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Dicamba | Too Hot to Spray

Farmers and retailers have been under pressure this season to get herbicides applied to soybeans and it has caused a lot of headaches. A Ninth Circuit Court of Appeals ruling caused a five-day pause in the application of three of the four available dicamba products. In Illinois, unlike other states, that pause was upheld and then the state tried to remedy the situation by adding five days to the application window - which now closes June 25th. Mostly it is going to be too hot spray during that time frame. Another regulation prohibits application on days warmer than 85 degrees says University of Illinois Extension Weed Scientist Aaron Hager, “Looking at the long term forecast from the National Weather Service, it looks like the next five days will be a no-spray situation. We’ve high temperatures well in excess of 85 degrees for today, Friday, Saturday, Sunday, and on into Monday. So, of the seven days we have left, it looks like on the extended forecast there may be only about two days.”

Regulations require the forecast to be checked within 24 hours of the intended application says the ILLINOIS Extension Weed Scientist, “The forecast can change over time but it looks like, at least for the next several days, we are going to have to leave the Dicamba sprayers parked.”

That’s for the Dicamba resistant soybeans. Other soybeans just look awful. There have been herbicide products for decades that burn the leaves of soybeans and then they grow out of it but this year’s damage is, well, in a word serve. Again, here’s ILLINOIS’ Aaron Hager, “A couple of possible reasons why that could be the case. 1) The environmental conditions, obviously, when these were applied. If they are applied under very warm air temperatures under bright sunshine we tend to see more soybean response compared with applications that happen under cooler and perhaps cloudy skies.”

The other possible explanation lies in the practice of adding a residual herbicide into the post-application herbicide mix. Hager says some of the residual herbicides could be acting in the tank mix like an additional crop oil. This would lead to a more rapid uptake of the herbicide and a consequently quick and extensive development of the burning leaf symptoms.

Returning to Dicamba soybeans. Illinois farmers unable to make applications by June 25th will need to use alternative products; Glyphosate, PPO inhibitors, or both. The problem is that waterhemp is likely to be resistant to one of the two, and maybe both. If that is the case, Aaron Hager says there are no good chemical options for the field.

Dicamba & the National Family Farm Coalition

Dicamba herbicide products designed for use with GMO cotton and soybean have been pulled from the marketplace, or at least are in the process of being pulled. This is the result of a lawsuit filed by plaintiffs including the National Family Farm Coalition. Todd Gleason talked with the president of NFFC about the reasons why the farmer organization felt compelled to go to court to keep Dicamba, in this latest form, off the market.

How to Properly Use Dicamba on Soybeans

read farmdocdaily article

As the growing season approaches it is important for farmers to understand how to use dicamba on resistant soybean varieties. Todd Gleason has more with University of Illinois weed scientist Aaron Hager.



The following is an excerpt from the March 23 farmdocdaily article posted by University of Illinois Weed Scientist Aaron Hager.

Steps for Successful Weed Management in Dicamba-Resistant Soybean

Step 1
  • plant dicamba soybean seed into a weed-free seedbed
  • achieve a weed-free seedbed through the use of preplant tillage, an effective burndown herbicide(s), or a combination of tillage and burndown herbicides
Step 2:
  • select and apply within 7 days of planting a soil-residual herbicide that targets your most problematic weed species; if desired (and labeled), add dicamba and an appropriate buffer
  • for waterhemp or Palmer amaranth, select a product containing the active ingredients from one of the following categories of control:
Excellent Good Acceptable
sulfentrazone pyroxasulfone     S-metolachlor/metolachlor
flumioxazin metribuzin acetochlor
fomesafen+metolachlor     dimethenamid pendimethalin
  • Excellent: greatest efficacy on Amaranthus species and longest residual control
  • Good: good efficacy on Amaranthus species, residual control generally not as long
  • Acceptable: stronger on grass species but with some activity on Amaranthus species
Step 3:
  • scout fields 14 days after planting, apply dicamba at 0.5 lb ae/acre when weeds are less than 3 inches tall and when conditions allow for the application, consider adding an approved soil-residual herbicide to the tank mix
Step 4:
  • scout treated fields 7 days after the dicamba application; if control is not complete or another flush of weeds has emerged, consider using non-dicamba options for complete control; examples include alternative herbicides, cultivation, and hand rogueing; the goal should be zero weed seed production

DICAMBA | U of Arkansas Takes a Stand



Statement from Dr. Mark Cochran, Vice President-Agriculture for the University of Arkansas System Division of Agriculture, on Monsanto’s petition to the Arkansas State Plant Board

First, and most importantly, we stand by the integrity of our scientists and their science, including Dr. Jason Norsworthy, our internationally recognized researcher and his work, and all our weed scientists, as well as other public weed scientists on record in other states.

We are confident in the science that we’ve used to advise the regulatory process in Arkansas.
Even Monsanto recognizes his reputation. Just 48 hours before the petition was filed, the company invited Dr. Norsworthy to present a summary of national drift and volatility research at an academic summit on dicamba that the company is hosting in St. Louis this month. He has declined this invitation.

We will examine every point in this petition and its appearing and disappearing group of supporting exhibits, and over time will respond factually to its major points.

There are several points in the petition we need to address immediately: First, Norsworthy’s findings are anything but an outlier. It is consistent with research work in other states, including that of Kevin Bradley in Missouri, Tom Mueller and Larry Steckel in Tennessee, and elsewhere.

Second, none of our researchers has ever endorsed any product, but sometimes companies use our public comments and statements without our permission.

Based on Monsanto’s allegations, we intend, under the terms of our agreements with Monsanto, to publish all data relevant to our dicamba work over the last few years.

This petition isn’t just about a single herbicide, but it’s an attack on a whole profession – scientists whose careful work is meant to be of benefit to all.

We have made our explanations available to the public, including at field days and through videos of the presentations that were and are still public on the Cooperative Extension Service site, www.uaex.edu. Our public land grant research results are scientifically vetted and valid, and we are pledged to being transparent in our results.

Link to Dicamba in Arkansas - Research and FAQs

Check Dicamba Soybeans After Spraying

Farmers are turning to an old technology this year to control weeds in their fields. Here’s what they can expect from a new, old-product.

Dicamba has been around for about half-a-century. It is a corn herbicide, but soybeans have been modified to tolerate it. This was done because so many weeds have modified themselves to resist being killed by glyphosate, commonly known as Round-Up. The primary problem, says University of Illinois Extension Weed Scientist Aaron Hager, is waterhemp, “it, has never been excellent on any of the pigweed species. It can be good. It can be very good, but it is not excellent. It is not as consistent.”

This inconsistency makes the timing of dicamba applications extremely important. Without a doubt, says Hager, most post applied herbicides are going to do a better job of controlling a full suite of weeds in a field when the weeds are less than three to four inches in size, “Certainly, with something like dicamba and waterhemp, our recommendation to farmers is to treat very, very small weeds, but to go back in about 10 to 14 days and to scout those treated fields. Look to see what the efficacy has been. Sometimes we can twist up these pigweed plants, but that doesn’t mean they will necessarily be completely controlled.”

Look to see what the efficacy has been. Sometimes we can twist up these pigweed plants, but that doesn’t mean they will necessarily be completely controlled.

It is possible for the weeds to recover, flower, and produce seed. And that, says Aaron Hager, is something to avoid.

Dicamba Soybeans | how to manage herbicide applications

read more from Aaron Hager, University of Illinois Extension

Farmers going to the field this spring will be using a brand new type of soybean. Todd Gleason has more on why dicamba-resistant varieties will require them to exercise caution when making herbicide applications.