Daren Bohannan, Bayer CropScience tech services representative, notes the characteristics of Palmer amaranth in a soybean plot during the “Respect the Rotation” tour near Essex, Ill.
Daren Bohannan, Bayer CropScience tech services representative, notes the characteristics of Palmer amaranth in a soybean plot during the “Respect the Rotation” tour near Essex, Ill.
ESSEX, Ill. — University weed specialists have spread the word the past few years about Palmer amaranth and how its move northward will be a game-changer in weed management strategies.

Game on.

Existence of the “frankenweed” has been confirmed in nearly 30 counties throughout central, northeast and southern Illinois, and more than one-third of those counties had glyphosate-resistant Palmer amaranth.

The potentially devastating weed was the focus of a Bayer CropScience “Respect the Rotation” tour at a Kankakee County field research site.

Palmer amaranth is a summer annual broadleaf weed species related to other pigweed species — waterhemp, smooth and redroot — common in Illinois.

Research has demonstrated that Palmer amaranth has a higher growth rate and is more competitive than other pigweed species.

Growth rates approaching three inches per day and yield losses of 78 percent in soybeans and 91 percent in corn attributed to Palmer amaranth have been reported in the scientific literature.

The female plants can produce hundreds of thousands of seeds per plant, and once the plant has grown to four or more inches, the effectiveness of herbicide treatments dramatically drops.

As is the case with its waterhemp cousin, Palmer amaranth is capable of developing resistance against a variety of herbicides, and the greatest likelihood for successful control is an integrated management approach.

The need to “Respect the Rotation” is evident in controlling the fast-growing and difficult-to-control Palmer amaranth, and the field tour featured the weed’s prodigious growth and/or control with the use of various herbicides.

Research Collaboration

Daren Bohannan, Bayer CropScience tech services representative, said the “Respect the Rotation” is an initiative the company began about six years ago to elevate the importance and grower adoption of herbicide diversity.

“It’s an initiative to collaborate with universities, establish research on existing biotypes of resistance weeds and to basically give us a platform which to work with these universities, rent ground and do research on the three Rs, which are rotate modes of action, rotate crops, and rotate herbicide-tolerant traits,” he said.

“We bring the universities into these sites to do work, we encourage them to approach the other chemistry manufacturers, make sure that they’re represented and we can work together and come up with solutions.”

This marked the first year at the Kankakee County site.

“Up until last year no one was aware that Palmer amaranth was growing in this area. We started looking at this and found that it wasn’t (herbicide) resistant waterhemp it is Palmer,” Bohannan said.

Soybean and cotton growers in the southern U.S. have become the unwilling and unfortunate case study in the expansion of herbicide-resistant Palmer amaranth.

High Control Costs

Larry Steckel, University of Tennessee row crop weed specialist, said at the tour it is a costly weed to control.

From 2006 to 2014, herbicide costs to control these resistant weeds in cotton have risen from $60 an acre to $100 to $120 per acre, University of Tennessee studies show.

“For soybeans using Roundup, we’re at $80 to $100 an acre, and we were at $30 per acre,” Steckel said. “It’s increased our cost in corn to $60 to $70 per acre, and it used to be $30.”

Steckel said one farmer in Tennessee collected data that showed from 2006 to 2012 his fertilizer cost increased 48 percent, seed cost increased 50 percent and his herbicide cost went up 250 percent in that same timeframe.

“The good news is we’re able to control it. We’re spraying a lot, and we also have chopping crews going out that at $20 to $25 per acre on top of these herbicides,” he said.

“The thing that’s concerned me is these commodity prices are not so great any more and you start to really wonder about sustainability.”