Increasing rates of the current and a new formulation of Primo MAXX for plant growth regulation on greens and fairways


Syngenta’s plant growth regulator Primo MAXX® (trinexapac-ethyl, 121 g L-1), was registered in Sweden in Aug. 2011 and in Finland in 2013. Syngenta has also developed a new formulation with approximately the same concentration of active ingredient (115.3 g L-1) but with different additives/filling agents. The two formulations were compared at increasing rates to green and fairway in green and fairway trials in Norway and Finland in 2013. 

The four trials showed only minor differences in efficacy or safety between the two formulations. In some cases, the new formulation had a slightly stronger growth-regulating effect than the old formulation, but differences were not statistically significant. It was therefore concluded that the new formulation can replace the old one, or the two formulations can be used interchangeably at the same rates.

In the fairway trials, reductions in turf visual quality with increasing rates of both formulations occurred after the first application and during a dry period in July and early August. Among the negative aspects were more red thread disease and increased competition from broadleaved weeds. These responses were more conspicuous on a fescue/colonial bentgrass-dominated fairway than on a Kentucky bluegrass-dominated fairway on a more fertile soil. It is recommended that the initial rate of Primo MAXX® on fairways be limited to 1.0-1.2 L ha-1, but  the rate can be increased as greenkeepers gain more experience on their own course.

Compared with the unsprayed control, clipping reductions in the green trials varied from 15-20% at rates 0.2 and 0.4 L ha-1 to approximately 30% at 0.8 L ha-1. Regardless of formulation, the treated turf was always significantly darker than the untreated control. Initial applications of 0.8 L ha-1 reduced the visual quality, but the creeping bentgrass greens needed less time than the fescue-dominated fairways to accustom to the PGR. It is concluded that both Primo MAXX® and the new formulation should be labelled with ‘0.2 L ha-1 every week or 0.4 L ha-1 every second week’ as standard application rates for Nordic golf greens.

In 2014, the findings from this and earlier projects were compiled into a handbook on the use of Primo MAXX® on Nordic golf courses. The handbook also includes a summary of practical experiences from Swedish greenkeepers using Primo MAXX® in 2012 and 2013. English, Swedish and Norwegian versions of the handbook are available on the STERF website. 

All activities in this project were carried out under the Industrial Partnership Agreement between STERF and Syngenta.

Category: Overwintering
Status: Finished
Project period: May 2013 - September 2014

Fundings (kSEK)













Other sources1)












1)The project is funded by Syngenta and carried out according to the Contract Service Evaluation Agreement between STERF and Syngenta.

Project objectives

  • To determine optimal rates for Primo MAXX® and a new formulation of trinexapac-ethyl for application on green and fairway
  • To summarise results and practical experiences on the use of Primo MAXX® on Nordic golf courses into a handbook.

Project participants

Ingunn M. Vågen

Norwegian Institute for Bioeconomy Research (NIBIO), Section for Urban Greening and Environmental Technology. Landvik, Reddalsveien 215, 4886 Grimstad

+47 40622904

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