Plant Growth Regulator Effects on Etiolation Development in Creeping Bentgrass Putting Green Turf Caused By Acidovorax Avenae.

Bacterial etiolation, an unusual elongation and chlorosis of turfgrass stems and leaves, has developed into a predominant concern among turfgrass superintendents managing creeping bentgrass (Agrostis stolonifera L.) putting green turf.  Recent research has shown that bacteria, Acidovorax avenae and Xanthomonas translucens, are causal agents.  In 2013, a research trial was established at the Lake Wheeler Turfgrass Research facility in Raleigh, NC to evaluate the impact of plant growth regulators on etiolation of creeping bentgrass putting green turf.  Plant growth regulator treatments included trinexapac-ethyl applied at 0.049 kg ha^-1 every 7 or 14 d, or 0.098 kg ha^-1 every 14 d, flurprimidol applied at 0.105 or 0.210 kg a.i. ha^-1, paclobutrazol applied at 0.070 or 0.140 kg a.i. ha^-1, and non-treated.  All treatments were applied from mid-April to mid-October in 2013 and from mid-April to late August in 2014 to plots arranged in a randomized complete block design with 4 replications.  The entire plot area was inoculated with A. avenae for 3 consecutive nights by applying a bacterial suspension (~10⁸ colony forming units ml^-1) to freshly cut turf and covering with a permeable cover overnight to encourage infection.  Inoculation was performed in mid-June 2013 and early June, early July, and early August in 2014.  Percent turf area exhibiting etiolation was rated periodically throughout both seasons using a grid count method and while etiolation was observed throughout both seasons, bacterial decline did not occur.  Trinexapac-ethyl applied at 0.049 kg a.i. ha^-1 every 7 d and 0.098 kg a.i. ha^-1 every 14 d had the most etiolation across both seasons.  Trinexapac-ethyl applied at 0.049 kg a.i. ha^-1 every 14 d has less etiolation than the same rate applied every 7 d on 6 of 15 rating dates across both seasons.  Flurprimidol and paclobutrazol at both rates had significantly less etiolation and were typically no different than the non-treated control.  Although trinexapac-ethyl treatments were associated with more etiolation, these plots also exhibited the best turf quality.