4/3/2020 - By Dr. Jeff Atkinson

During these crazy times, and with the current Executive Order for golf courses to perform minimal maintenance, we have received quite a few calls and questions regarding plant growth regulators (PGR). Below are six considerations for PGR use on greens, tees, fairways, and roughs:

1. All active ingredients are not the same. Many plant growth regulators share a similar mode of action; however, the amount of regulation each PGR provides will vary between turf types. Consult manufacturer labels for suggested application rates and turf safety.
2. Know the product irrigation requirement prior to application. Cutless (flurprimidol) and Trimmit (paclobutrazol) should be irrigated within 24 hours following application. These products are mainly root absorbed. Anuew (prohexadione calcium), Primo MAXX (trinexapac-ethyl) and Proxy (ethephon) are foliar absorbed and should be allowed to dry on the leaf surface following application. Combination products such as Legacy (flurprimidol + trinexapac-ethyl) and Musketeer (flurprimidol + paclobutrazol + trinexapac-ethyl) should be allowed to dry on the leaf surface for a minimum of 1 hour to allow for trinexapac-ethyl absorption, then irrigated within 24 hours.
3. Consider scheduling applications using growing degree day (GDD) intervals while labor is limited to increase program efficiency. Growing degree days is a simple calculation which sums the average daily air temperature over a period of days and weeks. Once the sum reaches a threshold value, the PGR should be reapplied. This simple equation accounts for and helps to mitigate the commonly observed phenomenon wherein the duration of PGR effects is reduced during periods of elevated temperatures. PGR application scheduling is made easy by using the GreenKeeper App.
4. Understand the difference between longevity and intensity of growth regulation. Much of the research conducted in the last decade aimed to better quantify the influence of PGR application on turf growth. One interesting finding is that higher rates result in a higher intensity of growth regulation, but not necessarily a longer duration. If a longer duration is desired, consider a PGR with a longer growing degree day (GDD) application interval.
5. Consider tank mixing with other products to enhance labor efficiency. Foliar absorbed products can be combined with foliar absorbed PGRs. Root absorbed products can be combined with root absorbed PGRs. Conduct a jar-test for all product combinations that you do not have previous experience with.
6. Consider PGRs for areas other than large-acreage turf areas. They can also be successfully utilized around bunkers, sprinkler heads, curb edges and even for ornamentals.

PGR Options

These products can all provide effective growth control, but please reach out to your Harrell's rep for specific rate, interval and application questions for your property. Grass types, timing and budgets can all play a factor in which strategy will fit best for each situation.