The USGA and concerned golf courses supported university studies of an unusual problem on bentgrass greens. Symptoms often coincided with changing weather conditions and were more prevalent with frequent rainfall. Called etiolation, grass blades and stems turned yellow and began to elongate during high temperature and humidity. In rare cases, the symptoms were severe resulting in loss of turfgrass stands. The results provide clues that bacteria may be responsible for damaging bentgrass greens. Yet, the over-use of some plant growth regulators may increase the occurrence of this problem.
Since 2010, scientists at North Carolina State University isolated 228 bacteria from 64 locations. Several bacteria included species from Acidovorax, Bacillus, Enterobacter, Microbacterium, Pantoea, Pseudomonas, Stenotrophomonas and Xanthomonas. Known plant pathogens Acidovorax avenae and Xanthomonas campestrins were present in less than 30% of the samples. Some isolates of Pantoea sp. caused chlorosis and dieback. Pantoea bacteria did not cause leaf and stem elongation when compared to A. avenae inoculations. Continued research will explore the diversity of bacteria living within turfgrasses.
Field observations of bacterial etiolation suggested biostimulant and plant growth regulator applications encouraged symptoms. The research showed biostimulants to have little effect. But, frequent applications of trinexapac-ethyl (PrimoMaxx at 0.125 fl oz. 1000 ft2 every 7 days) increased etiolation caused by A. avenae.
In 2013, an additional field study was initiated to evaluate the impact of plant growth regulators PrimoMaxx SC (trinexapac-ethyl), Trimmit SC (paclobutrazol), and Cutless 50W (flurprimidol) on bacterial etiolation caused by A. avenae. Results from the 2-year trial were similar to previous trials in that PrimoMaxx increased symptoms compared to the non-treated control; however, multiple rates of Trimmit and Cutless decreased etiolation symptoms compared to PrimoMaxx applied every 7 days (Figure 1). PrimoMaxx applications still resulted in the highest turf quality, as turf was not damaged as a result of A. avenae inoculations. High rates of Trimmit and Cutless did cause phytotoxicity during periods of low nighttime temperatures, but turf eventually recovered.
Based on this research, reducing the frequency of PrimoMaxx applications or altering plant growth regulator programs with Trimmit or Cutless can maintain quality playing conditions while limiting etiolation.
Source: Joseph A. Roberts