Weed control isn’t about killing weeds; it’s about protecting yield—and the stakes are high. The challenge is not only gaining control of weeds this year, but every year following while herbicide resistance is building. It is logical that ag professionals have some farmer convincing to do when money is involved in this down ag economy.
Growing a successful crop is more complex than just spraying glyphosate, or any other single mode of action. Weeds are harder to control, are resistant to more herbicide groups and can steal bushels—a lot of them. Agronomists and consultants have to convince farmers to be mindful of these weed management best practices:
- Apply multiple, effective modes of action.
- Consider new traits or herbicides.
- Use both pre-emergent and residual herbicides.
- Scout to apply herbicides at the appropriate time and rate.
- Try mechanical weed control.
Applying only one mode of action will increase the rate and frequency of weed resistance. “What we see is nature fighting back,” said Aaron Hager, University of Illinois associate professor of weed science. When farmers overuse a single herbicide mode of action, it imposes selection pressure, which means more resistant weeds are produced, he says.
Farmers have to be educated about the difference between a herbicide active ingredient and a herbicide group. Sometimes a simple switch isn’t as easy as it sounds. Farmers should appreciate being shown the herbicide group number on a label.
Scouting to determine which weeds are the problems and which groups will work have become mandatory. Farmers need help to identify the herbicide groups that work on their farm and plan a method of attack. It is key to make sure the herbicides have at least two different and effective sites of action to keep from wear out a single site from overuse.
“There are obviously alternatives, but it’s not as simple as you think,” Hager said.
Among new alternatives expected for 2016 are technologies from Dow AgroSciences and Monsanto Company. Although somewhat extraneous for this discussion of herbicide resistant weeds, Bayer is coming up with new technology for 2018.
Bayer anticipates launching HPPD-tolerant Balance GT soybeans in 2018, pending regulatory approvals. These soybeans will be paired with Balance Bean herbicide, which contains HPPD (group 27) and glyphosate (group 9).
“The initial offering will have gytol, glyphosate tolerance and the next season we’ll add glufosinate (group 10) tolerance,” said Brent Philbrook, Bayer regional manager of field operations research and development in the Midwest. “Not only does [Balance Bean herbicide] have residual, it has reactivation.”
The residual is said to last eight to 10 weeks. During that time, it can be reactivated with rainfall to control later-emerging weeds, Philbrook says.
After more than a decade of research, regulatory hurdles and testing, Bayer is in the final stages of approval for this product. As with any single modes of action, failure to use this product as recommended could lead to reduced effectiveness in less time than it took to bring it to market.
Philbrook encourages the use of pre-emergent herbicides with residual; use Balance Bean or Liberty (glufosinate, when the trait is available) for post-emergence applications and scout to make sure the herbicides are effective. The addition of glufosinate tolerance allows rotating modes of action every year to help decrease the frequency of resistant weeds, he says.
In 2015, Dow AgroSciences introduced Enlist corn and seed production of Enlist soybeans. The company hopes to have a full launch of the Enlist platform in 2016, pending renewal of regulatory approval. The platform includes corn, cotton and soybeans. All Enlist crops will provide 2,4-D (group 4) and glyphosate tolerance. Soybeans and cotton also include glufosinate tolerance.
“We created Enlist because there was a need to control weeds and slow resistance,” said John Chase, Enlist commercial leader for the U.S. The system uses Enlist Duo herbicide with Colex-D Technology, which has a new 2,4-D and glyphosate formulation.
Dow says the new formulation diminishes risk to farmers and applicators. “Enlist Duo with Colex-D Technology decreases risk to a near zero volatility formulation,” Chase said. “It’s 96 percent less volatile than 2, 4-D ester with 90 percent reduction in drift.”
Chase says this dramatic decrease is caused by the new formulation and by using low-drift nozzles that create bigger droplet sizes to reduce drift. In addition to protecting farmers’ liability from drift, Dow has a detailed stewardship program to minimize the risk of misuse.
Monsanto is gearing up Xtend soybeans for a 2016 launch with expected approval of the Xtend production system products. Soybeans with the trait will be tolerant to dicamba (group 4) and glyphosate. The soybeans join Xtendflex, introduced in 2015, for cotton with tolerance to dicamba, glyphosate and glufosinate.
