Effects of Plant Growth Regulators on Putting Green Aerification Recovery

Interim report - August 2021
Chas Schmid, Ph.D, Emily Braithwaite and Alec Kowalewski, Ph.D

Organic matter (OM) management with core cultivation is one of the most important management practices for golf course putting greens, and one of the most disruptive to golfers.  In northern climates, core cultivation is done in the spring and fall on actively growing cool-season turfgrasses to minimize improve recovery time.  However, this is also the time of year when golf courses experience the most play.  Thus, there is a need to reduce recovery time post-core cultivation to limit disruption to golfers.

Plant growth regulators (PGR) are commonly used on golf courses to manage vertical growth and to improve turf stand density.  Golf course managers apply PGRs routinely on a calendar-based schedule or using growing degree day (GDD) models (Krueser and Soldat, 2011) to limit post-inhibition growth enhancement (aka “rebound effect”).   In contrast, there has been a trend with sports field managers to use post-inhibition growth enhancement to recover from events that damage turfgrass, such as concerts (Polimer, 2020).  On golf courses, core cultivation is one of the most damaging events to occur, but no research currently exists that demonstrates the effect of PGRs on recovery from core cultivation, or if plant hormones such as gibberellic acid can be used to reduce recovery time.  

A pilot study was conducted by the authors at Oregon State University to investigate the effect of PGR applications on recovery time from core cultivation.  Preliminary results show that plots that received one spring application of trinexapac-ethyl (TE) 230 or 200 growing degree days (GDD) prior to core cultivation, reduced recovery time compared to plots that received two spring applications of TE which occurring just prior to core cultivation. These results suggest that TE applications just prior to cultivation slow the rate of turfgrass recovery, which is contrary to what most turfgrass managers assume.

A field study was initiated in March 2021 on a 1-yr old annual bluegrass putting green with the objectives to 1) determine the effect of trinexapac-ethyl application timing on core cultivation recovery, 2) determine if ethephon treatments influence cultivation recovery time, 3) evaluate the effect of gibberellic acid (GA3) on core cultivation recovery. Treatments were arranged as a 3 x 2 factorial with four replications.  Trinexapac-ethyl was applied up to either 400, 200, and 10 growing degree days (GDD) prior to cultivation, in combination with ethephon or no ethephon treatments. Gibberellic acid (RyzUp) applied at 1.4 and 2.8 g GA3 ha-1, and a non-treated control were included for comparison. Trial area was cored in the spring of 2021 with 1.3 cm inside diameter hollow tines in a 5.1 x 5.1 cm spacing. Following core cultivation, digital images were collected daily using a lightbox to determine percent cover over time.

Results from the spring of 2021 indicate that the main effect of ethephon treatments had the greatest effect on cultivation recovery time, with plots receiving ethephon recovering quicker than plots that received no ethephon (Fig. 1).  The main effect of TE timing was only significant on one date in the spring of 2021, where the last app of TE applied 400 GDD prior to cultivation had greater percent recovery 5-d after cultivation compared to TE applied 10 GDD prior to cultivation (Fig. 2).   Further research is needed to better understand how PGR applications influence cultivation recovery.

References:
Kreuser, W.C., and D.J. Soldat. A growing degree day model to schedule trinexapac-ethyl applications on Agrostis stolonifera golf greens. Crop Sci. 51:2228-2236.
Polimer, B. (2020). Why every sports field manager should consider using PGRs (SportsField Management). Retrieved from https://sportsfieldmanagementonline.com/2020/05/11/why-every-sports-field-manager-should-consider-using-pgrs/11506/

Figure 1. The main effect of ethephon (Proxy) treatment on core cultivation recovery (% recovery) of an annual bluegrass putting green turf in Corvallis, OR. 

Figure 2. The main effect of trinexapac-ethyl (Primo) timing (GDD prior to cultivation) on core cultivation recovery (% recovery) of an annual bluegrass putting green turf in Corvallis, OR.