Farm Progress

Know where NOT to spray new dicamba or 2,4-D because eyes are watching

Gears are in motion for Southeast cotton and soybean growers to legally apply auxin herbicides in-season. It is important to know where NOT to spray them. People will be watching.

Brad Haire, Executive Editor

January 23, 2017

6 Min Read

Gears are in motion for Southeast cotton and soybean growers to legally apply auxin herbicides in-season to new seed traits tolerant to them. Each label comes with major restrictions, and every detail should be followed. But it really boils down to a simple philosophy: Know where NOT to spray them. People will be watching.

Auxin herbicides expected to be cleared at the federal and state level for legal in-season use in the 2017 cropping season on resistant seed are Monsanto’s Xtendimax with its new dicamba formulation, BASF’s new dicamba formulation sold as Engenia and Dow AgroSciences’ Enlist Duo, which includes its new 2,4-D formulation.

With the corresponding resistant seed technologies for dicamba or 2,4-D systems available for cotton and soybeans, coupled with the legal clearance to use the herbicides, the stage is set for “significant adaption across our state and definitely across the region,” which will be done to manage hard-to-control weeds such as Palmer amaranth, morning glory and to a certain extent tropical spiderwort , said Stanley Culpepper, University of Georgia Extension weed specialist.

“Keep in mind, our cotton industry has invested over $1 billion just to control Palmer amaranth (in the last decade),” he said. “We (cotton growers) desperately need help and new tools to manage this pest. We’ve lost some conservation tillage (due to the problem). We’re doing more tillage. The use of herbicides and our herbicide input cost has skyrocketed to control this plant.”

Georgia cotton farmers in the past several years, including in 2016, are having to hand-weed 85 percent of the state’s cotton crop, even with good, timely management strategies. “Of course growers should be commended for this effort as it is arguably the single-most important step in preventing additional herbicide resistance development,” Culpepper said.

Slightly improved control

“In research-grade Palmer amaranth populations, the new technologies do offer slightly more flexibility and improved control over our standard practices with a few dollars less in hand weeding costs at seasons end,” Culpepper said. “It is critically important we have standard programs equally effective, allowing grower’s options. Those equally effective options do exist for most Georgia fields, but we do need to continue to improve our standard programs for the fields with heavy infestations.  For our growers who are able to be timely and aggressive, they are already achieving effective control with standard programs that offer lower off-target drift risks.”

The new auxins are formulated, and their labels written, to reduce the risk of off-target, drift-related crop damage.

It’s been reported for several years, and it’s no secret, that vegetable and specialty crop farmers are concerned about the introduction of the new technology, especially into Georgia’s diverse agricultural landscape, said Culpepper, speaking Jan. 6 at the annual Southeast Regional Fruit and Vegetable Growers Conference in Savannah. Many major high-value Georgia vegetable crops, as well as major row crops not resistant to an auxin, are highly sensitive to these herbicides.

“From my office (in south-central Georgia), I can be in 35 different crops in 45 minutes. We grow them all year round and grow them all in the same areas and often by the same grower,” he said. “If you look at our farmgate value and look at our agronomic crops versus our specialty crops, and you look at when they’re grown and where they’re grown, I think we have more potential conflict for potential drift (problems) than anywhere else on the planet. So, we are really going to have to be better than we’ve ever been if we are going to avoid any of these issues.”

In 2016, there were no dicamba-related drift complaints reported to the Georgia Department of Agriculture or UGA Extension, which surprised officials in the state. It was not the same in the Mid-South, where crop damage due to illegal applications of dicamba in season prompted the EPA to issue a compliance advisory, something it rarely does, for the region. In Missouri, illegal dicamba applications have brought down 21 indictments so far.

Crop sensitivities

Starting in 2015 and into 2016, UGA Extension and the GDA, along with some industry representatives, initiated a training which is required to make in-season auxin herbicide applications in Georgia. The trainings are being offered in 2017, too.

“The only thing that is guaranteed to avoid these (off-target) issues is knowing where not to spray these products. Understanding the sensitivity of the crops around you can help you determine where you should and should not apply these products,” Culpepper said.


Culpepper and fellow UGA weed specialist Eric Prostko conducted 64 field trials applying dicamba and 2,4-D (at rates >1/75X, between 1/75 and 1/300X, between 1/300 and 1/800X and < 1/800X) to measure a specific crop’s visual sensitivity to the herbicides, rating each crop’s sensitivity to the herbicides in four categories: lower, moderate, severe or extreme.

Using their sensitivity reference, for example, tomato and watermelon’s visual sensitivity to Roundup would rate in the ‘ultra-lower’ category.  “Now, everyone knows tomato and watermelon are very sensitive to Roundup, but the point is that the scale has changed with dicamba and 2,4-D for many crops. For example, dicamba poses much greater threat to these crops and ranks in the ‘severe’ sensitivity category,” Culpepper said.


“One of my favorite quotes that drives me nuts: ‘If you’re doing a good job with Roundup, you’ve got no problem with in-season 2,4-D or dicamba applications,’” he said.

Not true. Culpepper pointed out that some crops widely grown in Georgia are 10 to 20 times more sensitive to dicamba or 2,4-D than to they are o Roundup.

Registrations can go away

Speaking Jan. 6 at the Southeast Regional Fruit and Vegetable Growers Conference, Rick Keigwin, deputy director of programs for EPA’s Pesticide Program office, reminded growers the dicamba registrations have two important time restrictions:

1) Both Monsanto’s and BASF’s registrations automatically expire in November 2018 unless EPA takes action to renew them.

“And what we’re going to be looking at over the next two years is, ‘Are the off-sight drift incidents continuing? To what degree are they continuing? Are they getting worse or are they getting better? Is the magnitude increasing?’” Keigwin said. “And if we determine that that frequency of drift events is unacceptable, they (the registrations) go away.”

2) If the registrations for new dicamba formulation are renewed in November 2018, they will automatically expire three years later. At that time, EPA again will look at drift incidents and also at where things stand with resistance issues. The registrations go away if things are not acceptable.

The bottom line: If EPA doesn’t take action on either deadline for the dicamba registrations, the registrations go away. “So, we all have to be partners to make sure these products are used the right way so that we don’t have the types of things that happened in the Mid-South,” Keigwin said.

Dow’s Enlist Duo 2,4-D formulation will have a five-year term of registration. “It’s five years for Enlist because we haven’t had the drift events like we had for dicamba, and that five years is primarily focused on resistance management,” Keigwin said.

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