Grower changes strategy to control pigweed

Managing 8,500 acres of row crop land is tough enough when everything works the way it’s supposed to work. When your herbicide won’t work on your toughest to manage weed — there is a big problem.

Rowland, N.C., grower Roger Oxendine knows all to well how the above scenario plays out. He says he has some level of glyphosate resistant weeds on most, if not all, of his 8,500 acre operation.

That’s a problem, he states matter-of-factly. Pigweed, crop yield, crop quality and most of all pickers and combines simply can’t be efficient in competition with pigweed. Controlling pigweed in a glyphosate resistant world has caused Oxendine to change his management strategy in all his crops — even the ones in which pigweed, glyphosate-resistant or not, is not a problem.

Oxendine farms in a partnership with his brother on some of the land that was first farmed by his grandfather. Roger and his brother took over the farming operation from their father and have been at it now over 30 years.

Like so many farmers, no-till and Roundup ready crops made it possible for the Oxendines to greatly expand their farming operation. They now grow crops on about 8,500 acres in the south-central part of North Carolina — not much more than a stone’s throw from the South Carolina line.

They currently grow more than 600 acres of tobacco, 5,500 acres of soybeans (most of it double-cropped with wheat), 1,600 acres of corn, and 3,000 acres of wheat.

Until recently the Oxendines were among North Carolina’s largest cotton producers. Glyphosate resistant pigweed, he says with a grin, was just one of many reasons they got out of the cotton business.

“We grow so many acres of tobacco, and cotton and tobacco just don’t work out well for us. Both are labor intensive, and labor is hard to find and keep, and the dollar return on cotton just wasn’t there for us — not the last few years we grew it,” Oxendine says.

“We got out of cotton in 2004, with much of that land going into soybeans. We noticed some Palmer pigweed in some of the old cotton fields in 2005, but we didn’t really associate that with glyphosate resistance,” he adds.

In 2006, he says, it was obvious he was dealing with pigweed that was resistant to some of the herbicides he was using. “On some farms it wasn’t a problem at all, but on other farms it was a really serious problem.”

“Once we talked to other people and weed specialists, and anyone we could find to ask about these weeds, we realized we had glyphosate resistant weeds. At that time glyphosate resistant pigweed was so new that there was not much information as to how to manage it.”

“Now that we understand the significance and the scope of the problem, we have changed around our whole farming operation to better manage the problem,” he says. He explains they changed some of the crops they were growing, cotton in particular. They also changed the timing, method of application and different modes of action of herbicides they use in all their crops to address the problems they had in most of the fields in which they had previously grown cotton and/or cotton and soybeans.

Glyphosate resistant weeds started out in small clumps, sometimes streaks in soybeans, he says — by that time they no longer grew cotton. The first year (2005) they sprayed some fields three times with glyphosate and the resistant weeds predictably got bigger and bigger.

One of the common problems with glyphosate resistant pigweed is that spraying them with glyphosate eliminates most of the other weed and grass competition and gives the fast growing pigweed a good growth environment. The result is very predictable — five-six foot tall Palmer pigweed that are 6-7 inches in diameter at the base of the plant by the time the crop matures.

“Early on in the process, we combined some of those fields with mature pigweed, and there is no doubt we unknowingly spread resistant seed from field to field over our entire farming operation,” Oxendine says.

At about the same time the North Carolina farmers began noticing difficult to control pigweed in their soybean fields, they likewise began to see increased weed problems in their tobacco fields.

“We were just beginning to get information about glyphosate resistant pigweed, but we didn’t use glyphosate in tobacco. We used Prowl and Command as the primary herbicides in tobacco. Now, we know we had both glyphosate and ALS (acetolactate synthase)-inhibiting resistant weeds,” Oxendine says.

One of the first things the North Carolina farmer did to manage resistant pigweed was add Prefix to his herbicide program, primarily in soybeans. Prefix is a combination of long chain fatty acid chemistry — the family of herbicides that includes Dual-Magnum and a PPO herbicide.

So far no weeds have been documented to have resistance to the long chain fatty acid chemistry. The protoporphyrinogen oxidase-inhibiting (PPO) family of herbicides likewise has no documented resistance problem, but is more prone to develop these problems, if it is over-used over a long period of time.

By applying this two-family herbicide punch to pigweed early in the season growers get two different modes of action and can usually clean up pigweed before it has a chance to go to seed. Regardless of whether it is glyphosate resistant or not, eliminating mature Palmer pigweed from a field is a big advantage.

“We had used Dual for years behind our planters. It was helping to control pigweed, but we needed something in addition, especially in fields where we knew glyphosate wouldn’t work. On one 700 acre field in particular, we used Prefix on part of the field and it was like night and day on Palmer pigweed control,” Oxendine says.

He explains that using the combination of herbicide families for two consecutive years in that particular field has essentially eliminated Palmer pigweed problems.

“In our soybeans, we put down a quart of Prefix per acre right behind the planter. That gives us a two to three week window of control. Then, we come back early with glyphosate. We used to wait until pigweeds were 10-12 inches tall, thinking we were doing the right thing to wait until all the weeds had germinated. Now we know the secret is to come back as quick as we can and clean up the field before the weeds have a chance to get started,” he adds.

If Prefix doesn’t completely kill the weed, it weakens even the glyphosate resistant pigweed enough that glyphosate will usually kill it. Plus, by that time, there is more crop competition that helps manage weed growth, he says.

“We now spend close to $20 per acre more for herbicides than we did back when we could come in with one application of glyphosate tank-mixed with some other herbicides to get specific weeds,” Oxendine says.

With the price of glyphosate more than triple in price in some areas this year compared to the 2007 cropping season, combined with higher use rates, the gap in price between a glyphosate monoculture and a multi-family herbicide program may not be so great.

“We do a better job of cleaning our combines and other field equipment. We do a better job of scouting weeds. And, we know more about different herbicide chemistries and how they work under different conditions. “Every year is a slightly different animal when it comes to weed control, so staying current on herbicides is more critical when you have herbicide resistant weeds,” Oxendine says.

“There is no doubt that glyphosate resistant pigweed is a problem, but it is a problem that farmers can manage. It takes more management, especially staying on top of weed development and spraying in a timely manner. And, it costs more money, but managing herbicide resistant weeds can be done,” he adds.

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