Farm Progress

• Everyone probably should not be using the same program.When you look at the yield data, there’s not a statistical difference in yield between the recommend postemergence treatments.

Paul L. Hollis

May 20, 2013

6 Min Read
<p> POST-HARVEST CONTROL is an important component of controlling troublesome corn weeds such as glyphosate-resistant Palmer amaranth pigweed and tropical spiderwort.</p>

Georgia corn producers have several good options for herbicide programs, but Extension Weed Scientist Eric Prostko says that if he was king for a day, he’d require one thing.

“If you had to do at least one thing that I say, I would tell you to spray a quart of atrazine at planting, for a couple of reasons,” says Prostko.

“If we use a quart at planting, that would allow us to use 1.5 over-the-top, and that gives us the maximum legal amount of atrazine we can use in corn.”

Another reason he cites is time savings. “One of your most precious commodities is time, and the ability to get into the field on a timely basis. If we use a quart of atrazine at planting and it gets activated, it’s likely we’ll get very good control of pigweed. It buys you time to make a postemergence application. You might need to tend to other crops, or you might have bad weather.

“We all know he key to postemergence applications is timeliness,” he says.

For most corn producers in Georgia, it boils down to one or two products, says Prostko, including atrazine plus glyphosate or Roundup Ready, Liberty Link, Steadfast Q, Laudis or Capreno or Halex 6T, which is glyphosate, Callisto and Dual.

 “All of these are very good products that do a very good job on the weed species we have.

With all of our recommended programs, we see very good control of the targeted weed species, especially of pigweed. I’m always asked which program works the best, and which one growers should be using.

“Everyone probably should not be using the same program. When you look at the yield data, there’s not a statistical difference in yield between the recommend postemergence treatments.

“One program may be better than another in certain situations, but it generally doesn’t translate into yield. All these programs are very good, as long as we’re getting them out in a timely fashion,” he says.

Many corn producers become concerned, says Prostko, when their plants turn yellow from early herbicide applications.

Plant damage?

“When you first get a look at the field, you may have some concerns about the injuries you see on the plants. But when we take those plants to yield, even where we had injury, we really didn’t see any difference in yield, so I’m still very confident that the herbicide treatments we’re using aren’t doing any undue harm.”

Many growers now are making 250-plus bushel corn yields, he says, but researchers haven’t been able to duplicate that in trials for a couple of reasons, including irrigation and rotation issues.

“But we’re getting better. There are a lot of stresses when growing a crop, including heat, insects and diseases. Where you’ve got higher yields and you’re managing all the stresses you can, you start to wonder if herbicides are doing something to affect those yields.

“We’ll continue looking at this in the future, especially in on-farm tests, to make sure we’re not putting any undue stress on the plants with herbicides.”

There are a few new products on the market this year, including Zidua, marketed by BASF, says Prostko.

“It’s an 85 WG formulation with a primary ingredient of pyroxasulfone. We can use it preplant incorporated, pre-emergence or early postemergence. It provides residual control of annual grasses and certain broadleaf weeds, including pigweed.

“It doesn’t bring a new mode-of-action to the table, being the same as Dual or Warrant, but at lower rates. An advantage is that it’s a lower-use-rate material of 1 to 2.75 ounces per acre.”

FMC will be marketing the same ingredient — pyroxasulfone — in two products, Anthem and Anthem ATZ. Anthem is Cadet and Zidua, and Cadet does have postemergence activity, he says. Anthem ATZ contains atrazine.

“Everyone is talking about 2,4-D and dicamba-resistant technology in cotton. The 2,4-D technology also will be available in corn. In fact in 2013, Dow will launch its Enlist herbicide-resistant corn in the Midwest. These are corn hybrids that have enhanced tolerance to 2,4-D.

“We could use 2,4-D in conventional corn, but we were restricted in terms of rates and time of application. This technology allows for higher rates and more flexibility in the timing of applications.

“We can go to a later application date without causing any yield problems. The biggest issue for us will be off-target movement of the herbicides.”

Prostko reminds growers that once they get corn out of the field, their work isn’t done regarding glyphosate-resistant Palmer amaranth pigweed.

“We would like to see you implement a fall program for the management of Palmer amaranth pigweed. This could include several things, including tillage. We need to control the fall population and prevent it from producing seed.”

Researchers have spent a lot of time in the last seven years or so focusing on controlling Palmer amaranth in all crops, he says.

Tropical spiderwort

“But this past year, I probably got as many questions on tropical spiderwort as I did on Palmer amaranth. We need to make sure tropical spiderwort doesn’t come back and cause us more problems.

“Most tropical spiderwort doesn’t come up until later in the season, especially if you planted early. If you planted in February or March, your herbicides will probably be effective until June.

“Aim or 2,4-D postemergence work very well on tropical spiderwort, and Sequence plus atrazine or Expert works well in Roundup Ready corn. Aim, Gramoxone or Evik plus Dual is effective at layby.”

What growers do after harvest for tropical spiderwort might be even more important than what they do in-season, says Prostko.

“We can use tillage or two applications of 2,4-D, Gramoxone or Aim. When most of the spiderwort comes up, it’s past the point to where it will influence your yields.”

The other bane to corn growers’ existence is morningglory, he says.

“I wish I could tell you we had the answer, but because of where we farm, we’ll always be battling morningglory. Our crop comes up so early, and the sunlight gets through the canopy early, so nothing really lasts for the full length of our growing season.

“That’s why you should use as much atrazine as possible, some at planting and some at early postemergence.”

Other herbicides that work on morningglory include 2,4-D, Clarity, Status, Aim and ET, he says.

“We could tank-mix those with glyphosate if we needed to. Liberty is a lot more effective on morningglory than glyphosate. It’s even possible to consider getting the corn out of the field early, before morningglory becomes too much of a problem.”

Prostko advises corn producers to be vigilant in rotating chemistries with different modes of action.

“Most farmers in Georgia grow multiple crops, and in the last two years we’ve seen a significant increase in the use of Dual and Warrant, and now there’s Zidua.

“These are great products, but they all have the same mode of action. Watch how you use these products. If you don’t, you could create resistance problems with this mode of action.

“We don’t have it yet, and we want to keep it that way. If you’re rotating these products, it doesn’t mean you’re rotating modes of action.”

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About the Author(s)

Paul L. Hollis

Auburn University College of Agriculture

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