What is in this article?:
- Resistant weeds increase complexity of herbicide programs
- Pigweed: "An amazingly resilient plant"
- Timely preemerge, postemerge applications important
- A longer window of vulnerability
With the proliferation of herbicide-resistant weeds in crop fields, Larry Steckel has some not-so-good news for Mid-South farmers: “Nothing about weed control is going to be as easy as it once was. Even with the new technologies in the pipeline, weed control is going to be much more complex. The good old days of weed control with two or three shots of Roundup over the top are gone and are never coming back,” he said at the annual conference of the Mississippi Agricultural Consultants Association at Mississippi State University. “We’re just running herbicides into the ground one after another.”
Timely preemerge, postemerge applications important
What does work? A preemerge application that gets enough rainfall (or irrigation) for activation, followed by a timely postemerge application, Steckel says.
“You may or may not have to come back with a second postemerge application, depending on how quickly your beans grow and shade the ground. A high rate of Envive followed by Flexstar on 3-inch Palmer pigweed works well. Boundary, a premix of Dual and Sencor, followed by Flexstar, also works well.
“What I am worried about is that this weed will begin developing resistance to the herbicides we’re plugging holes with now, like Flexstar and Ignite. If that happens, we’re sunk. I don’t think growers realize just how close to the end of the rope we are on modes of action for this weed. It’s scary.”
For postemerge applications, he says, “Flexstar is my pick of the litter for 1-inch to 4-inch pigweeds. Cobra and Blazer don’t have the residual that Flexstar does, and 2-inch pigweed is about the cutoff for them. With LibertyLink beans, Prefix followed by Ignite on 1-inch to 3-inch pigweeds works well. Envive followed by Ignite works well on weeds up to 6 inches. Warrant is a new herbicide, comparable to Dual Magnum, that is labeled for postemergence in soybeans up to R3 and in cotton post-cotyledon to first flower.”
Another change growers need to make, Steckel says, is in spraying procedures. “We need to get away from AI sprayer tips and booms that are 5-feet above the ground, bouncing up and down, and going through the fields at 18 miles per hour with an 18 mph crosswind; that just is not ideal for effective coverage with contact herbicides like Flexstar, Ignite, or Gramoxone.”
In Tennessee, for marestail control, the primary recommendation is dicamba mixed either with glyphosate or Gramoxone, he says. Kixor, a burndown product that can be applied all the way up to planting.
“There are a host of preemerge materials — Valor-based products and Dual-based products do a pretty good job of residual for marestail and Palmer pigweed. Dual or other products as an early postemerge can give you overlapping residual when the preemerge is starting to play out.
“Once pigweed hits 2 inches, it can get away from you in a day’s time. I can’t stress strongly enough that it’s critical that you keep an eye on your fields so you’ll know if your preemerge is working and if you’re getting an overlap of residual.
“If you’re in an area that doesn’t have a lot of resistant Palmer pigweed, I’d at least put out a preemerge, if not an early postemerge — $12 or $13 worth of preemerge can be worth $30 to $50 the following year. Anything you can do to delay spread of this weed in your fields will be money ahead.”