PGR effects on bacterial etiolation in bentgrass greens 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 in Raleigh, N.C., to evaluate the impact of plant growth regulators (PGRs) on etiolation of creeping bentgrass putting green turf. PGR treatments included trinexapac-ethyl applied at 0.044 lbs. a.i. per acre every seven or 14 days, or 0.087 lbs. a.i. per acre every 14 days; flurprimidol applied at 0.094 or 0.187 lbs. a.i per acre every seven or 14 days; and paclobutrazol applied at 0.062 or 0.125 lbs. a.i. per acre every seven or 14 days; and non-treated.

All treatments were applied from mid-April to mid-October in 2013 and from mid-April to late August in 2014. The entire plot area was inoculated with A. avenae for three 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 0.044 lbs. a.i. per acre every seven days and 0.087 lbs. a.i. per acre every 14 days had the most etiolation across both years. Trinexapac-ethyl applied at 0.044 lbs. a.i. per acre every 14 days has less etiolation than the same rate applied every seven days 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.

Joseph Roberts is a Ph.D. candidate, Jim Kerns, Ph.D., is a turfgrass pathologist and David Ritchie, Ph.D., is a plant pathologist at North Carolina State University. Roberts can be contacted at jarober3@ncsu.edu for more information.