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Soybeans — resistant weeds, treatments, LibertyLink

The storm arrived at Dee Henderson’s farm east of Keo, Ark., just as a tour of LibertyLink soybean plots and treatments began. Even as lightning flashed and thunder boomed in the downpour (which, a few minutes earlier, had set the record in Little Rock for most rain in a July) the large crowd was able to see eye-opening plot work in a field infested with glyphosate-resistant pigweeds.

Those in the field “pulled out a few umbrellas and/or got soaked as we hurriedly walked out of the 17-treatment test,” said Bob Scott, Arkansas Extension weed specialist and Delta Farm Press contributor. “I thought it was a bit of a testament to how this pest has got their attention.”

A few minutes later, buckets of rain still falling, everyone took shelter under Henderson’s shop where the “tour” continued.

“I want to highlight a couple of things about the plots,” said Scott. “First of all, those plots were not an example of a severe infestation of Roundup Ready- or glyphosate-resistant pigweeds. That is a fairly inconsistent, light infestation.”

Producers in east Arkansas’ Lee and St. Francis counties “know what a severe infestation is. Over there, we’re seeing carpets. I was in Randolph County and saw a field that was an absolute carpet of glyphosate-resistant pigweed.”

The populations of resistant weeds vary around the state. “But they’re everywhere and still popping up.”

Despite the proliferation of glyphosate-resistant weeds, because of seed availability and the way Mid-South agriculture is set up, “we’ll still be growing Roundup Ready soybeans. So, we must address this problem. Whether you’re growing Roundup Ready beans, trying LibertyLink beans or are going back to conventional beans, pigweed is one of the main things we must deal with.”

Early, early, early

When addressing resistant pigweed, the current buzzword from weed specialists is “earliness.”

“Early, early, early,” repeated Scott. “‘Early’ meaning pre-emergence herbicides; pre-emergence herbicides in with your burndown, and pre-emergence herbicides following the planter. We must rethink how we farm soybeans. We must accept the fact that we have pigweeds that glyphosate won’t take out anymore and earliness” is paramount.

Herbicides used in the test plots the crowd had been chased from had every chance to impress. The plots received a “six-tenths of an inch rain immediately following the test plot-applied pre-emergence herbicides. We saw the best possible out of those pre-emergence herbicides.”

If a grower gets in a situation where pre-emergence herbicides don’t work, earliness becomes even more critical.

“Whether you’re coming back with Flexstar in Roundup Ready beans or Ignite in LibertyLink beans, you must be early. UltraBlazer on quarter-inch-tall pigweeds is a good treatment, as well.”

Scott is “very confident” that a full rate of Flexstar or FlexstarGT will control up to a three-inch-tall pigweed.

“Ford (Baldwin, weed scientist/consultant/Delta Farm Press contributor) tells me to say a quarter-inch-tall pigweed and that’ll help everyone catch them early enough. When the field turns a bit purple with pigweed, hit it.”

Researchers have found it’s too late for Flexstar “when you miss the pigweeds with Roundup WeatherMax, then up the rate and hit it again when they’re knee-high. At that point, Flexstar will just burn the pigweeds some.”

Arkansas farmers must “go back to scouting beans, back to program approaches in beans and paying more attention to what the fields look like from year to year and anticipating what we need to use for the following season.”

Good residuals

There are many good residual herbicides available.

“The only two new tools we have are Valor and Prefix as pre-emergence tools. Everything else is as it was when I started working in Arkansas with American Cyanamid in 1997. There’s been nothing new in terms of pigweed control since then, which was about the time Scepter stopped working.”

As a result, Mid-South agriculture was “so grateful” to have Roundup Ready beans come along. And “we’ve utilized the technology — over-utilized it, as it turns out in some cases — since. I’m seeing problem fields all over the state.”

What about application volume, coverage and droplet spectrum?

Scott warned that glyphosate stands alone among herbicides. One of the great things about glyphosate is a single drop on a leaf will translocate. It has good surfactants and will move in and kill the plant.

“You can make a fairly uneven, somewhat sloppy application and still have a very clean field at the end of the year.”

That isn’t the case with Flexstar or Ignite.

“We’re going to have to rethink applications. That means we’re getting into dangerous territory when creating smaller droplets. That isn’t as big a concern with Flexstar as it is with Ignite, as it’s a non-selective.”

In general, “we want better coverage and a few more ‘fines’ and mid-range droplet size.”

As for air induction tips, “it’ll be trial and error in the field to see if they work. In general, high water volumes will work better with Flexstar and Ignite.”

Unfortunately, drift remains a concern and will necessitate “a steep learning curve. We’ve been trying to answer the question about Ignite drift. Small amounts of Ignite drift on rice won’t cause the same damage as Roundup. Get a lot on rice and it will cause a problem. So I won’t tell you it’s safe to drift Ignite on rice. By no means is that true.”

Asked for high points of the Henderson farm plots, Scott pointed to:

• LibertyLink soybeans

“Any pre-emergence herbicide followed by Liberty was mostly pigweed free. The best ones were Valor or Prefix followed by Ignite twice, however the sequential Ignite looked pretty good with no pre, Ignite plus Dual early followed by Ignite also looked good.”

• Roundup ready will still work

However, “you need a pre-emergence herbicide followed by a postemergence herbicide. Valor or Dual followed by a very early shot of Flexstar GT (Flextstar plus glyphosate) looked good.”

What about low points?

“It’s depressing to look at two shots of glyphosate or Roundup and see about 70 percent pigweed control.”


TAGS: Soybeans
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