Page 24 - GreenMaster summer 2023
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A study by Dr. Bill Kreuser at the University of Nebraska-Lincoln suggested that the ideal re- application interval for most PGR treatments (using trinexapac-ethyl) is from 270–310 GDD, and resulted in the recommendation of application of trinexapac-ethyl every 200 GDD for creeping bentgrass greens. This research was performed to show the efficacy on prohexadione-calcium using a GDD schedule and 300 was chosen to see if the less frequent application was ideal.
EXPERIMENT DETAILS
The trials in Guelph evaluated turfgrass growth and quality parameters on a mature bentgrass/ annual bluegrass greens height stand, on a constructed ‘California’ style putting green. The experiment began on May 25, 2021, with pre- treatment fertilizer application and ended on August 24, 2021, with the final clipping collection and visual ratings.
The greens area was maintained at ~3 mm height of cut, mowed five times weekly. Regular mowing was skipped to allow 4–5 days of growth prior to clipping collections. The plots were brushed prior to clipping collections to remove dew and to stand the turf up, which improves sample collection. The turfgrass colour and quality was rated on 1–9 scale, canopy reflectance (normalized difference vegetation index, NDVI) was measured using a Greenseeker optical sensor, and clippings were collected using a Toro Greensmaster Flex-18 walk behind greens reel type mower.
THE RESULTS
Happily, no stress symptoms (yellowing or etiolation) were seen in response to the PGR treatments during hot/dry weather at any point during the experiment and the PGRs significantly reduced turfgrass growth when compared to the untreated control. The NDVI ratings with the Greenseeker were unable to differentiate the treatments, but
Dry Clipping Weights (g)
Jun6 Jun15 Jun24 Jun28 Jul5 Jul9 Jul14 Jul26 Jul30 Aug3 Aug11 Aug16 Aug20 Aug24
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visual turf quality ratings ranked the PGR treatments as good, or better, than the untreated control.
When comparing the 300 GDD and 4-week application schedules for trinexapac-ethyl and the experi- mental product, the 4-week spacing treatments resulted in 4 applications between June 4 and August 16, whereas the GDD schedule recom- mended 6 applications in the same time frame. On three of the rating dates, the calendar spray resulted in higher clipping weight than the GDD schedule and on two rating dates it was the opposite (see graph above). Not surprisingly, the clipping weight was affected by the duration since last application, which means that the 4-week schedule resulted in more clippings (thus more growth) over the entire experiment.
Dry weight of turf clippings for PGRtreatmentsappliedona300GDD (Jun4,Jun21,Jul6,Jul21,Aug6)or 4-week schedule (Jun 4, Jun 29, Jul 26, Aug 16). Significant differences between the application schedules are indicated with red and green arrows.
The experimental product performed similarly to Primo on both application schedules and often was ranked the same for many parameters
throughout the experiment. Since other products with the same active ingredient are currently on the market, Nufarm has put the registration of this experimental on hold.
Based on this, and experiments at other locations, Anuew was registered by Nufarm in May 2022, and it is now on the market to improve turf quality and clipping suppression.
RECOMMENDATIONS
• PGRs containing prohexadione- calcium or trinexapac-ethyl can suppress turf growth to reduce mowing frequency.
• Trinexapac-ethyl can be mixed with prohexadione-calcium if the former alone is not providing enough control.
• Use a growing degree days schedule for PGR application to ensure consistent growth suppression.
•300 GDD seems to be a good threshold for prohexadione calcium applications based on experiments in southern Ontario – Note: this may not apply to all regions of Canada where nighttime temperatures can influence GDD greatly. GM
