Biostimulant and Plant Growth Regulator Effects On Etiolation of Creeping Bentgrass Putting Green Turf.

Etiolation of creeping bentgrass has recently emerged as a significant problem on golf course putting green turf.  Recent reports have incited multiple bacteria (Acidovorax avenae and Xanthomonas translucens) as causal agents of etiolation, but little is known on how biostimulant and plant growth regulator (PGR) applications influence this condition.  In 2011, field and greenhouse research trials were initiated to evaluate the impact of biostimulants and the PGR, trinexapac-ethyl, on etiolation caused by A. avenae and X. translucens.  Biostimulants (Astron, BioMax, CytoGro, Knife Plus, Nitrozyme, Perk Up, and non-treated) and trinexapac-ethyl were selected based on the frequency of applications observed with etiolation samples submitted to the NC State University Turf Disease Clinic.  Treatments applied at label rates were arranged as a split-plot, randomized complete block design with biostimulants (14 d interval) as the main plot and trinexapac-ethyl (7 d, 14 d, and none) as the sub plot.  Etiolation developed naturally in the fall of 2011 and X. translucens was frequently isolated.  In 2011, biostimulants did not influence etiolation development; however, trinexapac-ethyl applied 7 d and 14 d significantly reduced etiolation, regardless of biostimulant factor.  Treatments were altered in 2012 and 2013 to obtain more replications.  Etiolation was slow to develop in 2012 and 2013 so plots were inoculated with A. avenae by applying a cell suspension (10⁸ cfu ml^-1 in H₂O) to the foliage.  During summer 2012 and 2013, biostimulants did not have a significant impact on etiolation; however, trinexapac-ethyl, applied both 7 d and 14 d increased etiolation compared to none, regardless of biostimulant factor.  Additional greenhouse trials are ongoing to evaluate the impact of biostimulant and PGRs on etiolation caused by A. avenae and X. translucens.