Evaluation of the plant growth regulator Trinexapac-Ethyl (Primo Maxx) on Nordic golf courses

Outcome by 1 January 2009

The plant growth regulator Primo MAXX® (trinexapac-ethyl) offers prospects for reduced mowing costs, lower CO2 emissions, improved playing quality and better winter survival of turfgrass used for golf.  The main objective of this project is to provide documentation for potential registration of Primo MAXX® for use on Nordic golf courses.

The project started in 2007 with trials according to Good Experimental Practice standard at Landvik, Norway, and Lepaa, Finland. Primo MAXX® was applied at monthly rates varying from 0.2 to 0.8 L ha-1 on greens and 0.5 to 3.0 L ha-1 on fairways. These treatments resulted in average clipping yield reductions of 18% on bluegrass/fescue fairways and 21% on creeping bentgrass greens. Unfortunately, growth suppression during the first two weeks after application was often followed by a rebound effect during the remaining two weeks until next application. While significant losses in turfgrass quality occurred at rates 1.0 L ha-1 and higher in the fairway trial at Landvik, monthly applications of at least 1.5 L ha-1 ha resulted in significantly less snow mould (Microdochium nivale) and better overall appearance in the following spring in the green and fairway trials at Lepaa.
   
Because of the discoloration and rebound effects in 2007, Primo MAXX® was applied at lower rates but higher frequencies in new trials established in 2008. In a green trial at Landvik,  weekly or biweekly applications of 0.15, 0.30 and 0.45 L ha-1 were compared with an unsprayed check. On average for application rates and frequencies, Primo MAXX® had no effect on turfgrass overall appearance or density but reduced clipping yield by 25% and increased ball roll distance by 6%. In a new fairway trial at Lepaa, biweekly applications of 0.4, 0.8, 1.2 and 1.6 L ha-1 had no effect on turfgrass quality but reduced clipping yield by 15, 23, 23 and 34%, respectively. Rebound effects were virtually absent in the 2008 trials.

In conclusion, we consider these results sufficient to recommend Primo MAXX® being labelled for use on Nordic golf courses. As a starting point, we recommend the following rates and application frequencies to be printed on the label:

*Always use lowest rate for the first seasonal application of Primo MAXX®.

STERF would like to emphasize that any use of Primo MAXX  on golf courses in the Nordic countries must await official approval by national authorities.