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Turf MD: Why we need to remember the benefits of PGRs

By |  May 10, 2022 0 Comments
Karl Danneberger

Karl Danneberger, Ph.D

Thirty years ago, a new turf product was expected to have a significant impact on how we managed turfgrasses. I remember thinking, during the product’s pre-release stage, that it would most likely have a minor impact. Time proved me wrong.

Ironically, I recently saw some of myself in a cryptocurrency advertisement, where comedian Larry David misses out on major innovations throughout history, including — as the ad would have you believe — cryptocurrency.

That new turf product released in the early 1990s was Syngenta’s Primo (trinexapac-ethyl), a plant growth regulator (PGR). Prior to its release, we had several PGRs that were basically niche products. The PGRs available were:

  • Mefluidide (Embark). Used for Poa annua seedhead suppression.
  • Amidochlor (Limit). Targeted more for lawn turf suppression.
  • Paclobutrazol (ScottsTGR). Marketed as a Poa annua suppressor in creeping bentgrass fairways.

These compounds were often applied once or twice a year and had a specific purpose.

Broad Applications

Trinexapac-ethyl’s release changed how PGRs were used. We went from general products of one or two applications with a niche-type target to frequent, lower-rate applications with a broad range of plant health impacts beyond growth suppression. Currently, trinexapac-ethyl is the active ingredient in several generic products. The formulations, including Primo MAXX, have evolved considerably since the original formulations. Originally, trinexapac-ethyl was an emulsifiable concentrate (EC) or water-soluble bag (WSB) formulation. Cur- rent formulations, like Primo MAXX, have enhanced trinexapac-ethyl for ease of handling and safety.

Absorption Characteristic

Given that few turf products have been as researched as trinexapac-ethyl, I thought I would focus on just one trinexapac-ethyl characteristic. Trinexapac-ethyl is foliar absorbed. This absorption characteristic is im- important when compared to gibberellic acid inhibiting PGRs like paclobutrazol and flurprimidol. From published research, we know that the absorption into the leaf occurs around one hour after application.

Absorption time has practical im- importance because a significant rain event immediately after application would most likely result in a loss of product effectiveness. However, if that same rain event occurred 1 or 2 hours after application, little effect would occur. Paclobutrazol and flurprimidol are root-absorbed. Anuew (prohexadi-one-Ca) is foliar absorbed.

The absorption characteristic of the PGR may impact seed germination and establishment. Trinexapac-ethyl being foliar absorbed does not impact seed germination or seedling growth. The practical importance is with the winter overseeding of bermudagrass. A common practice in winter overseeding is to apply trinexapac-ethyl to bermudagrass one to two days or so prior to seeding. Trinexapac-ethyl slows bermudagrass growth but does not inhibit the cool-season turfgrass seed germination or growth at overseeding. Root-absorbed PGRs can reduce seed germination and suppress growth.

As a precaution, know the absorption characteristics when using a combination PGR product with gibberellic acid inhibitors.

As summertime temperatures rise, the length of growth suppression from trinexapac-ethyl decreases. One factor reported is the half-life of trinexapac-ethyl reduces as temperatures increase. From a management perspective, increasing the rate is less effective than reducing the application interval. First, retain the rate but shorten the interval to regain the expected growth suppression.

Above, I have mentioned a few of the characteristics of trinexapac-ethyl and, to a lesser extent, other gibberellic acid inhibitors. As an integral part of golf course management practices for such a long time, some benefits and uses are taken for granted or forgotten.

Fortunately, a comprehensive library of research exists on the benefits and characteristics of trinexapac-ethyl, all you have to do is search for it.

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