Off the Record: NC State researchers lead charge in spring dead spot prevention studies

At North Carolina State University, Lee Butler, Jill Ploetz and Jim Kerns, Ph.D., continue to provide a wide range of fungicide studies to prevent turfgrass diseases. They routinely conduct spring dead spot (SDS) disease prevention on bermudagrass fairways at their Turfgrass Field Lab in Raleigh, N.C.

Mike Kenna, Ph. D.

SDS symptoms appear in circular patches from six inches to several feet in diameter. The infected areas remain dormant as the turf greens up in the spring, and the patches eventually die. SDS patches recur in the same spot each year and increase in size each season.

Cultural practices to help prevent the disease include avoiding late fall nitrogen applications, reducing thatch and aerifying to reduce soil compaction. Fall fungicide applications when soil temperatures are between 60 and 80 degrees F can help prevent SDS. Mapping the affected areas in the spring can save money by only applying expensive fungicides in diseased areas.

The research team evaluated Posterity (pydiflumetofen) for preventing SDS in an 8-year-old Champion bermudagrass putting green. The rootzone followed USGA recommendations for putting greens. The team mowed plots six times weekly at 0.15 inches with clippings collected and applied treatments in water equivalent to 2 gallons per 1000 ft2 with a CO2-powered sprayer with a single TeeJet AI9508E nozzle at 50 psi.

Treatments included Posterity 1.67 SC at 0.16, 0.24 and 0.32 fl. oz. per 1000 ft2, Velista 0.5WDG at 0.5 oz. per 1000 ft2, and a nontreated control. They applied the treatments on Oct. 17 and Nov. 22, 2019, and immediately watered in with 0.2 inches post-application irrigation. They evaluated the severity of SDS on March 27, April 28 and May 26, 2020, to visually estimate the percentage of diseased areas.

SDS severity peaked at 37.4 percent on March 27 in the nontreated control plots and declined to 26.1 percent in the nontreated control through May 26. All treatments suppressed SDS compared to the nontreated control at each rating date. On April 28 and May 26, plots treated with Velista and Posterity at 0.24 fl. oz. and 0.32 fl. oz. provided better suppression of SDS.

In a second SDS trial on the same green, researchers tested Posterity Forte 2.5SC (i.e., a combination of pydiflumetofen, azoxystrobin and propiconazole) and Posterity 1.67SC alone, with Headway 1.39ME or Appear II 4.1SC, and with both Headway and Appear II. They applied treatments on Oct. 17 and reapplied on Nov. 9 or 21, 2019.

Researchers assessed the severity of the SDS on March 27, April 28 and May 26, 2020, as a visual estimation of the percentage of the diseased area within the plot. In the nontreated control plots, SDS severity peaked at 25.9 percent on March 27, and by May 26, only dropped to 21 percent. All treatments successfully suppressed SDS compared to the nontreated control on each rating date (March range = 2.3 to 6.4 percent, April range = 0.2 to 1.2 percent and May range = 0.3 to 2.0 percent).

These SDS fungicide trials and the studies at Clemson University demonstrate the effectiveness of commercial products for fairways and putting greens. However, the cost of blanket treatments of all fairways is often prohibitive. Turfgrass pathologists recommend mapping where the disease occurs in the spring.

I would direct your attention to this month’s research article from Virginia Tech University that is taking precision fungicide applications to the next level. Progress with identifying effective fungicides, mapping with drones and targeted precision sprayer applications will dramatically improve the prevention of SDS. These advancements will save money and provide more sustainable SDS prevention.