Golfdom, April 2016

Super Science Continued from page 31 example the Primo Maxx label allows for application rates ranging from 55 to 11 fl oz acre 0125 to 0250 fl oz 1000 ft2 Figure 2 shows how much theoretical Primo Maxx is in the turf plant based on real weather data from our research station in Nebraska The red line indicates the low rate and the green line indicates the high rate of Primo Maxx in the plant The white line is the critical amount of PGR required to suppress growth Notice how the big differences in Primo Maxx quantity quickly decay and begin to converge together at the white critical point line Also notice that the Primo Maxx quantity decays faster in June than May because it was cooler in late May Its clear why increasing application rate has a minimal impact on PGR longevity Its more important to apply more frequently at two halflives to maintain growth suppression The half life concept also explains how applying PGRs too frequently can lead to an accumulation of active ingredient in the plant tissue even at low application rates Lets tweak the thought experiment from the previous paragraph Instead of three Primo Maxx application rates well re apply the 55 fl oz acre rate every 100 200 or 300 GDD one two or three half lives The 200 and 300 GDD intervals causes the amount of Primo Maxx in the plant to increase to roughly 55 oz acre immediately after application but the Primo Maxx in the 300 GDD interval drops below the critical value Figure 3 This interval doesnt sustain growth suppression The 100 GDD interval does the opposite That interval causes the amount of Primo Maxx to increase in the plant After a couple re application cycles the amount of Primo Maxx in the turf is double the amount that would be in the plant if it were re applied every 200 GDD two half lives Figure 3 This happens because Primo Maxx is being applied FIGURE 2 12 10 8 6 4 2 0 5 May Theoretical Primo Maxx in the turf fl oz acre The impact of application rate on the longevity of Primo Maxx in a cool season putting green outside Mead Neb The dashed yellow line represents the critical level where growth suppression starts to wane FIGURE 3 20 18 16 14 12 10 8 6 4 2 0 5 5 15 Theoretical Primo Maxx in the turf fl oz acre 55 fl oz acre 83 fl oz acre 11 fl oz acre 10 May 15 May 20 May 25 May 30 May 4 Jun 9 Jun 14 Jun 19 Jun 3 Half Life 300GDD 2 Half Life 200GDD 1 Half Life 100GDD 5 8 15 5 11 15 5 14 15 5 17 15 5 20 15 5 23 15 5 26 15 5 29 15 6 1 15 6 4 15 6 7 15 The influence of re application interval on the amount of Primo Maxx in a coolseason putting green outside Mead Neb Re applying every two half lives maintains consistent levels of Primo while the three half life interval doesnt sustain sufficient Primo Maxx to sustain suppression and the one half life interval leads to Primo accumulation in the plant This can result in deep growth suppression and the potential for over regulation 32 Golfdom April 2016 Golfdom com