Growth regulators lessen lodging

Plots of Gadsby barley at Barrhead, Alta., show the results of Manipulator, chlormequat chloride, on the left and Moddus, trinexapac-ethyl,  on the right, with treatments applied at growth stage 31-32.  |  Sheri Strydhorst photo

Barley growers riding the fine line between big crops and big headaches have some new tools in the form of plant growth regulators (PGRs) to reduce lodging.

“I would say that anywhere where growers are toying with that 80 to 100 bushel per acre for yield, they are likely suffering lodging,” said Sheri Strydhorst, agronomy research specialist with the Alberta Wheat Commission and Alberta Barley.

PGRs work by interfering with a plant hormone called gibberellin, which tells plant cells to grow and elongate, lengthening the stem of the plant. Strydhorst explained that until recently, only one PGR, Ethrel, had been used for barley, but its approval for the crop has been withdrawn.

This changed for the 2020 growing season when the approval of Manipulator (chlormequat chloride) was expanded from wheat to include barley and oats. Another option for 2021 is Moddus (trinexapac-ethyl). But which one works better?

Strydhorst said international research from 2015 onward shows Moddus gets a better response from barley than Manipulator, as do 15 site years of Agriculture Canada data from across Western Canada. She also did her own comparisons at Barrhead northwest of Edmonton, on Synergy and CDC Copeland barleys.

“We found Manipulator reduced plant height by three centimetres and Moddus by 10 centimetres,” she said. “We didn’t have a lot of lodging in the trial, but when we did, we found the Moddus improved standability.”

“I think all the signs from international, Western Canada and more locally from me at least, show that Moddus is the PGR of choice for use on barley.”

Strydhorst hastened to add that this is not a strike against Manipulator.

“Moddus, it’s great on barley, but that doesn’t mean Manipulator doesn’t work on wheat. It does.”

As to where to use a PGR, Strydhorst said they are likely most useful in black soil zones with plentiful natural moisture or irrigation.

“It’s in these highly productive areas because the varieties we have for barley just don’t have the standability.”

Adding a PGR means adding cost, both for the product itself and the extra pass with the sprayer over the field. Strydhorst said that while both Manipulator and Moddus can piggyback with herbicides and fungicides in a tank mix, getting the timing right — at the 30 to 32 growth stage — usually means PGRs must be applied with a dedicated pass.

“If you’re going to spend the money and do this, it’s going at growth stage 30 to 32 when there’s no other pass needed over the field.” Strydhorst said. This means, roughly, that for barley seeded in early May, the window for PGR application will be early June.

A critical consideration, particularly for the 2021 growing season, is moisture.

“We have certainly seen yield reductions, when we have drought conditions,” Strydhorst said. “That’s very real and the labels both clearly state don’t use it when your crop is environmentally stressed or under drought. So I think drought equals no PGR.”

Strydhorst also cautions that barley growers should follow the Keep it Clean guidelines regarding crop protection products. In particular, they should check with their buyers before applying Manipulator, since some customers for food, feed, and malt barley do not allow it.

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