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Stewardship of Dicamba and 2,4-D Reviewed

Credit: www.deltafarmpress.com

Most of the farmers attending the 20th Annual Dekab-Asgrow-Deltapine Field Day in Union City, Tenn., made sure they attended the presentation given by Dr. Larry Steckel, professor, Weed Science, University of Tennessee. Steckel provided a comprehensive overview of varieties and acres planted to soybeans and cotton across the state, and how farmer stewardship of dicamba and 2,4-D fared compared, in part, to complaints filed with the Tennessee Department of Agriculture.

Based on what he has heard and seen this year, 75 percent of cotton acres in the Volunteer State are planted to dicamba-tolerant Xtend cotton varieties, with most of the remaining acres planted to 2,4-D-tolerant Enlist varieties. About 95 percent of soybeans acres are covered with Xtend varieties.

“If you do the math, Tennessee has 1.8 million acres of soybeans, so that leaves around 100,000 acres that are either LibertyLink, Roundup Ready, or conventional,” says Steckel. “That’s a big change from just a few years ago.”

Was the Technology Effective?

The weather, almost the entire month of May, was overcast most mornings with afternoons filled with rain. Those conditions, Steckel has seen, are not conducive to post-herbicide effectiveness — especially from Liberty herbicide. He advises spraying it in the middle of the day — and even then, it struggles to be effective. “It can be inconsistent, and our May weather added to that inconsistency,” adds Steckel. “But in June and July, it was money!”

Steckel had better luck in May with the dicamba products (Engenia or XtendiMax) because they seemed to be a little more forgiving or robust in that type of dreary weather pattern. He found out this year that Engenia and Enlist have a rain-fast period of at least two hours. In some places, he had a few weed escapes.

Producers called Steckel reporting they did not get adequate control from applications of XtendiMax or Engenia. While the applications might have knocked down pigweeds, it did not kill them. “They’ll grow slowly for two weeks or so after the application and then take off and grow 2 inches a day,” says Steckel. “You have to do something, or you’ll get in trouble quickly.”

Steckel’s advice included a follow-up application of Liberty to take out those crippled weeds. He has also seen effectiveness in soybeans with products containing fomesafen, like Warrant Ultra. Prefix and Flexstar have also provided control.

“I’ve made this recommendation for two years and nobody has called me saying it doesn’t work,” says Steckel. “If it wasn’t working, believe me, I would hear about it because farmers would let me know!”

Calls have increased from growers in southwestern Tennessee counties complaining about barnyard, goose, and Johnson grass problems. Resistance seems to be the culprit. A burndown was applied on one Tipton County field with a pint of 2-pound Clethodim (the maximum labeled rate) and a quart of Roundup, but it did not seem to faze the grasses.

“We took some of the weeds to our greenhouse to test them for resistance,” explains Steckel. “This has been one of the big changes I’ve seen this year, and we have to address it proactively.”

Addressing Stewardship

There were a high number of reported soybean injuries from dicamba drift. Steckel was called to one field in Lake County three separate times where dicamba applications over Xtend soybeans drifted to soybean fields planted to LiberyLink-tolerant varieties. If the drift occurs during growing stages, yield loss may occur, but if drift occurs around the R1 or first flower stage, particularly if multiple drifts occur, expect significant yield losses.

“We had a lot of that last year, which led to more regulation this year,” reminds Steckel. “It also led to more training for consultants, applicators, and scouts.”

Almost 3,000 applicators have taken the 50-minute stewardship module on auxin herbicides Steckel put together. He also created 13 blog posts that were accessed almost 4,000 times and created 25 in-season YouTube videos on stewardship management that were viewed over 17,000 times.

“The EPA and TDA wanted education efforts increased after the high number of complaints in 2017,” adds Steckel. “We’ve had about 30,000 acres of soybeans showing injury from dicamba drift, compared to 400,000 acres last year.”

Those numbers indicate a 90 percent reduction in dicamba-related injury to soybeans compared to 2017. Extension personnel investigated a lower number of 2,4-D drift complaint calls this year, but as far as Steckel knows, there has not been one 2,4-D complaint filed with the TDA.

During his presentation, Steckel shared one picture of Drake Copeland, a Ph.D. graduate student, holding a healthy Extend soybean plant and a LibertyLink soybean plant that was extremely stunted. “The LibertyLink plant got dinged really well with dicamba drift from an application over the Xtend soybean field,” explained Steckel. “It never recovered.”

One of the more interesting scenarios Steckel described involved a logistical slip when two 90-foot sprayers were used to spray from two different totes of XtendiMax. The cotton sprayed with one sprayer looked fine, but damage to cotton leaves was obvious in the other field.

“I started looking at the sprayer that was used on the injured cotton, and the pump on that sprayer was supposed to be used for Enlist only,” says Steckel. “The pump that was used to previously spray 2,4-D was contaminating every shot. I have been back since to the injured field, and it had recovered remarkably well.”

Specialty Crops

Most crop injury reports in 2017 were farmer-to-farmer. This year, the TDA had complaints from homeowners and landscapers about damage to Paulownia, sycamore and redbud trees. Steckel responded to an injury call last year to a Tennessee tobacco field where plants had “cobra-shaped” leaves — a telltale sign of dicamba drift damage. Testing confirmed the presence of dicamba.

“Once that happens, that farmer automatically loses the contract for that tobacco, and at $10,000 an acre, that smarts,” says Steckel. “What’s worse is the same farmer called me this year, and the same thing happened, so he is recommending no dicamba be used in Tennessee counties where tobacco is grown.”

The overriding question for many growers is whether they will have dicamba for Xtend crops in 2019. The labels for Engenia and ExtendiMax expire this fall. Steckel knows the EPA will be taking a hard look at how well the product was stewarded this year. “The easiest thing for them to do is nothing,” says Steckel. “If they do nothing, the labels will expire.”

The original news story can be accessed here.