Features Cereals
PGR potential in intensively managed systems

Does it make sense to apply a plant growth regulator (PGR) in winter cereals?

A newly released study analyzing the effects of dose and application timings of the PGR trinexapac-ethyl (sold under the trade name Moddus in Canada) on lodging, yield and quality of winter cereals suggests there’s a role for trinexapac-ethyl (TE) in some systems.

Brian Beres, a senior research scientist in agronomy for Agriculture and Agri-Food Canada (AAFC), led the study, which ran between 2014 and 2017 at six locations in Western Canada.

At the time, Beres says, there was a lot of interest in winter wheat, and in the tall hard red winter wheat variety Moats. During the scale-up of Moats pedigreed seed prior to its launch, some seed growers reported problems with lodging. Prairie-wide, growers were experiencing very good growing conditions and high yield potential, which can test the straw strength of cereal crops, Beres says.

Beres wanted to look at a PGR that was ready to use right away in winter cereals, and TE was showing promise in terms of application window flexibility and crop safety.

But he didn’t want to confine the project just to Moats. “I was interested in an array of winter cereals, from winter wheat to a fall rye, because of the range in height differentials and subsequent potential for lodging. Fall rye (Hazlet) is quite tall, [and] Moats is a taller winter wheat that has potential to lodge. [And] what happens to a reduced-height winter wheat when treated with a PGR?”

Study design and results

The study ran in Lethbridge, Kipp and Lacombe, Alta., Melfort, Sask., and Brandon, Man. over four growing seasons. TE treatments were applied to two winter wheat cultivars, Moats and Flourish, an early-maturing, reduced-height hard red winter wheat variety, and the fall rye cultivar Hazlet.

Application of TE reduced plant height of all cultivars used in the study, but timing and dose responses varied. Physical reduction in height was greatest for Hazlet, but Moats saw the greatest reduction in height as a percentage of overall height, at 8.2 per cent (versus five per cent for Hazlet).

Beres found that there was flexibility with timing, but the results suggested crop response was more consistent at a full dose. If applied at a full dose, TE was effective at mitigating lodging in all treatments.

Despite the lodging complaints Beres had heard about Moats, he didn’t observe the same level of severity in the study plots.

All treatments, except an early application at a low dose, increased yield compared with the controls, with highest yields for Hazlet. “Compared with the control, application of TE improved grain yield by 3.0 to 7.9 per cent for Hazlet, and 3.0 to 3.4 per cent for Moats, which tended to be optimized at the 0.6 times or [the] full dose applied at Feekes 7,” writes Beres in his publication on the study, adding that similar studies by different authors corroborate these findings.

“Even in conditions absent of stem lodging, or that only promoted the crop to lean over a little, we still observed a significant increase in grain yield,” he says. “Not only does that possibly provide a threshold to pay for the application, but it gives you the confidence that even if you don’t have conditions to allow for lodging, it’ll shorten that crop and take what it’s gaining in carbon and partition that into grain production, or reproductive parts.”

Agronomic considerations

PGRs, like pesticide and herbicide inputs, aren’t cheap. Beres says they likely have greatest application in intensively managed systems under irrigation.

TE is a useful management tool that can be “stacked” into such a system, he says.

But other management tools should be considered first. The first is to select the best genetics, and then to “position that variety to exploit the potential it offers,” Beres says. Producers should also consider the seed lot, seeding rates, and strengths and limitations of their rotations, as well as how tightly they’ve “dialed in” their N management systems, before deploying a PGR, he says. Water and nitrogen are the greatest yield-limiting factors for cereals.

“If it’s an environment that will facilitate an intensively managed approach and there’s a risk of lodging, I think it’s a valuable tool and it’ll probably provide the returns, given the value of wheat going forward for at least the short term,” he says. “And they can probably expect some kind of a yield bump in the range of three to eight per cent, and a reduction in plant height of up to 10 per cent.”

Sheri Strydhorst is an agronomy research specialist for Alberta Wheat and Barley Commissions. She says besides TE, there is one other PGR registered for use on winter wheat in Western Canada, chlormequat chloride (Manipulator 620). In Eastern Canada, ethephon (Ethrel) is registered for use on winter wheat.

Producers can find information on PGRs in Alberta’s Crop Protection Guide, the Alberta Blue Book.

Alberta Wheat and Barley has also released a PGR staging video on YouTube under the title “Growing Smarter: plant growth regulator staging for wheat and barley.”

In the video, Strydhorst walks producers through optimal PGR application timing for both wheat and barley with products such as trinexapac-ethyl and chlormequat chloride, and other agronomic considerations.