Research Report
Impact of Fraze Mowing on Spring Dead Spot Severity and Recovery Virginia Tech Researchers: Camden Shelton, Graduate Research Assistant; Jordan Booth, Graduate Research Assistant; and David McCall, Ph.D., Research Associate Research Cooperator: Rodney Hopkins, Innovative Turf Application and Consulting, and Lee Miller, Ph.D., University of Missouri
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ybrid bermudagrass (Cynodon dactylon) is one of the most desirable turfgrass species for sports fields and golf course playing surfaces in Virginia because of its aggressive growth habits, traffic tolerance, uniformity and color. Spring dead spot (SDS), caused by the fungal pathogens Ophiosphaerella korrae and O. herpotrica, is the most destructive disease of bermudagrass in Virginia and one of the biggest limiting factors to the success of hybrid bermudagrasses as playing surfaces. As the name implies, symptoms of SDS first appear in the spring, when bermudagrass resumes growth from its normal winter dormancy. As the turf breaks dormancy and begins to turn green, circular patches or rings of turf appear to remain dormant and eventually collapse to the ground and die. The disease is usually most severe after the turf is three to five years old as fungal populations and thatch accumulation increases. The pathogen survives in the thatch and infects the plants in the late summer and fall. Hybrid bermudagrasses that tend to produce excessive thatch are more prone to the disease. A unique characteristic of SDS is that the pathogens do not kill bermudagrass directly. These fungi attack the roots, rhizomes and stolons of bermudagrass in the fall and winter and increase the bermudagrass’ susceptibility to cold and freezing injury. Fall fungicide applications, properly timed cultural practices and coldtolerant bermudagrass varieties form an integrated approach to managing the disease.
Cultural practices are a vital part of an integrated pest management program. Cultural practices include but are not limited to proper mowing and watering practices, core aeration, sand topdressing and vertical mowing. Most of these practices are designed to manage thatch in the profile. The inherent problem with these practices is the disruption to the playing surface, and a common result is an insufficient thatch-management program that never really keeps up with the excessive thatch produced by hybrid bermudagrasses and other varieties. A new technique being employed is a process known as “fraze mowing” or “fraise mowing.” Fraze mowing and the equipment used to fraze mow was developed by Ko Rodenburg of the Netherlands for the renovation of cool-season turfgrass fields. Rodenburg developed a rotary tiller-type machine (KoRo) that takes off the top layer of the turf, leaving just the roots, rhizomes and some crowns, depending on the height of cut. The debris, which can be utilized as compost or sprigs in bermudagrass applications, then comes out on a conveyer belt located on the side of the machine. Fraze mowing helps promote new growth and also eliminate thatch and organic buildup on the surface. It also helps decrease weed seed and some cases of black layer. This process is very aggressive (not applicable in all situations), and it takes some time to recover. The noted benefits of thatch removal after fraze mowing led to the question amongst turf researchers: Can fraze mowing reduce SDS inci-
12 | Virginia Turfgrass Journal May/June 2016 www.vaturf.org
dence and/or severity and aid in the recovery in hybrid bermudagrass?
Our research
A split-plot research trial was designed to compare SDS occurrence, severity and recovery in hybrid bermudagrass plots under different fraze mowing depths and nitrogen sources. The trial was established on a ‘Patriot’ hybrid bermudagrass soccer field at the Striker Park, West Creek Complex in Richmond, VA. Fraze mowing occurred on May 29, 2015, and again on June 24, 2016, using a KoRo Imants Field Top Maker (Macclesfield, Cheshire, United Kingdom). Fraze-mow treatments consisted of 0, 4 and 8 mm depths. Plots received weekly applications of 0.5 pounds of nitrogen for six weeks following fraze mowing, in the form of ammonium sulfate (21-0-0) or urea (46-0-0). The plots were rated weekly for bermudagrass recovery, SDS recovery and overall turf quality. Spring dead spot severity, incidence and percent disease were rated in June 2016 after overseeded ryegrass was transitioned. Plots are receiving weekly fertility again in 2016 following the June 24 fraze mow, and they are being rated for recovery. Disease ratings will be collected in late spring of 2017.
Our results to date
After one season, fraze mowing at a depth of 8 mm reduced the incidence (number of SDS patches), severity of patch destruction and overall diseased area compared to the nonfraze-mowed control, when both were