The two containers to the left feature greenhouse-grown Poa annua plants inoculated with bacterial wilt of annual bluegrass. The pair of containers on the right are uninoculated control plants for comparison.

Within the past decade, bacterial wilt of annual bluegrass has become a pernicious problem in the Northeast. While it is not observed as frequently as anthracnose or dollar spot, the disease can usually be found at low levels on most golf courses with a significant level of annual bluegrass infestation.

The University of Rhode Island Turfgrass Disease Diagnostic Clinic has isolated the pathogen from golf courses in Connecticut, Massachusetts, Montana, New Hampshire, New York, Pennsylvania, Rhode Island and Canada. When the disease does become aggressive, it is extremely difficult to manage. Under optimal conditions, the disease will move through a stand of annual bluegrass, killing existing plants and infecting newly emerged seedlings throughout the course of the growing season.

Table 1: Host range of the M-1 isolate of Xanthomonas translucens pv. poae, isolated from Torrington Country Club in Torrington, Conn., 2001.

Bacterial wilt of annual bluegrass was originally identified in the United States in 1985 in the lab of Dr. Joseph Vargas (Robertset al.1995). At the time, it was considered a strain ofXanthomonas campestris.The same lab also identifiedXanthomonas campestrispv.graminisaffecting only the creeping bentgrass cv. Toronto in the early 1980s.

In 1995 a major revision of the genusXanthomonaswas published and reclassified those Xanthomonads that attack grasses asXanthomonas translucens,a group of organisms that had been most previously revised under that name in the 1940s (Hagborg 1942).

To the left, growth of chamber-grown Poa annua plants inoculated with bacterial wilt of annual bluegrass. In the container to the right are uninoculated control plants for comparison.

The causal agent of bacterial wilt of annual bluegrass isXanthomonas translucenspv.poae(Mitkowskiet al.,2005). Researchers in Japan have been studying the pathogen since the early 1990s and have made significant progress in understanding its biology and pathogenicity. As the name implies, its host range is restricted to the genusPoa.It will not attack any other grass genus and only goes to a fewPoaspecies. While it is most aggressive on the annual form ofPoa annua,it can also killPoa trivialis.It has been observed multiplying in the leaf tips ofPoa compressaandPoa pratensisbut has not been observed to cause disease on either of these species.

Its specificity forPoa annualed some researchers to investigate its use as aPoa annuabiocontrol. Unfortunately the pathogen is extremely difficult to artificially inoculate, requiring extremely large numbers of bacteria to initiate a successful infection, thus limiting its potential as a biological control.