Over the last couple years, new chemistries and respective genetics have entered the soybean market – including dicamba-resistant cultivars such as Roundup Ready 2 Xtend, and the glufosinate-resistant LibertyLink soybeans. Balance GT/LL soybean resistant to isoxaflutole and glufosinate and Enlist soybean resistant to 2,4-D choline, glyphosate and glufosinate may commercialize in the near future.
These new tools present some new options for controlling glyphosate-resistant weeds. It goes without saying that you shouldn't spray dicamba on soybeans that aren't dicamba-resistant, or glufosinate on non-glufosinate resistant soybeans. However, with multiple herbicide-resistant soybean cultivars available on the market, the question becomes: how do you keep track of which cultivar is planted where?
"Right now, we are concerned with all of the off-target movement of dicamba, but the basic concept here is the first thing we should know is which cultivar is in which field and that we need to apply the right herbicide," says Amit Jhala, Nebraska Extension weed management specialist. "If you apply an herbicide on the wrong soybean cultivar, it will be killed. That will be greater damage than off-target movement of dicamba or other herbicide. In off-target movement, you get a minor rate, because you aren't applying directly on top of that crop. Here you're applying at the labeled rate and there is no chance of survival. If you apply the labeled rate of new dicamba products [FeXapan, Engenia, or Xtendimax], that's a lot more than is needed to kill that soybean not resistant to dicamba."
Signage warns applicators
One practice Jhala recommends is using some kind of signage, such as different colored flags that can help remind applicators which kind of soybean is planted in which field, and what herbicide that cultivar is resistant to.
"Some growers farm 4,000 to 5,000 acres of land, and this makes it difficult to know which cultivar they've planted in which field, especially if they're planting different kinds of herbicide-tolerant soybeans on their farm," Jhala says. "About 50% of fields are being sprayed nowadays by commercial applicators, not by the owner of the field. That's a pretty big number in a state like Nebraska."
It isn't just sensitive soybeans growers need to watch out for. Nebraska is the No. 1 popcorn-producing state in the U.S., and although dicamba isn't much of a problem for popcorn, keep in mind popcorn isn't resistant to glyphosate.
"Unfortunately we don't have much information available about weed control in popcorn, but nowadays it's even more important," says Jhala. "If a grower has Enlist corn in one field and a neighbor has white or yellow popcorn, which isn't resistant to Enlist DUO herbicide – Enlist DUO contains 2,4-D choline and glyphosate – glyphosate can still kill your popcorn."
Last year, Jhala and PhD student Ethann Barnes at the South Central Ag Lab near Clay Center began studying the response of white and yellow popcorn hybrids to different rates of glyphosate, Enlist DUO and Xtendimax (dicamba with VaporGrip Technology), with about 26 different treatments.
"We are repeating this project one more year. The first year we found that a very minor rate of glyphosate, one-tenth the labeled rate, can kill popcorn completely. That's why we need to be careful. Popcorn isn't glyphosate-resistant," Jhala says. "Popcorn is also very sensitive to Enlist DUO, because it contains glyphosate. Dicamba is a labeled product even in popcorn, so we haven't seen much injury from dicamba in popcorn when applied at the labeled rate."
Don’t forget your neighbors
Moving forward, Jhala notes communication, not only between the landowner and applicator, but communication between neighboring farmers will be key — and with it, taking the necessary steps toward coexistence of different crops, cultivars and hybrids.
"Since last year, much of our focus has been off-target movement of dicamba on non-Xtend soybeans and other sensitive crops, but there are other herbicides that can be problematic when a sensitive crop isn't resistant," says Jhala. "I think it will be about communicating and keeping a buffer zone between sensitive crops, and when you apply post-emergence herbicides, make sure you watch your wind speed and direction. When the wind is blowing downwind to sensitive crop, make sure you don't spray. All those factors that can affect off-target movement of dicamba on sensitive soybeans can affect any other sensitive crops."
You can learn more about these topics and the latest research in weed management at the upcoming Weed Management and Cover Crops Field Day. The field day will be from 8 a.m. to 3 p.m. June 27 at the South Central Ag Lab west of Clay Center off Highway 6.