Farm Progress

• It’s important to overlap pre-emergence treatments and chemistries by following a calendar rather than by driving out into the field to see if pigweeds are emerging.• When you come out to plant, you’ll think you have a clean field. But you won’t — the pigweeds are there.Growers shouldn’t be scared of resistant pigweed, they should just go after it.

Paul L. Hollis

January 24, 2011

7 Min Read

The first step is acceptance, and no, we’re not talking about a 12-step program. The name of this game is glyphosate-resistant Palmer amaranth pigweed, and the first step in preventing or battling it is admitting you have a problem.

“Don’t deny it, and don’t say that you’ve got only three or four on your farm, and you’re not going to do anything about it. It’s here and it’s real,” says Patrick Turnhage, a west Tennessee farmer. Turnhage was on a panel of consultants and growers telling of their experiences with resistant Palmer pigweed during a recent meeting in Decatur in north Alabama

Turnhage said it was great to see such a large turnout at the meeting focusing on resistant pigweed. “Five years ago, you couldn’t get two or three people together long enough to talk about it. If someone said resistant pigweed, they’d bust up like a covey of quail. You should treat a farm as if you cannot kill a pigweed. If it gets its head above ground and you treat it, but treat it as if you cannot kill it with anything, you’ll be successful,” he says.

It’s important, he says, to overlap pre-emergence treatments and chemistries by following a calendar rather than by driving out into the field to see if pigweeds are emerging.

“If that pre-emergence has a two-week residual, you need to get out in 10 days and spray. You’ve got to learn how to spray clean ground. It’s hard to do — it’s hard to spray something that is as clean as a concrete parking lot, but you’ve got to try and do it if you want to stay in business,” says Turnhage.

Resistant pigweed is putting farmers out of business, he adds. “We’re talking about bush hogging 80-acre cotton fields and disking up 1,000 acres at a time because they’d be alright,” he says.

Next July, says Turnhage, you can go to the foothills of Missouri, in west Tennessee, and tell exactly to the row where people have applied their pre-emergence, and where people are digging and trying to rescue their crop. “They’re spending more money trying to rescue it than they would have putting out the pre-emergence in a timely manner. My grandfather always said that you should spend money only on the things that make you money, and these pre-emergence treatments will make you money and keep you in business,” he says.

Turnhage farms about 5,000 acres of which approximately 3,000 will be planted in cotton this spring.

“We’ll actually put out herbicide before we do any tillage, because you can’t rely on tillage alone to eliminate that problem. Disking, bedding or chiseling alone won’t do the job. You have to kill pigweed before it gets above the ground.”

Turned off dry

Tunhage says he didn’t receive any significant rainfall after May 31 last year. “We might have received 1 3/10 inch until November — we were burnt up. If you take away the competition, and you’re spraying grass herbicides, the only thing that’ll survive is the resistant pigweed.

“If you’re doing a burndown, you may be using a 2,4-D and Dicamba combination, something with a long residual to get you to planting. When you come out to plant, you’ll think you have a clean field. But you won’t — the pigweeds are there. Spray that clean ground with Gramoxone, and put out another pre-emergence. If you have the capability, put out your herbicides before you disturb the ground. Put out herbicides in front of the planter and put out your pre-emergence behind the planter – it makes a huge difference.”

Tim Roberts, a consultant in west Tennessee and Missouri, says that when a cotton crop is emerged, if you don’t have WideStrike or LibertyLink, then there is no rescue treatment for Palmer amaranth resistant pigweed. “If you hood the middles with Gramoxone, you can try post-directed MSMA and Caparol on the row. We often have dry weather during planting time, but we’re getting pre-emergence out 2 weeks to 30 days ahead of planting, depending on if it’s Reflex or Valor, in the hopes of getting an activating rain prior to planting the crop. The pigweed in our area generally starts to come up at about the middle of April — about the time we plant cotton — and we’ll plant until the end of May.

“If you plant on May 10 and put out your pre-emergence, and then you have no activating rain, and you have an emergence of pigweed, you’re hurt. The way to counter that is to incorporate a yellow herbicide — which works pretty well — or apply an early pre-emergence, always with a burndown and something for marestail if that’s a problem. That should make you clean from the get-go. Then we layer our pre-emergence treatments,” says Roberts.

Growers shouldn’t be scared of resistant pigweed, he says, they should just go after it. “In 2009, we had 10 fields my group consulted on. We probably lost 10-percent yield from those fields due to resistant pigweed. We took an aggressive approach in 2010, and cleaned up the crop. We probably got about 95 percent control. We still had pigweeds in the field. Like boll weevils, you can clean them up, and you can manage them and make a crop,” says Roberts.

Resistant pigweeds can be moved by equipment, but they’ll also show up in the middle of a field, he says.

“Be proactive. We figure we’re spending about $37 per acre on resistant pigweeds, but it’s cheaper than attempting a rescue mission. Do your best to keep it from emerging. Your timeframe for getting control is narrow. The information about controlling resistant pigweed starts to sound repetitive after awhile, but keep listening,” says Roberts.

First noticed along waterways

John Newby, who farms in Alabama and Tennessee, says he first starting seeing pigweed up and down the river and along the creeks on his farms. “We first thought we didn’t have them. We thought maybe we didn’t get glyphosate on them because of the rain. But about four years ago, we decided we had them,” he says.

Pre-emergence herbicides have worked well, says Newby, and the yellow herbicides have been very effective.

“We’ve started putting out more liquid nitrogen, putting out the yellow herbicides, and then incorporating with a Turbo-Till, and that has worked really well for us. Once we get that down, we just keep hammering away at it. One thing we might have made a mistake on is that when we went with Flex, we pretty much threw our hoods in the garbage and didn’t do any layby or anything for awhile.

“But we started going back to that. We’ve taking advantage of the incentive program for hoods, and we try to do a better job with our layby,” he says.

Resistant Palmer pigweed is a “nightmare,” says Newby, and growers should do everything possible to stay ahead of it. “You’ll start out with a small spot. The next year, it’ll be as big as a pickup truck, and the next year it’ll be as big as a trailer. Once you get on it, don’t let up,” he says.

Bill Webster, a consultant in Alabama and Tennessee, says it was about four years ago when he decided he probably had a problem with resistant pigweed. “We had escapes that first year. Then, the next year — about three years ago —  we planted cotton, put down Prowl, let it get activated, came back twice with Roundup, and still had pigweed. We killed a few with Staple, but most of them survived and we ended up topping them out. The next year — two years ago — we planted in wheat and then came back with soybeans, double-cropped, and put out the pre-emergence,” he says.

When rain finally did arrive, says Webster, the pigweeds came up. “Once they get any size on them, you’re not going to get rid of them. This year, we noticed that the combines and other equipment spread them to more fields. You can tell where the equipment pulled into the field. There may be a streak of them or they may be scattered in the field,” he says.

Webster says he’ll be advising growers to do more incorporating of yellow herbicides. “We just need to stay on top of them. I don’t think we’ll ever eliminate them,” he says.

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About the Author(s)

Paul L. Hollis

Auburn University College of Agriculture

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