2,4-D Makes a Comeback

2,4-D (2, 4 Dichlorophenoxyacetic acid) has long been one of the most widely used herbicides in the world, yet resistance to it barely registers compared to the spreading trouble glyphosate has witnessed in the past decade. Demand is growing at a steady clip, and now, the battle for market share is set to step up in intensity.

“Since we don’t have anything that is truly new since the ‘90s, it’s the next best thing,” said Dean Riechers, associate professor of weed science physiology at the University of Illinois at Urbana-Champaign.

For a formidable chemistry that has stood the test of time – its last reregistration in 2005 came only after the EPA evaluated it for 17 years – nowhere is a sign of its resurgence clearer than in a heavily anticipated blockbuster cropping system from Dow AgroSciences. In 2002, scientists at the Big 6 company pinpointed the budding glyphosate resistance problem and made 2,4-D the backbone of what it would, a decade later, call the Enlist Weed Control System. “The interest among farmers is extremely high. They need this technology now,” Joe Vertin, Dow’s global business leader for Enlist, said.

Now on its final stretch toward the US regulatory finish line, Enlist is targeted for a 2015 launch for corn, followed by soybeans the next year and later, cotton. The system provides robust tolerance to be stacked with glyphosate – in corn, with 2,4-D and FOP herbicides (less commonly known as aryloxyphenoxy propionates) – and, in soybeans and cotton, with 2,4-D and glufosinate.

Dow AgroSciences is counting on $1 billion a year in revenue from Enlist – about 18% of its 2011 sales of $5.7 billion. It also plans to bring the product to Canada as well as Brazil and Argentina, where concern over resistance is “growing at an exponential pace. Field after field is having problems with a weed much like our marestail in the U.S.,” Dr. Mark Peterson, Dow’s global biology leader for Enlist, told Farm Chemicals International in an interview.

Dow’s bet is that the diversity of novel traits and modes of action within Enlist, coupled with a rock-solid stewardship program, will provide growers with a long-term tool to help outsmart glyphosate-resistant weeds, which are surging by 25% per year in the U.S., according to third-party grower surveys.

Enlist Duo, the post-emerge herbicide that growers who purchase the system must agree to use together with the seed, combines glyphosate with a 2,4-D choline – a quaternary ammonium salt versus an amine or ester as in traditional formulations. Dow touts its reduction in physical herbicide drift by a factor of three compared with current technology. Vapor loss is also “essentially eliminated.”

“It’s a unique scenario in that it’s new technology but old chemistry,” Riechers says. “Normally, 2,4-D would kill soy or cotton – this is a unique tool that farmers have never had before.”

What 2,4-D and Enlist are not is a silver bullet: “We tried to design it to bring the same benefits that the growers have seen in glyphosate. Our objective is to bring it forward,” Vertin commented. “We’re going to use an integrated systems approach that, coupled with stewardship, will make the herbicide-tolerant cropping system sustainable again.”

Peterson refutes the suggestion that it too will face the same predicament as glyphosate. “The problem with the question, ‘When are we going to see resistance to Enlist?’ is that Enlist is not a single herbicide; it’s a system,” he says. “A lot of that is driven by the mentality created by current glyphosate-tolerant crops where a single active ingredient has been used on over 90-plus percent of acres over and over. Obviously, the industry, growers and weed science learned a lot from that experience of glyphosate overuse, that it’s not the way things need to be done.”

Not surprisingly, the road to bringing Enlist to market has proved longer than expected. Bayer CropScience filed three lawsuits against the chemical giant for patent infringement, none of which have been resolved, and all of which Dow claims are without merit. It has also battled regulatory delays and an onslaught of negative social media and press from anti-biotech/environmental activist groups such as the Center for Food Safety, which lobbied the U.S. government to stop the product’s deregulation. The group branded Enlist “Agent Orange corn” and cited decades-old controversies involving 2,4-D – even though current uses of the herbicide were judged by EPA in 2005 to pose “a reasonable certainty of no harm.”

