Dicamba Delivers Distress

Dicamba, a common herbicide meant to kill weeds, is proving to also negatively affect soybeans that aren’t yet adapted to the chemical.

The soybeans experience leaf cupping — an inhibition of sunlight intake that affects the photosynthesis process — and can lessen bean density within a few days of application of the chemical according to three North Dakota State faculty members; post doctoral research fellow Dipayan Sarkar, associate professor in the plant sciences department Kirk Howatt and professor and weeds specialist Richard Zollinger.

All of them spoke about what dicamba is and what it does. This herbicide is typically used to control broad leaf weeds and, up until recently, was mostly used in corn and wheat crops.

The reason it’s now used with soybeans, which is a broadleaf plant, is because a portion of soybean plants have become resistant to this herbicide.

That’s where the issue gets tricky. Only some soybean plants have the resistance, not all.

The problem some farmers are seeing is the demise of their soybean crop. There are a few possible reasons for this that all trace back to dicamba.

One possibility is the movement of the spray from one crop to another by a breeze coming through at the time the herbicide is distributed.

“It can vaporize and move to another plant,” Sarkar said, which is a problem when the crops aren’t resistant to dicamba.

“Most of the growers are still growing the Roundup ready soybean which is not resistant to dicamba, but you have some plot where you have Roundup and dicamba resistant, and then you spray (dicamba) there and it drifts with the air,” Sarkar continued. “That is what is causing the problems. These problems are more prominent where temperature is high. Most of the injury from dicamba is more prominent in the southern states.”

If this is the case, why are we using it?

“Dicamba has been registered since the mid-60s,” Howatt said, and because of rigorous testing, harm to humans isn’t a concern.

Why is this happening? Zollinger has four specific reasons he believes this issue is taking place.

“The first one is timing … Number two is the rate, wheat and corn were using very small amounts in soybeans we can apply half a pound of the active ingredient so we’re applying at a much higher rate … Number three, I cannot over emphasize this enough, that non-transformed soybeans are the most susceptible plant that we know of to dicamba … Number four is this, if we would’ve had are you wet or what or summer, I think a lot of this would not have happened,” Zollinger said.

To explain all this goes as follows:

In corn and wheat crops, it’s generally applied early in the growth of the plant, but in soybeans it’s used much later, even into the reproduction stages; it’s also applied at a higher rate.

Even if a farmer sprays their corn with dicamba and then doesn’t clean their instrument and goes and sprays their soybeans, traces of that dicamba can remain and affect the soybean crop. The wind can carry the spray for up to a mile if the droplets are small enough. When that’s carried to non-transformed or non-adapted soybeans, that’s detrimental to crops.

Dicamba is water soluble; if there’s a large amount of rain the dicamba will wash into the ground and no longer be effective as a herbicide.

“Worst case scenario are the financial problems and hardships for current producers,” Howatt said. “Litigation issues are another one of those situations where buyers are already involved and neither side is really going to see a victory.”

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