Project status January 2014
The plant growth regulator Primo MAXX (PM, active ingredient trinexapac-ethyl) inhibits the last step in plant synthesis of GA1, the bioactive form of the plant hormone gibberellic acid. Because PM is not persistent in plant tissue, it has to be reapplied at regular intervals to have a consistent effect on cell elongation and turfgrass clipping yields. If application intervals become too long, turf treated with PM will rebound, i.e. grow faster than the untreated turf. Research in Wisconsin, USA, has shown that the duration of growth suppression depends on temperature, and that optimal application interval in the northern US (40-49ºN) is 200 GDD (growing degrees days with base temperature 0 ºC).
The Nordic countries are located at 56-71ºN and the maximum day length at midsummer ranges from 18 to 24 h. For grasses native to the Nordic countries, it is well documented that the long summer days have a strong impact on leaf elongation, and that this effect is mediated by GA1. For northerly adapted grasses, the rebound effect can therefore be expected to occur faster in the Nordic countries than at lower latitudes. Adding to this is the fact that temperatures are generally lower.
This project was conducted under the industrial partnership programme between STERF and Syngenta. We studied the effect of increasing temperature and photoperiod on duration of growth suppression, measured in GDD, after application of PM (0.8 or 1.6 L/ha to creeping bentgrass (Agrostis stolonifera), maintained at 10 mm mowing height, in growth chambers at the Bioforsk Særheim from 20 Aug. to 30 Sept. 2013. All pots received 10 h of fluorescent light (269 μmol/m2/s1) and day length extension was provided by low-intensity incandescent light (2.2 μmol/m2/s1). On average for 11 clippings during the fiveweek period after application, the two rates of PM reduced DM production by 24 and 43 %, respectively. Increasing day length from 10 to 15 and 20 h increased DM production by 5 and 28 %, respectively, but the interaction between Primo Maxx and day length was not significant. By fitting cubic polynomials to the data, it was found that the duration of growth suppression after application of Primo Maxx, expressed in GDD, is longer at high than at low application rates and longer at high than at low temperatures. The likely implication of this is that the optimal GDD between Primo Maxx applications is lower in the Nordic countries than in the US, but this has to be verified by experiments under natural daylight conditions.