Turf Talk
Spring Dead Spot: What Can You do to Manage This Disease?
By Wendell J. Hutchens, Ph.D. student under supervision of David McCall, Ph.D., Virginia Tech
Introduction The spring of the year is unpredictable for bermudagrass managers in the transition zone. Winterkill and spring dead spot (SDS) can devastate turfgrass stands. Affected bermudagrass exhibits necrotic circular patches at greenup —damage caused by SDS is both aesthetically and economically detrimental, and also provides an uneven playing surface that may increase the likelihood of sports-related injuries (Figure 1). Managing SDS is a year-round task—not just in the fall as previously thought. Preventative fungicide applications employed in the fall are typically the most effective for reducing SDS. However, cultural practices performed throughout the year can impact disease incidence, severity, and recovery. Turfgrass managers should maintain proper soil fertility and pH, apply effective fungicides, and implement other cultural practices to mitigate disease development. Figure 1: Outbreak of spring dead spot on a bermudagrass fairway. (Photo by David McCall)
Soil fertility and pH A fundamental concept of plant pathology is that healthy plants are more likely to withstand pathogen infection, and this holds true with SDS of bermudagrass. Proper soil fertility and pH is vital for turfgrass health. Maintaining proper soil fertility and pH improves the edaphic environment for turfgrass, allowing the plant to outcompete the pathogen. Certain reports suggest that soil pH for bermudagrass should be maintained close to 5-5.3 to mitigate SDS (Dernoeden et al., 1991; Vincelli et al., 1995; Vincelli et al., 1998). Moreover, a pH of 6 has been shown to increase Ophiosphaerella spp. growth in vitro while a pH of 5 or 7 can reduce fungal growth in vitro (Cottrill et al., 2016). The impact of late-season nitrogen applications has proven inconsistent. One study showed that late-season nitrogen applications increased SDS development (McCarty et al., 1992), yet results have been difficult to duplicate and other studies have suggested otherwise. Late fall applications of potassium sulfate are not recommended as SDS severity can increase the following spring (McCarty et al., 1992). In contrast, monthly applications of ammonium sulfate from May through September can reduce SDS incidence and severity the following spring (Dernoeden et al., 1991). Also, the application of sulfur in conjunction with fungicides over multiple years has the potential to reduce spring dead spot; however, three monthly sulfur applications (87.43 lbs acre-1) may cause phytotoxic effects and slowdown spring greenup (Cottrill et al., 2016). Recent research has also shown that Ophiosphaerella korrae can be suppressed by calcium nitrate applications while Ophiosphaerella herpotrica can be suppressed by ammonium sulfate (Butler, 2017). In contrast, a recent study from the Midwest showed that nitrogen source alone had no effect on SDS control (Cottrill et al., 2016). Although the results have been variable, application of proper fertility and nitrogen source is a potential method for reducing the disease. That being said, the driving factors of SDS epidemics are still not well understood.
SDS fungicide applications Fungicide applications are the most effective preventative control measure for SDS, particularly with several new chemistries available today. Various researchers throughout the United States have shown that penthiopyrad (Velista), isofetamid (Kabuto), and pyraclostrobin + fluxapyroxad (Lexicon) provide good SDS suppression (Booth et al., 2018; Earlywine and Miller, 2019; Galle et al., 2019; Freund et al., 2019; Roberson et al., 2017). While suppression is less consistent, many turfgrass professionals apply tebuconazole as a more affordable option. The introduction of these products and other novel chemistries provides new hope for increased SDS control. 20 | Virginia Turfgrass Journal May/June 2019 www.vaturf.org
