Research Report
Characterizing the Geographic Footprint of Ophiosphaerella Species Causing Spring Dead Spot of Bermudagrass in Virginia Virginia Tech Researchers: David McCall, Turfgrass Pathologist and Research Associate, Elizabeth Bush, Senior Research Associate, and Scott Johnson and Katie Dougherty, Undergraduate Students Research Sponsors: USDA-NIFA, Extension IPM Program
S
pring dead spot (SDS) is the most common and destructive disease of bermudagrass turf in marginal regions of adaptation, including throughout the Mid-Atlantic. In addition to being unsightly, the depressed voids left behind can potentially be an injury hazard on athletic playing surfaces. While documentation of the disease dates back over four decades, its epidemiology is still largely a mystery. Chemical and control strategies often produce inconsistent results. When various tactics are successful, it is typically a gradual improvement over several seasons. Our research in Virginia has shown that even with well-timed fungicide applications in the fall, a minimum of two years is needed for substantial suppression of the disease. The same mantra has proven true in other states, both with chemical and cultural strategies. Expected responses by managing with fertility have proven even slower. Research from Maryland in the late 1980s indicated that SDS may be effectively managed over time with the use of ammonium sulfate as a primary nitrogen source. This became the industry go-to for turf managers who chronically struggled with the disease. However, results have been highly
variable with stories of success, failure and everything in between. More recently, the pathology team at NC State determined that management with fertility was highly dependent on the causal agent species under artificially induced conditions. The researchers from NC State concluded that Ophiosphaerella herpotricha (Oh) is best managed with ammonium sulfate, whereas O. korrae (Ok) is unaffected. Conversely, calcium nitrate appears to be much more effective at suppressing Ok, with little to no effect on Oh. While this finding appears to be a breakthrough in our understanding of SDS epidemiology, field studies in Virginia under natural populations were highly inconsistent. One reason appears to be related to the speciation of the causal agent. Our current understanding of SDS is that the disease is caused by three species of Ophiosphaerella. Historically, species distribution is separated into geographies. O. narmari is known to incite disease in Australia and New Zealand, with a few isolated pockets in the U.S. Oh is typically considered the dominant species in the Midwest and more northern portions of the transition zone. Ok dominates in Southeastern states where SDS is a problem. To muddy waters even more, there have been confirmed
20 | Virginia Turfgrass Journal May/June 2015 www.vaturf.org
cases where multiple species are present in the same field. The geography of Virginia places our turf managers right in the battleground over which species to manage against.
Our research
As reported in the November/ December 2013 issue of the Virginia Turfgrass Journal, localized sampling confirmed that both Oh and Ok species are present in Virginia, but that one species tends to dominate a site-specific population. In order to make the greatest strides in disease suppression, geography-based control recommendations are needed to minimize the severity of SDS. Using a rapid diagnostic method, the Virginia Tech Turfgrass Pathology and Plant Disease Clinic labs have been working in collaboration to more clearly define the distribution of the two primary pathogens responsible for SDS in Virginia. Symptomatic plant tissue was collected from roughly 50 locations in Virginia and surrounding states. The presence or absence of each species was determined using published primer sets specific to internal transcribed spacer regions of each species using real-time polymerase chain reaction (qPCR). Each location