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Reversing resistant-pigweed problem

Two years ago, only days after several fields had been sprayed with glyphosate to control pigweeds, Sid Fogg surveyed his acreage and wondered how the pest was still thriving.

“At first, I thought my spray guy had done a poor job,” says Fogg, who has farmed in east Arkansas’ St. Francis County since 1977. “The pigweeds weren’t dying and I thought they were misses.”

Then, in 2009, Fogg harvested wheat in early June and planted soybeans. When the soybeans came up, “pigweeds were solid. We sprayed like we had been for years and it just didn’t work. That meant we had a complete disaster on about 400 acres of wheat-beans.”

At that point, it was obvious, says Fogg, “We had to do something different.”

Two words

Asked what farmers are calling him about this growing season, Bob Scott, Arkansas Extension weed specialist, says, “Two words: Palmer pigweed. Soybean calls are mostly on pigweed.

“The unfortunate thing is the calls now are on 8- to 10-inch pigweed in Roundup Ready varieties. And for that circumstance there’s no good answer.”

Such uncertainty is “tough on weed scientists because you want to give a producer a good solution when he calls. You’d think, in 2010, we’d have an answer for every weed situation. But for 10-inch Palmer pigweed, I recommend a 1.25-pint application of Flexstar. That will provide only about 60 percent control. You’ll burn them back. And, right now, there’s a lot of products being sold that’ll burn a pigweed. But they’ll be back in short order.”

Some are employing mechanical means to combat the weeds.

“A lot of guys are cultivating. That’ll take out a few pigweeds and it’s better than nothing. But you can only get so close to the row and it’s not providing the level of control that’s needed.

“Hoe crews are more common in cotton since it’s a higher-value crop. There aren’t many hoe crews in soybeans.”

With the surge of resistant weeds in the Mid-South, Scott sometimes finds it difficult not to be “all gloom-and-doom. But remember what I’m hearing every day. No one calls me when Roundup works, when Valor and Prefix are activated, when Flexstar GT went out early and the fields are clean. I get calls when things don’t work.”

And the news isn’t all bad. “There are clean fields out there and we’ve seen a tremendous increase in the use of residual herbicides — a 100 percent increase in their use every year for the last three years.”


Having been “on-point with the weed resistance issue” for years, Scott and colleagues have not only talked about weed resistance but also dealt with it in real-world scenarios. While planning for a 2010 project, “we wanted to have a centrally-located pigweed-affected operation to work with.”

Then, late last fall, Scott was called to Fogg’s Widener, Ark., operation.

At the time, Fogg “was about ready to pull his hair out because he’d done just about everything he could think to control the pigweeds and nothing worked,” says Scott. “He was behind from the beginning of the season and wasn’t able to catch up.”

It turns out the farm’s pigweed is not only glyphosate-resistant but also ALS-resistant. “That means, besides glyphosate, products like Classic, Synchrony and Scepter won’t kill the pigweed. There are severe limitations on what will actually work on the farm’s pigweed.

“So, in our initial discussions last year it became obvious something drastic had to be done. He couldn’t keep on doing the same thing because he was losing money on the worst pigweed fields.”

The weed scientists and Fogg agreed to work together to solve the pigweed conundrum. Thus far, it has been a successful collaboration


“Specifically, we took control of a 70-acre field along with a small, 20-acre triangle-shaped field,” says Scott. “These were two of the worst pigweed fields — dryland and completely infested.”

The 70-acre field was divided in half, one side planted in LibertyLink varieties and the other in Roundup Ready varieties.

“We have tried to provide both sides with the best possible weed control programs we could come up with,” says Scott. “We did make a few concessions to make it a bit easier for him to farm — but only minor things.”

The results have “proven to be pretty amazing. It’s almost a night and day difference — and he’s spent about the same amount of money to get the fields clean. That isn’t to say it has been cheap. The words ‘pigweed’ and ‘cheap’ don’t hold hands, right now. But getting pigweed control is critical if you want to make beans.”

As for the triangle field, “we took about 10 acres and set up around 12 research plots. Those include many different programs in both Roundup Ready and LibertyLink varieties. There are some excellent examples that show how to approach weed control in those crops.

“The number one thing we’ve learned is no matter what technology you go with, weed control’s success or failure hinges around the first two weeks at planting time. If you get pre-activated, if you get the first post shot out within seven to 10 days after emergence, you’ll be in a successful program. Anything we’ve done short of two shots of Ignite hasn’t worked.

“So, we’ve learned more about earliness and how to use residuals and reinforced things we already knew. And we’ve shown the best ways to use the new LibertyLink technology.”

Fogg agrees. Since the demonstration began, “things have looked great. What they’ve accomplished is fantastic.”

Answers in plots

Anyone with a pigweed problem needs to attend the June 29 field day showcasing what’s been done in Fogg’s fields. Answers to a myriad of resistant weed management problems can be found in the plot work.

Directions to resistant pigweed field day

From I-40 take exit 247 and travel south on Hwy. 38 for 2.1 miles to Widener, Ark. Cross the railroad track and keep going straight onto South Jefferson/SFC 713. Continue on SFC 713 (road continues on top of levee) for 3.5 miles. Turn left (east) onto SFC 774 for about 0.6 miles. At the Chappell Farm sign take SFC 728 (left) for about 1.4 miles. GPS coordinates are 90⁰38’54”w/34⁰58’32”n. For more information, contact county agent Mitch Crow at (870) 261-1730 or e-mail

“I encourage farmers to come see what these scientists are doing here,” says Fogg. “It’s worth the time and effort. You can learn what chemicals will, or won’t, kill resistant pigweed.”

Fogg says he now has the knowledge to deal with the weeds. “Chemicals alone won’t solve things. The timing, rains, the lack of rain, wind blowing towards a vulnerable crop — all factor in. Even with all the knowledge, unfortunately, it doesn’t always work. Almost all the (viable) chemicals have to be incorporated with a rain.”

Fogg still has fields with emerged pigweeds “where we did everything correctly — except for doing it in a timely fashion. You have to be timely. We knew to put out a pre-emerge and we did. But it was two weeks before it rained so it wasn’t incorporated. That meant the weeds came up.”

Included in the Fogg plots are salvage programs.

“The pigweed population is so heavy that there have been multiple flushes,” says Scott. “Even some of the better programs have a few pigweeds. That just shows how tough it is to achieve a clean field.”

Scott and fellow weed specialist Ken Smith “felt it was important and valuable to get out and do this work on an actual farm with a variety of environments. It has some irrigation, some dryland, different soil types — all the trials and tribulations that farmers have to deal with. We’re trying to work through the season hand-in-hand with the farmer.

“I’ve certainly learned a tremendous amount about doing all of this in a timely manner. It’s a good Extension story to tell.”

Many have already gone through the plots and the field day “will be highly educational for growers. It’s something where a grower can view the different plots and programs and say ‘hey, this can work for my farm’ or ‘no, this is too much trouble.’ The options are there for the farmer to consider.”


TAGS: Soybean
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