Make decisions on your PGR program based on how your course’s turf is actually growing rather than having a set program all year-round.
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Plant growth regulators (PGRs) are useful components of a turf management program and offer significant benefits. The turf becomes greener, texture improves, and leaf density and stress tolerance increase. In addition, the plant requires less nutrient to thrive.

But if used improperly, PGRs may not deliver the desired result and may cease to be cost effective. Here are a few steps for superintendents to get the most out of their PGR of choice — and their budget.

Have an Objective

It’s important to have a clear idea of what a PGR program needs to achieve, says Dr. Dean Mosdell, a technical manager for Syngenta.

“What’s the objective of your PGR program?” Mosdell says. “Are you trying to regulate growth? Are you trying to improve playing conditions? Are you trying to differentially suppress one grass over another, Poa control or Poa suppression, for example? Have an objective and design your program around the best way to meet that objective.”

Choose the Right PGR

Superintendents must choose a PGR that is appropriate for their particular facility, says Dr. Bill Kreuser, assistant professor of agronomy and horticulture at University of Nebraska-Lincoln. “If you have a lot of annual bluegrass or you have ultradwarf Bermudagrass greens, you’re pretty much limited to Primo and Anuew,” he says. “If you have (cool-season grasses) then the Class B PGRs – Cutless and Trimmit – and the combos come into play.”

Conduct a trial with a PGR before committing to it, Mosdell says. “Just like any other plant protection product, the superintendent should probably trial the material first and see what response they’re getting. Are they seeing the clipping reduction they’re looking for? Are they seeing the color and the density?”

The choice of product should be determined in large measure by the program objective, says Dr. Zac Reicher of Bayer’s Greens Solutions Team. “If you’re after annual bluegrass seedheads, that’s Proxy. That’s a no-brainer,” he says. “If you’re after annual bluegrass management, that’s either Trimmit or Cutless. If you’re after growth regulation, clippings, things like that usually that’s either Anuew or Primo, but then sometimes Cutless, Trimmit and Legacy also work.”

Don’t Jump the Gun

Superintendents, to their credit, are often anxious to implement a program at the start of the season. But Mosdell says holding off a bit may be more beneficial in the long run.

Don’t start too early when the grass isn’t growing actively, he says. And you may want to start with a lower rate in the spring because spring could be late and you could have variability in temperature. It could get really warm and then get cold for a while.

“A good indication as to the amount of growth is the clippings you’re getting in the baskets,” Mosdell says. “That’s an indication of (proper) PGR rate and frequency.

“The same thing in the fall. If you get an early fall and growth slows down, and you can see that change in clipping production, that’s an indication you may want to skip an application or reduce your rates. Obviously, you want to stop applications in the fall as we head into the cooler times of the year.”

“If you’re under applying, you’re pretty much wasting money because as soon as the PGR wears off, all that growth suppression you’re going to get back and it’s actually going to rebound. The grass will actually grow faster than grass that wasn’t treated.” — Dr. Bill Kreuser

Determine the Appropriate Application Rate and Intervals

It’s not uncommon for superintendents to apply too much or two little PGR, Kreuser says. “If you’re under applying, you’re pretty much wasting money because as soon as the PGR wears off, all that growth suppression you’re going to get back and it’s actually going to rebound,” he says. “The grass will actually grow faster than grass that wasn’t treated.”

So, if you under apply, or apply too infrequently, the turf bounces back and forth and it’s undo stress on the turf. “While it’s not a huge concern, it’s kind of inefficient” he says.

On the other hand, applying too much PGR can also lead to difficulties, Kreuser says. “That’s going to arise in two different ways,” he says. “One, we don’t look at our growing-degree day accumulations. So, we’re not timing our applications based on how fast the PGR (is being absorbed).

“So, if it’s cold in the spring, you’re applying the PGR faster than the plant can break it down,” he adds. “It’s kind of a stacking effect. You’re applying it faster can either have it mowed off or it breaks down.”

The other way it happens is the intervals are much shorter on greens, Kreuser says. “They’re mowed more frequently, they’re mowed shorter than the collars,” he says. “So, when you’re spraying the greens, you’re over spraying the collars. Even though the interval might be appropriate for the green and it’s promoting good plant health, the collars are getting over applied while the greens are doing just fine.”

As a result, with the traffic on them and mechanical damage and poor soil and irrigation coverage the collars start to die, Kreuser says.

Some superintendents determine their application rate by the calendar; making weekly or biweekly applications at a low rate, Mosdell says. “Maybe you’ll want to follow a regular schedule,” he says. “But if you’re not getting any clipping production, you may want to skip a week. To me it always comes down to clippings and how the grass is growing.”

“I talk to a lot of superintendents who are using low enough rates or they’ve figured out a system,” Reicher says. “They’ve been doing it for long enough that they somehow can use the calendar very well.

“There are so many ways to skin this cat. There’s lots of art to this science, so far be it from me to judge the guys who are doing it right by the calendar,” he adds. “But by and large, most of the guys now are going toward some aspect of growing degree days.”

Be Careful of Green Collars

As mentioned above, green collars are often at risk from what might be termed an overdose of a PGR, simply because collars don’t require as heavy an application as the putting surface itself.

The majority of the collar decline Reicher sees is caused by PGRs. “When you move (off the green) out into the collars and even first cuts of rough, you run into different species or different mowing heights,” he says. “And those growth regulators will be more active or potentially more injurious with higher mowing heights.

“A great example of that is if they’re using Trimmit, which is great for controlling and minimizing annual bluegrass. If you take that into the collar at a higher height of cut, you end up with what superintendents here in Nebraska (where Reicher is based) proudly call The Ring of Fire; the turf turns yellow.”

Use Caution When Increasing Green Speeds

PGRs are an effective tool for superintendents in search of faster greens (or whose members are demanding them), but Reicher says it’s possible to go too far.

He sees superintendents pushing greens so far that growth is virtually stopped. “And I understand, part of it is labor management, part of it is green-speed management,” he says. “But the last time I checked, these grasses still have to grow to recover from ball marks and traffic.”

Reicher has worked in the turf industry for more than three decades. He notes that over the course of his career he has increasingly seen superintendents lower mowing heights in response to the pressure to produce faster green speeds.

“It makes for a lot of sleepless nights for superintendents.” Reicher says. “When I started this, they were mowing greens at a quarter-of-an-inch. It was a lot easier to manage grass back in those days. Some guys now are down near 1/10 inch,” he says. “A lot of guys are still at 1/8 inch and some guys who are using aggressive growth regulators are a little bit higher than that.”

Adjust When Necessary

All competent superintendents are adept at making adjustments on the fly and Mosdell emphasizes that should be the case when it comes to a PGR program. “I always recommend not having one program all year-round,” he says. “Make adjustments based on what you see, if it’s color, if it’s clipping production. Make decisions on your PGR program based on how the turf is actually growing rather than having a set program all year round.” Rick Woelfel is a Philadelphia-based turf writer and frequent GCI contributor