Hype about Xtend is recent, but testing is not. “We had Roundup Ready Xtend soybeans on our research farm as early as 2007,” said Dan Childs, Monsanto weed management technology development representative.
The Roundup Ready Xtend soybeans will be paired with Roundup Ready Xtend herbicide with dicamba-glyphosate premix or XtendiMax herbicide. A new formulation of dicamba has been made to reduce off-target movement and volatility.
“Banvel is a DMA salt, with a reputation of volatilization. We are using a different salt, a DGA salt, which along with VaporGrip will lower dicamba’s volatility,” Childs said.
“Roundup is there to control grasses, and what’s left is the dicamba to control the Roundup-resistant weeds,” Childs said.
Monsanto hopes overlapping residuals will avoid quickly building a tolerance to this program.
BASF Crop Protection offers an additional dicamba option for dicamba-tolerant soybeans and cotton. “Engenia will be an effective new tool with BAPMA salt on the core dicamba molecule to reduce volatility,” said Chad Brommer, BASF technical marketing manager for herbicides. “Engenia herbicide is awaiting EPA registration.”
New technology can be helpful, but it’s not a silver bullet—use is being recommended with pre-emergent, residual herbicides.
“The silver bullet has been tarnished for years and is never coming back,” Hager said. “[You need to] use technology in a stewarded systems approach.”
Spraying weeds when they are less than 4 inches tall is a standard recommendation. Starting clean at planting is also very important, which means needing to have a good pre-emergent down.
It is important to stress to farmers that some weeds, such as waterhemp and palmer amaranth, can grow 2 inches per day in certain conditions. Waiting 21 to 28 days after planting for a post-emergent application can cause severe yield loss and build the weed seed bank faster. Pre-emergent herbicides with residual can hold off weed problems until canopy.
Scouting following each herbicide application, including post, to make sure the herbicide is effective and the timing is correct should be a standard practice.
Farmers often jump to conclusions about their weed control, but they have to check to see if there was a weather event, sprayer malfunction, other application error or if the pre-emergent herbicide didn’t work. They will undoubtedly call for help in sorting out the situation.
It has to be stressed to farmers that timing, rate and efficacy are essential when it comes to post-emergent weed control. Lower-than-labeled rate herbicide use can increase the likelihood of resistance and ineffective herbicides allow resistant weeds to thrive, and this is extremely important to stress.
Lower-than-recommended rates are part of the reason resistance has spread across the U.S. “You may think, ‘I can save money by reducing rates,’ but don’t,” Hager tells farmers. “The expenditure column is directly related to the revenue column when it comes to weeds.”
Another point that might need stressed in this down economy for farm income is that buying a herbicide with greater weed resistance just because it has a lower price tag is very unwise. It could make fields a breeding ground for resistant weeds.
“The most critical message is don’t let weeds go to seed,” said Jeff Carpenter, regional corn and soybean portfolio manager for DuPont Crop Protection. He says to include products that bring multiple modes of action that are effective against the weed spectrum of each field.
Scouting will show if the timing and rates were right and if the herbicide was effective. The priority is to maximize weed control and minimize the spread of resistant weed seed. “You cannot replace scouting,” Hager said.
If weed escapes, farmers should consider using tillage or hiring a chopping crew to reduce weed seed spread during harvest. While the thought of dusting off the cultivator or disk or hiring a crew might sound like a time, money and resource suck, it could be the only way to save a farmer’s field. In some fields, especially no-till or extremely weedy fields, it could cost less than using ineffective chemicals.
“Any weed that goes to seed is a yield robber for future years,” Hager said. It is something that farmers must recognize in this time of tight margins in producing a profit.
Farmers seem to become aware of resistant weed problem when it’s way too late, and the message to farmers should be that if they are still using one mode of action, they will build resistance—it’s just a matter of time.
Farmers have to be convinced to be proactive. Hager said farmers have to be told, “If you cut back on yield-reducing pests and weeds, you increase your returns.”