The common disease name of “spring dead spot” is always one that causes a sense of urgent concern and worry. As bermudagrass emerges from winter dormancy and starts to green up, the visual appearance of circular patches of dead turf is an unwelcome surprise.
Visual symptoms of spring dead spot were first reported in 1936 in Oklahoma, where dead, circular patches were observed in bermudagrass sites following winter dormancy as the turf was progressing toward spring green-up. By the 1950s, the disease was called “spring dead spot,” with reports in many transition zone and southern locations in the U.S. and Australia. By the 1980s, researchers were beginning to use molecular biology to determine the pathogen responsible for this disease. Today, spring dead spot is caused by Ophiosphaerella herpotricha and Ophiosphaerella korrae in the U.S., and Ophiosphaerella narmari in Australia and New Zealand, with some reported cases in the U.S. These pathogens are ectotrophic root-infecting fungi that colonize roots, rhizomes and stolons.
When applying a fungicide for turf disease control, the fungicide’s active ingredient is most effective when the pathogen is active and viable, because the pathogen’s mycelia network is more likely to absorb the fungicide. Researchers at Virginia Tech (Blacksburg) wanted to determine the best time of year to apply fungicides to target the pathogen and therefore control spring dead spot. The fungicide application timings were based on time of year and soil temperature.
A two-year field study was conducted on fairway-height hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) at three locations in Virginia: Tifway mowed at 0.63 inch (1.6 centimeters), Northbridge at 1.0 inch (2.5 centimeters) and Patriot at 0.59 inch (1.5 centimeters). The sites had a history of spring dead spot caused by a mixed Ophiosphaerella sp. population.
The fungicides isofetamid and tebuconazole were applied at various timings based on a five-day average soil temperature at 0-4-inch (0-10-centimeter) depth: during the spring at 60 F (15.6 C), 65 F (18.3 C), 70 F (21.1 C), 75 F (23.9 C); in the summer at 80 F (26.7 C); in the autumn at 75 F (23.9 C), 70 F (21.1 C), 65 F (18.3 C), 55 F (12.8 C), 45 F (7.2 C); in early winter at 44 F (4.4 C) and late winter at 44 F (4.4 C). The fungicides were applied according to the rate listed on their product label. The fungicides were applied in 2-gallon water-carrier per 1,000 square feet (814 liters per hectare) followed by irrigation, except for the applications in the winter since the irrigation system was shut down at that time of year. All plots were evaluated for spring dead spot occurrence and severity from initial green-up in the spring into the summer.
At all three field study locations, a reduction in spring dead spot severity and therefore better disease control was associated with autumn fungicide applications, with isofetamid more effective compared to tebuconazole. Better fungicide efficacy from autumn applications may have been a reflection of favorable temperatures for the growth and activity of the pathogen. Additional laboratory studies on O. herpotricha and O. korrae isolates from those field trial sites revealed their optimum growth between 75-77 F (24-25 C), although both species were active at 52 F (11 C).
This research provided information on proper fungicide application timing for the management of spring dead spot. The data analysis revealed fungicide applications in the autumn when soil temperatures are near 55 F (12.8 C) provided the best opportunity to control spring dead spot in bermudagrass. Thus, applying a fungicide at the proper soil temperature and proper time of year are both necessary factors when targeting spring dead spot. Based on this research, the recommendation is to apply a highly efficacious fungicide one to two times during the autumn months when a five-day average soil temperature at the 0-4 inch depth ranges from 55-64 F (13-18 C). Also, within the parameters of this research, isofetamid suppressed spring dead spot more effectively than tebuconazole. Since tebuconazole has a high affinity to bind to organic matter, it is less likely to reach the pathogen located in the soil as compared to isofetamid. Therefore, while timing is everything, delivery is important, too.
Source: Hutchens, W.J., J.C. Booth, J.M. Goatley, T.L. Roberson and D.S. McCall. 2025. Optimizing fungicide application timing for spring dead spot based on soil temperature and season. Crop Science 65:e21411.
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 25-year member of GCSAA.