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82 GOLF COURSE MANAGEMENT 07.14 drought onset compared to 2011. Each main plot of drought was divided into replicated subplots that were treated with Primo Maxx (trinexapac-ethyl, Syngenta Pro - fessional Products), glycine betaine or Primo Maxx + glycine betaine. In 2010 and 2011, Primo Maxx was applied twice, biweekly dur - ing the month of May (May 17 and 31, 2010; May 16 and 30, 2011) as per manufacturer- recommended rates for creeping bentgrass turfgrass at 10.9 fuid ounces/acre (0.8 liter/ hectare) Primo Maxx (0.25 fuid ounce/gallon [1.95 milliliters/liter] [v/v]; a.i. trinexapac-ethyl = 11.3%). Glycine betaine (200 millimoles/ liter) was applied weekly four times over the 31-day dry-down period in 2010 (June 1, 8, 15, 22) and seven times over the 48-day dry-down period in 2011 (May 31; June 7, 14, 21, 28; July 5, 12). The carrier volume was 87.12 gallons/ acre (815 liters/hectare) applied with a pressur - ized (40 pounds/square inch [276 kilopacsals]) backpack sprayer. The concentration of glycine betaine used was chosen based on a preliminary test that showed positive effects on creeping bentgrass growth at the 200 millimoles/liter concentration in a growth chamber study. Results and discussion Creeping bentgrass performance measured as visual turf quality (on a scale of 1-9, where 1 is dead, brown grass and 9 is best-quality turf ) based on color, density and uniformity dur - ing drought stress was signifcantly improved by the sequential application of Primo Maxx before drought stress and glycine betaine dur - ing drought stress in 2010 and 2011 (Figure 1). Turf treated with Primo Maxx alone also maintained higher water content during early drought stress, but the effectiveness dimin - ished following prolonged periods of drought stress in both years (Figure 2). The effects of Primo Maxx on improved turf performance were mainly due to increases in the amount of green leaves or canopy density (Figure 2). Glycine betaine applied singly during drought stress resulted in signifcantly higher visual turf quality (Figure 1) and leaf water content (Figure 3), but did not have signif - cant effects on the canopy density (Figure 2) in both years. The improvement in drought tolerance by the application of glycine betaine was mainly due to enhanced water retention and suppressed leaf dehydration. Turf treated with glycine betaine appeared to be brighter green with more active growth rather than dull green with ceased growth as seen in the Turf was mowed weekly at a height of 0.4 inch (10 millimeters) with clippings removed and watered three times per week to maintain soil water content at feld capacity (30%) before the drought treatment. The soil type was a Nixon sandy loam (fne-loamy, mixed, semi - active, mesic typic hapludults). Emerald fungicide (boscalid, BASF) was applied at the manufacturer's recommended rate of 7.8 ounces/acre (548.9 grams/hectare) in late April to preventively control dollar spot disease before trinexapac-ethyl application. Urea (46-0-0) was also applied in late April at 24 ounces nitrogen/1,000 square feet [7.3 grams/square meter] to promote spring green- up. No fungicides or fertility were applied dur - ing the experimental period of 2010 or 2011 to avoid confounding effects. After the study was terminated in 2010, the feld was again treated to control dollar spot and a spoon-feeding fer - tility regimen was implemented to deliver 8 ounces nitrogen/1,000 square feet (2.4 grams/ square meter) every two weeks until the grow - ing season ended. In 2010, irrigation was withheld for 31 days. In 2011, irrigation was withheld for 48 days. The duration of drought differed be - tween years due to weather conditions. The 2010 trial experienced hotter days with more wind during the drought period, causing rapid Figure 3. Leaf relative water content under well-watered control and drought stress in 2010 (A) and 2011 (B) for plants treated with Primo Maxx (PM only + drought), glycine betaine (GB only + drought), and Primo Maxx plus glycine betaine (PM + GB + drought). Vertical bars indicate LSD (least signifcant difference) values (P ≤ 0.05) for comparison between treatments at a given day of treatment where signifcant differences were detected. Leaf relative water content 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 A. 2010 PM-only + drought PM + GB + drought GB-only + drought Untreated drought control Well-watered control Days of drought stress Relative water content (%) 0 5 10 15 20 25 30 35 B. 2011 PM-only + drought PM + GB + drought GB-only + drought Untreated drought control Well-watered control Days of drought stress Relative water content (%) 0 10 20 30 40 50 080-089_July14_TechwellCuttingEdge copy.indd 82 6/17/14 2:32 PM