Genes that confer resistance to most major classes of herbicides have been identified by academic and industry research teams, and are being introduced incrementally into major field crops, and especially corn, soybeans and cotton. A few notable, newly developed products are discussed below.
The glufosinate (brand name Liberty) resistance Liberty 280 SL herbicide label allowing post-emergent use on genetically engineered, herbicide resistant (GE-HR) crops in April 2016.is already prevalent and expanding in Liberty Link cotton and soybeans. The approved the
But the major, new GE-HRexpected to dramatically alter the herbicide market in the next five to 10 years are resistance to dicamba and 2,4-dichlorophenoxyacetic acid (2,4-D).
Both 2,4-D and dicamba have been widely used for years, as shown in Figure 3B.1 below. Both are relatively high-risk herbicides just recently approved for post-emergence applications on GE-HR crops. These two herbicides will account for most of the growth in overall corn and soybean herbicide use in the next decade, as clear in the trend tables that follow later in this section.
The EPA approved a registration limited to corn and soybeans in six states for Enlist Duo in 2014, a Dow AgroSciences herbicide containing the choline salt of 2,4-D (24.4% of the original Enlist Duo label was stamped “Approved” by EPA on March 31, 2015. An updated, amended label was approved by EPA on January 12, 2017 that authorizes applications in 25 additional states.product), glyphosate (22.1%), and various unnamed adjuvants and surfactants (53.5%). The
Three post-emergence labels for dicamba have now been granted. The Monsanto dicamba formulation, called XtendiMax, contains the diglycolamine (DGA) salt of dicamba. The XtendiMax label was approved by EPA on November 9, 2016. A similar herbicide, FeXapan, is manufactured by DuPont and won EPA approval on July 23, 2015.
BASF has registered Engenia, the N,N-bis-(3-aminopropyl) methylamine (BAPMA) salt formulation of dicamba. The Engenia supplemental label was approved by EPA on December 20, 2016. This BASF herbicide likely has the most effective combination of technologies designed to reduce dicamba volatilization and drift, and hence off-target crop damage.
The dicamba resistance trait was developed by the University of Nebraska in 2005. At that time, Monsanto was still downplaying the potential for glyphosate-resistant weeds to pose significant or new weed management challenges (Dill, 2005).
The company now projects that dicamba-resistant soybean seed sales in the US will account for about two-thirds of national soybean acreage by 2020. This market has been created by the need to manage glyphosate-resistant weeds.
Remarkably, Brett Begemann, Monsanto’s President and COO, announced in a 2016 “Whistle Stop Tour” presentation to investors that the company would eventually convert its global, ~350 million acre GE-HR Roundup Ready platform to Roundup Ready Xtend (i.e., dual glyphosate- and dicamba-HR varieties).
He projected that dicamba would soon become the world’s second largest selling herbicide, behind glyphosate.
History of Next-Gen Crops
Next-generation GE, herbicide-resistant crops have been engineered to withstand post-emergence, over-the-crop applications of various combinations of glyphosate, 2,4-D, dicamba, and glufosinate.
Glyphosate, aka Roundup, is the most heavily applied pesticide in history both in the U.S. and globally, and came on the market in 1974. The critical commercial and regulatory decisions required to usher in modern-day GE, “Roundup Ready” crops were reached in the 1980s and 1990s, well before the first GE-RR crop was planted in 1996.
Despite explosive growth in glyphosate use since 1996, there have been no important changes in in 20 years in EPA-set human exposure thresholds, or in the depth and quality of the studies supporting glyphosate uses.
The phenoxy herbicides 2,4-D and dicamba were introduced as commercial herbicides even earlier – in the mid-1940s. Their use rose for over 30 years into the early 1980s, but problems caused by drift and damage to non-target plants, trees, and vines led to efforts to curtail use. Overall use trended downward for many years, but now is rising fast because of the spread of glyphosate-resistant weeds. The key regulatory thresholds governing human exposures to these herbicides in 2017 were also set by EPA decades ago.
Glufosinate herbicides came on the market in the early 1990s, and have a markedly newer toxicological database. Use of glufosinate is increasing now, since it still controls many weeds resistant to glyphosate and other herbicides.
For a detailed look at the history of herbicide use on GE crops, see the cutting-edge Herbicide Timelines we are developing.
Impacts of Next-Gen GE-HR Crops on Herbicide Use
It is possible to project with reasonable accuracy the impact of new 2,4-D and dicamba HR crops on herbicide use because of a unique feature of the market for GE-HR technology.
Adoption and use in 2017, or any future year, will not be driven by demand from farmers, but instead is dictated by the companies via decisions they made in 2016.
The GE-HR traits in corn and soybean seed sold in 2017 reflect decisions made by the companies in 2016 regarding the volumes of different seed varieties they would grow and offer for sale in 2017.
Farmers cannot request that a GE trait be removed from a bag of seed before taking delivery.
Only a small percentage of commercial corn and soybean seed lacks any GE-HR traits, and this supply is quickly exhausted in many regions, especially for new varieties containing other desirable traits, like enhanced resistant to fungal pathogens.
Several months in advance of the fall-winter seed sale season, companies publicly announce the percentage of their commercial corn and soybean seed that will contain various combinations of new and old traits. Since farmers pay a significant premium for each GE-HR trait (usually $7.00 to $15.00 per trait per acre of seed), most farmers choose to take advantage of the traits they pay for, even if they would prefer to purchase seed with fewer, or no GE-HR traits.
In addition to announcing the percentage of the corn and soybean seed supply that will contain various GE-HR traits, the companies also provide detailed documentation to theand EPA regarding the average rates of herbicide application they expect farmers to apply, as well as how many applications are likely to be made in a growing season.
With these key parameters, it is easy to estimate “rates per crop year” (average one-time rate of application multiplied by the average number of applications). Plus, herbicide product labels also specify maximum, allowed annual application rates, which sets an upper limit on legal applications per acre.
Herbicide Use on Dicamba and 2,4-D Resistant Crops
Farmers planting dicamba-resistant soybeans can apply up to 2.0 pounds of dicamba(a.i.) in a crop year via four applications, each containing up to 0.5 pound of a.i. (see the labels cited above).
If an average 1.25 pound/acre of dicamba is applied, dicamba use on soybeans would rise from ~180,000 pounds a.i. in 2015 to ~69 million in 2020, as shown in Table 3B.1 below.
On corn and soybeans engineered to resist applications of 2,4-D, farmers will be allowed to apply up to 1.9 (corn) and 2.85 (soybeans) pounds of a.i. per acre respectively, as this EnList Duo label shows.
In corn, Dow AgroSciences projects that ~40 million acres will be planted to 2,4-D HR seeds in 2020, and these acres will be treated with 1.16 pounds of 2,4-D active ingredient (a.i.) over the crop year (see Table 3B.2). Use of 2,4-D on corn would rise from ~3 million pounds a.i. in 2011 to ~21 million 2017, and to ~50 million by 2020.
Soybean producers will plant an estimated 15 million acres of 2,4-D HR soybeans in 2017 and 38 million in 2020, based on Dow AgroSciences projections (Table 3B.3). The company projects that these acres will be sprayed with an average of 1.35 pounds a.i./acre, increasing 2,4-D use on soybeans from 5.4 million pounds a.i. in 2011 to ~25 in 2017, and ~55 million in 2020.