A Teachable Moment

In one landmark decision in 2012, the Environmental Protection Agency denied a 2008 petition by the National Resources Defense Council seeking to cancel 2,4-D registrations and revoke all tolerances. NRDC sued EPA, citing concerns that use of 2,4-D “could increase by 50-fold or more” if USDA deregulates Dow’s product. EPA left no stone unturned in its 99-page response: “Based on studies addressing endocrine effects on wildlife species and the adequacy of personal protective equipment for workers, the Agency concluded that the science behind our current ecological and worker risk assessments for 2,4-D is sound and there is no basis to change the registrations,” it stated.

The impact of EPA’s decision is significant, according to Jim Gray, executive director of the Industry Task Force II on 2,4-D Research Data, which funds scientific research to meet the agency’s requirements. “It’s what my buddies call a ‘teachable moment,’ both to the pressure groups and the public in general, to how well EPA does its job and how thoroughly they evaluate all the available data in making these determinations,” he said.

If the future of 2,4-D looked gloomier, weeds of the world would seemingly have outwitted it by now, considering the chemical has been in use about four times as long as glyphosate. But thanks to the complexity of its mode of action, they haven’t. It’s no wonder why experts like Dr. Ian Heap of the International Survey of Herbicide Resistant Weeds expect 2,4-D use to grow. “Even when resistance is reported (in 29 cases), it has not been widespread like it was for some of the other herbicide groups like the ALS inhibitors, ACCase inhibitors and triazines,” Heap said.

Another benefit is that 2,4-D is typically partnered with herbicides of varying modes of action in a tank mix. “On the scale of what you are seeing across the [U.S.] South with other herbicide-resistant weeds showing up, 2,4-D has not experienced that even over 65 years of use within the ag community,” Gray said, noting that wise management is paramount.

“I would ask that we temper swapping one system for the other. We need to manage these in a long-term strategy so that we don’t develop resistance to another mode of action just because it’s the simplest, easiest, next step to go,” he cautioned.

Carving Out a Bigger Market

Chris Wu of CCM International, the Chinese chemical consultancy, expects output of 2,4-D technical to climb, partly driven by the larger market Dow will generate for its own proprietary product. “To some extent, the production of Dow’s 2,4-D choline will create more development space for the whole 2,4-D industry,” Wu told FCI. He warned that China is still oversupplied with the technical-grade chemical – a situation he does not expect to change dramatically over the next five years. “With the large expansion of production capacity in recent years, the supply of 2,4-D has highly exceeded its demand, and the operating rates of most manufacturers are very low,” he says.

Nevertheless, large-scale 2,4-D producers are expected to continue ramping up capacity to stay competitive. “Meanwhile, small-scale producers will be washed out during the intense market competition,” Wu said.

Alice Liu of King Tech Corp., a Shenzhen, China-based agrochemical trader, has seen the Chinese 2,4-D market grow steadily, as three more producers registered to manufacture the technical-grade product since 2011. “The price of 2-4, D tech and related products to the tech has risen as well through January 2012 since 2011. I believe demand and output will continue to increase,” Liu told FCI.

One challenge for 2,4-D is treating the pollutants created during production, and it’s only getting costlier with more stringent environmental requirements, Wu said. Making 2,4-D tech generates substantial wastewater, and other factors – blind expansion, price wars and illegal production among them – will also hinder development in China, he maintains.

China’s 2,4-D technical capacity topped 65,000 metric tons as of the end of 2011. Top producers include Changzhou Wintafone with 20,000 metric tons of capacity per year, and Shandong Rainbow and Jiangsu Huifeng, each with 10,000 metric tons. China has seen stable growth for use primarily on wheat, corn and soybeans, with the share of 2,4-D consumption in these crops rising to between 70% and 80%.

Major planting regions for wheat, corn and soybeans include Heilongjiang, Henan and Shandong, which are China’s biggest consumers of 2,4-D, according to CCM. The country exported 500 to 1,000 metric tons by volume to the U.S. between 2009 and 2011, and exports are expected to increase in the next five years.