Herbicide Systems 2.0: Life Beyond Dicamba
The next generation of herbicide-resistant crop systems will feature some older chemistries, presenting new challenges for applicators.
May 1, 2012
Dicamba has enjoyed a long and productive life in the weed control world. Velsicol Chemical Co. introduced dicamba under the brand name “Banvel” back in 1967, and it has been a reliable weapon in the arsenal of retailers for the past 45 years.
Now, dicamba is being prepared to take center stage in the next battle against Glyphosate-resistant weeds that have significantly compromised the effectiveness of the standard Roundup Ready System. An entirely new program featuring a new trait and a dicamba formulation “face lift” is being prepared that will provide a new weed control option for your growers.
According to BASF, dicamba is the fifth most widely used herbicide worldwide with approximately over 20 million acres treated, and thus far there has been little reported resistance developed to the chemical.
Dicamba works simply by mimicking a naturally occurring plant hormone, thus causing uncontrollable growth in the targeted weed. At high levels of exposure, the growth becomes so severe that the unwanted plant, or weed, dies off as a result. Dicamba, which usually comes ready to tank mix in a salt form, has several accepted methods of application, including ground or aerial broadcast, soil treatment, injection and spot treatment. It is reported to be both highly mobile in and poorly absorbed by most soil types, especially the harder Midwestern clay-based soils, further advancing the need for careful application and proper stewardship.
“BASF has more than 50 years of experience working with the dicamba molecule,” said Mike Hofer, BASF Corn Market Manager. “And throughout those 50 years we’ve constantly innovated the molecule. If you look back to when we introduced Banvel, and then Clarity back in 1992, and now on Engenia, in each step we’ve made advancements in the formulation to decrease volatility.”
With this advanced formulation, BASF’s goal was to reduce volatility dramatically, says Hofer. “In fact, we have five different methods to measure volatility and each method proves that Engenia will be the lowest volatility formulation of dicamba on the market.”
“Volatility is obviously a concern with dicamba and other similar molecules like 2,4-D,” says Dan Wright, Monsanto’s Dicamba Formulation Development Lead. “But dicamba’s (volatility) is also really pretty low and difficult to measure, so we have to use sophisticated methods to measure it.”
One test is the use of a Humidome, which involves spraying and then covering flats of soil with a plastic dome, then pulling air through the dome to expedite and better measure the volitalizing process.
"It takes us pulling air through the Humidome for 24 hours to be able to get enough of the material to be able to test for it,” he continued. “We’re looking for parts-per-trillion in the air, and that’s like putting an eye dropper of liquid int an Olympic size swimming pool.”
The Humidome trial revealed that Engenia, when compared with Banvel and Clarity, offers a 40% reduction in volatility.
The Spray Drift Question
Another area of important concern with dicamba, besides the volatility of the chemical itself, is spray drift. Dicamba is highly mobile in both the air and soil, as well as toxic to a wide variety of sensitive plants. So even with reduced volatilization built into the new formula, it is still a significant factor that must be accounted for when applying dicamba.
“They’re going to have to prove to the EPA that they have a product that not only controls weeds as well as the stuff we’ve been using, but also poses a lower risk for off-site movement,” says Bill Johnson, Professor of Weed Sciences at Purdue University. “There’s going to be a lot of pressure on them to do those kind of things in order to get this technology approved.”
According to Wright, one of the most difficult aspects of diagnosing spray drift is the length of time it takes for symptoms to appear.
“What happens with auxin herbicides like dicamba is that it takes about a week to 14 days before you start seeing spray drift damage,” says Wright. “So, a lot of growers think ‘Well, I didn’t see that injury for a week or more so the material must’ve gotten up and walked off the field after I sprayed it.’
"In reality it was probably some kind of spray drift, like spraying in a high-wind situation or with the wrong nozzle,” he continues. “So, it really happened when you actually applied it, but you don’t see that effect until a week or two weeks later.”
“Like with any crop protection product, spray drift must be managed,” says Hofer. “One of the things were currently doing in the market is stressing our “Triple A Activity” with herbicides. So, that’d be using the proper adjuvant, the proper air induction nozzle, and of course training applicators on making sure they’re cognizant of air space.”
Providing hands-on expertise to those applicators is the purpose of the 2012 On Target Application Academy, through which BASF and Monsanto recognized the opportunity to educate applicators alongside Dr. Robert E. Wolf, Manager of Wolf Consulting and Research LLC and an Application Technology Specialist for TeeJet Technologies Inc.
“We’re really proud to be launching our On Target Application Spray Academy, which is specifically designed to help growers and retailers understand how to apply crop protection products properly,” says Hofer.
The academy will be held throughout the year all over the country at industry events and is a free program that includes classroom presentations and hands-on learning opportunities. The sessions will reportedly cover an array of topics including:
- Best practices for self-application.
- Equipment clean-out.
- Nozzle selection and demonstration.
- Plant Biology.
- Sprayer set up.
- Understanding product labels.
“Obviously the number one goal of any application is to have good weed control, and right along beside that you have to have good drift management practices,” says Dr. Wolf. “We need to get growers and commercial applicators in the frame of mind that, if they are going to apply these products, they need to select and use a spray nozzle correctly so that they don’t create the drift that is possible when using some of the older spray nozzle technologies.”
“We’ve done a tremendous amount of work in understanding what types of nozzles we want to recommend and selecting those that will reduce drift, keeping this product on target,” said Joe Sandbrink, Monsanto Product Development Manager. “This going to be a great tool in addition to our Roundup Ready Plus solutions.”
Avoiding More Resistance
Aside from spray drift, another concern with increased dicamba use is the prospect of developing a resistance in some weeds down the road due to an overuse of the technology.
“I think history has hopefully taught us, and any of the companies that claim that it will never happen - that it will happen,” says Johnson of dicamba-resistance. “We already have dicamba-resistant weeds so it’s not like anyone can stand there and say it’s never going to happen. How soon will it happen? It’s really hard to tell. But we’re at the point now where we need new tools for soybeans, and dicamba is certainly going to help us in that regard.”
Specifically, dicamba-resistant waterhemp is one weed that experts expect will present a significant challenge.
“Certainly the biggest concern right now is dicamba-resistant waterhemp,” says Dr. Ian Heap of the Weed Science Society of America. “It has already evolved and with the adoption of the new synthetic auxin-tolerant crops there will be widespread resistance in waterhemp.”
Still, even with the growing possibility of increased resistance, Heap cautions against completely writing off such a useful tool.
“As with any herbicide site of action, if it is overused it will fail,” says Heap of the Engenia formulation. “But we don’t condemn the technology, as it will be very useful in rotation/combination with glyphosate. We just caution people on overreliance.”
One way to avoid dicamba overreliance is using the herbicide in combination with other weed management strategies, such as field scouting and in pre-and post-application tank mixes fortified with glyphosate.
“If anything it’s not just one thing, its multiple ways to control weeds in a system,” says Hofer. “It’s a systematic approach for weed control. There’s certainly no magic bullet and because of that we need to integrate a planned approach to weed control. There’s a strong history of successful applications with dicamba and certainly we recognize that Engenia will be a part of that successful ongoing history moving forward."