As growers across the Midsouth wrestle with how best to combat increasingly herbicide-resistant weeds in cotton, soybeans and other major row crops, weed scientists at the University of Arkansas System Division of Agriculture are striving to shed light on dicamba, one of the potential new tools today in the fight against Palmer amaranth, commonly known as pigweed.
Farmers and applicators need to be fully aware that Dicamba is a major concern for neighboring farms. The herbicide can prove highly damaging to crops, especially soybeans, which aren’t resistant to dicamba.
Quick Dicamba Facts
- Broadleaf weed herbicide. Almost a 50 year history of use on some 200 weeds.
- Group 4, auxin-based herbicide. Kills target plants by disrupting normal growth patterns.
- High degree of volatility. It is a benzoic acid and in an “unmixed” state after application, Dicamba easily evaporates and can become wind-borne, which can lead to off-target drift.
Bob Scott, professor of weed science for the Crop, Soil and Environmental Science Department at the University of Arkansas System Division of Agriculture, said there are currently 4 formulations of dicamba on the market.
“Dicamba was developed a long time ago, and is one of the oldest chemistries we use in agriculture,” Scott said. “The ‘acid formulation’ is dicamba in its most volatile form. Think of it as just the dicamba molecule by itself, without anything attached to it. It’s still sold and used in various formulated products.”
Scott said successive formulations of dicamba have come along in the decades since, each adding progressively larger, heavier salts. Banvel herbicide, for example, is dicamba combined with dimethylamine, or DMA, salt.
Clarity herbicide was later developed by BASF, combining dicamba with diglycolamine, or DGA salt. Monsanto is now marketing this same formulation as Xtend, Scott said.
BASF will soon begin marketing an herbicide known as Engenia, which is dicamba combined with sodium methylamine, or BAPMA salt.
Herbicide Resistance Info
“The BAPMA salt doesn’t have anything to do with an additive,” Scott said. “It’s an actual change in the salt attached to the dicamba molecule. They’ve added some stuff to that molecule, and they’ve significantly reduced the volatility of the dicamba molecule itself.”
Although Engenia hasn’t received a federal label yet, industry experts and weed scientists expect a positive decision by the end of the year.
The Arkansas State Plant Board is scheduled to meet Nov. 21 and hold a public comment hearing on proposed changes to regulations governing the use of dicamba herbicides in Arkansas.