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10 Dicamba Damage Takeaways From Missouri

Thinking about planting dicamba-tolerant soybeans in 2017? Learn some lessons from Missouri's 2016 experience.

If you’re planning on growing dicamba-tolerant soybeans in 2017, listen to Kevin Bradley’s take on Missouri’s experience in 2016. It will save you and your neighbors lots of grief.

Bradley, a University of Missouri (MU) Extension weed specialist, detailed the fallout that occurred when unlabeled and illegal dicamba formulations were applied in Missouri to dicamba-tolerant soybeans to those attending this week’s North Central Weeds Science Society meeting in Des Moines, Iowa.

Although federal regulators in 2016 approved soybean varieties in Monsanto’s Roundup Ready Xtend Crop System that tolerate dicamba and glyphosate for 2016, they didn’t approve dicamba formulations that match it during the growing season. Complaints in these states center around the allegation that existing formulations of dicamba not labeled for use on Xtend soybeans moved into and injured neighboring non-Xtend soybeans and vegetable crops.

“No amount of weed science training I had prepared me for what happened last summer to neighbor-to-neighbor relationships, with hearing about ‘knowing him all my life’ and that ‘my son went to school with his kids, and now we aren’t even talking to other’ – that sort of thing,” says Bradley.

Here are some takeaways from Missouri’s 2016 experience to keep in mind for 2017.

1. Dicamba really does a number on fruits and vegetables.
A dicamba-damage hot spot was Missouri’s Bootheel region. This southeastern section of Missouri produces a cornucopia of crops including corn, soybeans, vegetables, watermelons, and orchard crops.

If dicamba goes off-target, this is a bad place for it to happen. Off-target dicamba blitzed crops like tomatoes, watermelon, and peaches grown in this region. As of now, 120 cases of dicamba off-target movement in the Bootheel have been reported to the Missouri Department of Agriculture (MDA), notes Bradley.

2. It can happen in row-crop areas, too.

Bradley showed one north-central Missouri county where 10 official complaints were reported to MDA. This county grows 83,000 acres of corn, and 103,500 acres of soybeans. That’s typical of most Midwestern counties, and shows the potential for this to occur in various areas of the Corn Belt.

Statewide, 45,000 acres of soybeans were reported as dicamba-damaged, according to MDA. Bradley, though, thinks the actual amount is probably closer to 100,000 acres.

“Farmers don’t like to turn in other farmers,” he says.

3. Rural homes are sensitive sites, too.

Even before dicamba came along, the palms of many pesticide applicators became sweaty as they sprayed near high-dollar crops like grapes and tomatoes. Obviously, these areas have and still are considered sensitive sites and are labeled as sensitive areas.

They aren’t the only ones, though. Dicamba damage to homeowner gardens, trees, and ornamental bushes often doesn’t show up in damage reports, but it happens. This can threaten future use of tools like dicamba-tolerant technology by restricting agriculture’s social license.

“Homeowners are not stupid,” Bradley says. “If half of their tree is defoliated, they are going to ask, ‘OK, what happened here?’”

4. All types of off-label dicamba can damage sensitive crops and other vegetation.

Both the dimethylamine (DMA) salt formulations (Banvel, Rifle, etc.) and diglycolamine salt formulations (Clarity, Sterling Blue) of dicamba were involved in off-target cases. “The majority of cases were DMA,” he says. “But there were cases were DGA salts were sprayed as well.” All were illegal.

5. Just a little dicamba hurts a lot.

Ever notice the fizz that goes off a pop can when you open it?

Well, that amount is akin to the amount — 1/20,000 of the labeled rate of dicamba — that can injure soybeans, points out Aaron Hager, University of Illinois Extension weed specialist.
“With these Missouri famers, there was no malicious intent, says Bradley. “The number one thing they did not get, and maybe it was my fault in educational presentations I gave, is just how little dicamba it takes to damage their neighbor’s crop. There is data about what dicamba can do to soybeans dating back to the late 1970s, so we need to show it to make it clear to them.”

6. Illegal applications also had illegal rates.

Not only were off-label applications illegal, but rates for these applications often were illegal.

 “Larry Steckel (University of Tennessee Extension weed specialist), Jason Norsworthy (University of Arkansas Extension weed specialist), and I have no idea where they got the information to apply the 24-, 28-, and 32-ounce-per-acre rates, but that is what they did,” says Bradley. (In Clarity’s case for example, label rates are 8 ounces per acre for coarse, low-organic-matter soils and 16 ounces per acre for fine soils.)

 “We would walk in these fields and the comment would be, ‘But look at the weed control,’” says Bradley. “Well, yes, you can do lots of things if you are spraying (up to double) the label rate.”


7. Watch the boom height.

Nor were application parameters like boom height (no taller than 24 inches above the canopy) followed. That parameter will be challenging for on-label applications in 2017 and future years, believes Bradley. Maintaining a 24-inch height in the flat plains of the Missouri Bootheel is easier than in rolling fields, hills, and terraces that make up the topography of the rest of Missouri.

8. Be wary of applications in a 15-mph wind.

The label for Monsanto’s Xtendimax with Vapor Grip Technology (the only low-volatile dicamba formulation in Monsanto’s Roundup Ready Xtend Crop System approved by federal regulators so far) permits it to be applied in wind speeds up to 15 mph.

However, its label restricts applications when 10- to 15-mph winds are blowing toward nontarget sensitive crops. Optimal conditions for applications are when wind speeds are between 3 and 10 mph, provided all other label application requirements are met. Applications are restricted at wind speeds below 3 mph.

Even when conditions permit it, Bradley is wary of applications when wind speed approaches 15 mph. This wind level was rare in the Missouri Bootheel during peak dicamba application times in June and July in 2016, he notes. Still, off-target movement occurred.

“Based on what I saw in 2016, I would not want to get anywhere close to 15 mph,” he says.

9. Don’t be a nighttime dicamba sneak.

Some illegal dicamba applications occurred under the cover of night. These applicators might have fooled some unsuspecting neighbors, but they couldn’t fool Mother Nature. “If applicators spray at night, some of them spray right into a temperature inversion,” says Bradley.  

Temperature inversions often occur at night when cool air runs into warm air. During the day, soil warms as it absorbs soil radiation. At nighttime, though, this warm air rises while cooler air settles near the ground. This temperature inversion of warm air above cool air traps herbicide particles in a concentrated mass that can move and land off-target. This inversion often breaks at sunrise due to vertical air mixing.

Temperature inversions have commonly occurred in southeastern Missouri in recent years. Bradley, Mandy Bish, who is an MU senior research specialist, and Pat Guinan, Missouri state climatologist, tracked Missouri Bootheel temperature inversions in 2015 and 2016. In 2015 and 2016, 24 and 20 temperature inversions occurred in southeastern Missouri during June and July, respectively. Typically, these started from 7 p.m. to 8 p.m., and lasted up to 10 hours.  

“I know there are applicators who don’t have a clue what a temperature inversion is,” Bradley says. Making applicators aware of temperature inversions is a goal of MU weed scientists in 2017.

10. Talk to your neighbors. Really talk.

Bradley advises famers to communicate with each other prior to this next growing season. “Ask who is planting what where,” he says.

One tool Arkansas farmers have used for several years is a program called “Flag the Technology,” where flags on field borders are color-coded to the type of herbicide-tolerant system used in the field.

Besides economics, battles fought over off-target movement of herbicide can rip apart rural neighborhoods.

“The social impact cannot be underestimated,” he says. “You do not want to get into fights over this.”


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