The perception that all hard red wheat varieties respond equally to plant growth regulators doesn’t hold up in the field, according to an Alberta Agriculture and Forestry researcher.
“We’ve looked at several different hard reds that have a height reduction, but they don’t have the improvement in standability that we need,” Dr. Sheri Strydhorst told farmers at Saskatoon’s CropSphere in January. Strydhorst and her family also have a grain farm near Neerlandia, Alta.
Strydhorst’s research revealed varieties responded differently to Manipulator, a newly registered plant growth regulator, even when they were part of the same class.
Strydhorst also debunked the idea that plant growth regulators (PGRs) such as Manipulator will always work on tall cultivars and never work on short ones. Those hard and fast rules may not be “a complete version of the truth,” she said.
“So I think we really need to do our homework here.”
How PGRs work
To understand the inconsistent response to PGRs, it’s important to understand how the products work, Strydhorst said. PGRs affect hormonal activity within the plant. They reduce the rate of cell elongation, keeping plants shorter and stronger, Strydhorst explained. They also decrease the cell division rate, she added.
“They’re effective at low concentrations and they break down rapidly, which has some pluses and minuses.”
One potential minus is shoot elongation. Manipulator inactivates the hormone gibberellin, shortening the plant. But because Manipulator breaks down quickly, all that inactive gibberellin can become active.
After the plant “sees a whole flush of gibberellin” it can end up taller, she said.
Other potential side effects include unproductive tillers and short-term height drops that don’t last until harvest, she added.
Staging is critical with PGRs, Strydhorst said.
“If you’re using something to make your crop shorter, if you apply it at the wrong stage, you could get yield decreases.” The crop safety window for Manipulator is fairly wide. But the efficacy window for can be anywhere from 24 hours to three days, depending on growing conditions, she said.
PGR labels also warn against applying product while the crop is under stress. But the tolerance level for stress is a question mark. Strydhorst said they were measuring soil moisture and canopy humidity during their PGR trials to fill in that blank.
Researchers looked at variety response to Manipulator at eight different sites in Alberta.
They grew varieties under either standard or advanced management. Standard management meant no extra nitrogen, no PGR and no fungicide. Advanced management plots received an extra 34 kg of nitrogen per hectare, Manipulator at the label rate, and two fungicide applications.
Researchers rated how each variety lodged, under both standard and advanced management. A rating of zero meant no crop lodging, while 100 meant it was entirely flat.
Strydhorst presented data from 2014 and 2015. She said the irrigated Lethbridge site in 2015 was a “nice textbook” case for looking at Manipulator’s effect on wheat crops. (Data from this site is shown in the table.)
Strydhorst said Manipulator consistently reduced the height and lodging of AC Harvest. “So textbook, that works how it’s supposed to.”
The GP varieties saw a height reduction with Manipulator, but the untreated checks didn’t lodge. “These cultivars seem to be able to stand even through wet snows in early September. So this is an example where you get a height reduction, but you don’t need the PGR to help this crop to stand.”
Coleman and Thorsby saw height drops with Manipulator, but they still lodged, Strydhorst said. “You might be able to shorten them, but you’re not going to make them stand.”
Strydhorst and her colleagues also looked at PGRs’ effects on Foremost wheat, a CPS variety commonly grown in Alberta.
Strydhorst presented two years of research results from five sites ranging from an irrigated site near Lethbridge to a site in the Peace. Researchers have one more year left in the study, which will ultimately give them 15 site years of data.
Researchers applied Manipulator and an unregistered PBR to the plots. Manipulator-treated wheat consistently yielded less than the control. The other PGR yielded higher in seven out of 10 sites. Two of those higher yields were statistically significant.
Strydhorst cautioned that Manipulator’s yield drops weren’t statistically significant, and the data was preliminary. It’s also worth noting that Manipulator doesn’t claim to boost yield.
“What’s concerning me is that although we have non-significance, we have a downwards trend with the Manipulator seven out of 10 site years. That trend just makes me a little nervous,” she said.
But when it came to reducing plant height, Manipulator delivered. It reduced plant height anywhere between one and eight cm, and the average drop was 4.8 cm. The other PGR was inconsistent, and sometimes made plants taller, Strydhorst said.
Researchers also saw an eight-bushel yield drop with the second PGR in Bon Accord in 2015.
“I’m sure there was heat stress. I’m sure there was drought stress. You shouldn’t put these on at 30 C, but we were coming out of the growth stage that it needed to go on within,” said Strydhorst.
Protein response was another area to watch. Strydhorst only had 2014 protein data available, but she noted a significant protein drop on Manipulator-treated wheat compared to the untreated control, in two out of five sites. The other PGR-treated wheat saw a statistically significant protein drop at one site.
While the protein data was preliminary, the trend is “on the radar as something we need to watch,” Strydhorst said. She noted the protein problem vanished with a fungicide application.
Asked whether she would use a PGR on her own farm, Strydhorst said it would be a “case-by-case scenario.”
“If I’m growing Foremost, and I’m not selling that into the U.S., and I’m pushing my fertility to 120 lbs. of nitrogen, and I think I’ve got good soil moisture in the spring, yes I will use a PGR,” she said.
“But I’m going to make sure that I get that staging right. And I’m going to also make sure that I have good moisture. If it’s stressed at that time, I’m not going to use it.”
Strydhorst’s entire presentation is online at cropsphere.com.