The Acidovorax/etiolation issues visited the Midwest during the past 2 weeks. There were multiple confirmed reports of etiolation on creeping bentgrass putting greens, but no confirmed reports of the decline phase. The latest peer-reviewed research clearly associates etiolation with trinexapac ethyl (TE), i.e., Primo. Symptoms appeared in plots treated weekly with about 0.125 fl oz/M, and at 14-day intervals with about 0.25 fl oz/M. No etiolation was present in research plots treated with root-absorbed GA inhibitors, flurprimdol (Cutless) or paclobutrazol (Trimmit). The prohexadione calcium GA inhibitor (Anuew) was not included in the test. Research was conducted in Acidovorax-inoculated field plots. Although the etiolation was present in the TE plots, once they were mowed, the TE plots resulted in the highest visual turf quality ratings!
We tend to ignore etiolated tillers anywhere other than greens and collars. Figure 1 shows etiolated creeping bentgrass on a practice range tee. I brought a sample to the lab and immediately observed bacterial streaming under the microscope. The image shows the most symptomatic area on the tee (30k sq ft). Etiolation has not progressed into a decline. Not one of the 11 other guys in my regular golf group commented on the odd-looking grass.
It is rumored that some superintendents are being encouraged to apply a hydrogen dioxide product (Zerotol) between sprays–or treating equipment with it after mowing symptomatic greens. The likelihood that such a surface disinfestant would reduce incidence or severity of the etiolation and/or the Acidovorax is beyond remote. Supers are being ill advised. It is disappointing because there is no evidence that the hydrogen dioxide will be effective. In a published study on the Poa annua bacterial wilt pathogen (Xanthomonas), plots treated with hydrogen dioxide were never any better than untreated check plots. There is evidence that hydrogen dioxide can aggravate a dollar spot outbreak by reducing natural competitors to the Sclerotinia homoeocarpa mycelium.
In 2012, etiolation progressed into decline during the 100 days of hell that persisted through September in the Midwest. To date in 2016, extraordinary heat and drought conditions have not occurred. Hopefully we can escape serious effects this year—and then learn more during the off-season about how and when infection actually occurs. That will be the first step in developing consistent and reliable control methods.