without harming the crops. Dow’s new product line, named Enlist, is being brought to market to address the growing problem of herbicide resistant weeds. While the crops were genetically engineered to resist the effects of herbicides, weeds have evolved to also be resistant to the herbicide. The primary resistance is to glyphosate or Monsanto’s Roundup. Approval of Dow’s companion herbicide containing 2, 4-D and glyphosate, named Enlist Duo, must be obtained from the Environmental Protection Agency. The USDA’s approval only signifies that growing these crops will not pose a threat to other agricultural plant or animal species. The EPA will insure the safety of the herbicide and seed for the environment and human health.

Herbicide resistant crop varieties, principally Monsanto’s Roundup ready crop varieties, were introduced in the mid-1990s and their adoption was rapid and widespread. By 2000, 54% of U.S. soybean acreage was planted with hr varieties; by 2014, 94% was in hr varieties (USDA). The herbicide tolerant trait was also introduced in corn and cotton. The crop resistance to glyphosate proved to be a great tool for U.S. farmers. The technology allowed farmers more flexibility in managing weed pests; it helped improve yields and reduced the use of other types of herbicides; it also promoted the adoption of reduced tillage practices, which reduced soil erosion and improved water quality in rivers and streams (National Research Council). However, the widespread adoption of this technology and farmers reliance on glyphosate hastened the evolution of weeds that were resistant to this herbicide. Dow estimates that herbicide resistant weeds are now found on 70 million acres in the United States, double the acreage estimated in 2009 (Enoch). In Alabama, three weeds are now recognized as resistant to glyphosate—Palmer Amaranth, Horseweed, and Common Ragweed (Heap). The presence of these resistant weeds has forced farmers to increase the use of conventional tillage and other herbicides, and, in some cases, resort to hand cultivation—hoeing. So the need for new technologies is obvious. Monsanto is also working on a new product line, which will introduce crop plant resistance to another herbicide, dicamba.

These product developments, while attractive and sought after by farmers, are not without critics. The Center for Food Safety has been a vocal opponent saying that it will result in increased use of herbicides on U.S. cropland. Indeed, the USDA has estimated that use of 2, 4-D will increase by 200 to 600 percent by the year 2020 (Enoch). In public statements last week, the Center for Food Safety commented that 2, 4-D was a component of Agent Orange, the defoliant used in
Vietnam, and that it is in a class of herbicides associated with immune system cancers, Parkinson’s disease, endocrine disruption, and reproductive problems (Pollack). However, it should be remembered that 2, 4-D is already approved for use as an herbicide in the United States. In fact, it ranks third in use behind glyphosate and atrazine (Pollack). The Center also ommented that it would only be a matter of time before weeds become resistant to2, 4-D and dicamba (Pollack). Some Midwest fruit and vegetable growers also raised concerns about increased use of 2, 4-D, as it has a tendency to volatilize and drift when it is applied, causing
damage to crops not resistant to it (Pollack). Dow claims to have addressed this concern in the development of Enlist Duo. Furthermore, famers licensed to plant Enlist crops will have to use Enlist Duo and follow certain protocols in its application to reduce any risk to other crops.

Dow hopes to release its Enlist corn and soybean systems for the 2015 planting season after working through the regulatory systems for about two years. However, it has not obtained import approval from large importers, such as China. Recently, the seed company Syngenta was sued by Cargill over its release of the genetically engineered corn variety MIR 162 (Agrisure Viptera) without obtaining import approval by China. China recently rejected U.S. corn shipments where this variety was present, resulting in losses for the grain trader Cargill (Gonzalez).

The availability of several new hr technologies could help forestall the growth of herbicide resistant weeds. However, many weed scientists believe that we will need to be smart in the use of these technologies. These new technologies will need to be used in combination with other herbicides, in rotation with one another, and in combination with conventional tillage to control weeds. This may help limit the evolution of more bad weeds.


Enoch, Daniel. “USDA Approves New Dow Corn and Soybean Traits.” Agri-Pulse, Sept 17, 2014. http://www.agri-pulse.com/USDA-approves-Dow-Enlist-corn-and-soybean-traits-9172014.asp

Gonzalez, Sarah. “Cargill Sues Syngenta Over Corn Trait.” Agri-Pulse, September 12, 2014. http://www.agri-pulse.com/Cargill-sues-Syngenta-over-corn-trait-9122014.asp

Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Accessed September 21, 2014. www.weedscience.org.

National Research Council. The Impact of Genetically Engineered Crops on Farm Sustainability in the United States. Washington, DC: National Academy of Sciences, 2010.

Pollack, Andrew. “Altered to Withstand Herbicide, Corn and Soybeans Gain Approval.” New York Times, September 17, 2014. http://www.nytimes.com/2014/09/18/business/altered-to-withstand-herbicide-corn-and-soybeans-gain-approval.html?_r=0

USDA Economic Research Service. Adoption of Genetically Engineered Crops in the U.S. Accessed September 21, 2014. http://www.ers.usda.gov/data-products/adoption-of-genetically-engineered-crops-in-the-us.aspx#.VB9xv6ko5wE


Dr. Paul Patterson is associate dean for instruction for the College of Agriculture and Professor of Agricultural Economics.