How bermudagrass recovers from spring dead spot

Ophiosphaerella spp. distribution in the Mid-Atlantic. Species were determined using real-time PCR, and regions are color-coded: Red=VA Mountains; Blue=VA Piedmont; Orange=VA Coastal Plain; Green=DE, MD, and NC. (Graphic courtesy of Wendell Hutchens)

Hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) is one of the most desirable turfgrasses for golf courses in the Transition Zone because of its aggressive growth habit, traffic tolerance, uniformity and color (5,7).

Spring dead spot (SDS), caused by Ophiosphaerella spp., is one of the most devastating diseases on all bermudagrass (Cynodon spp.) grown in areas where winter dormancy occurs. Spring dead spot has a wide distribution throughout the U.S., with 24 states reporting the disease (5, 6).

As the name implies, symptoms of SDS first appear in the spring when bermudagrass begins to green up. Circular patches or rings of turf remain dormant and eventually die. Spring dead spot does not directly kill bermudagrass, but the fungi can attack the roots, rhizomes and stolons in the fall, increasing susceptibility to cold and freezing injury during the winter (2, 7, 8, 9).

O. herpotricha and O. korrae are the two predominant species that cause SDS in the Mid-Atlantic region of the U.S. (5, 6). Ophiosphaerella spp. was found within the three geographic areas of Virginia and the surrounding states (Figure 1).

Locations west of Charlottesville (78.5 degrees W) had more O. herpotricha than locations east of that longitude, whereas areas east had more O. korrae (5). Moreover, O. herpotricha and O. korrae frequency of occurrence can also be influenced by cultivar (6). Due to the geographic variability of species, we recommend submitting SDS samples to a diagnostic clinic for accurate identification.

Spring dead spot is a challenge to manage in Virginia. Most research efforts for SDS recommend employing preventive practices such as fungicide applications and other cultural practices in the fall. We often overlook recovery strategies from damage in the spring and early summer.

Previous research at Virginia Tech University evaluated fraze mowing for recovery and long-term suppression of SDS (7). Fraze mowing removes most surface plant material and thatch, which provides a smoother playing surface.

Fraze mowing was conducted on May 29, 2015, at 0.16 and 0.32-inch depths. Granular broadcast applications of urea and ammonium sulfate (0.5 lbs. N per 1,000 ft²) followed trial initiation and every seven days afterward for six weeks. Visual and reflectance data show fraze mowing treatments yielded higher turf quality, and plots treated with ammonium sulfate recovered faster than plots treated with urea, regardless of depth (7).

Main effect of fertility on bermudagrass recovery area under the progress curve (AUPC). Means are compared within years, and colored bars represent different fertility practices. Bars within the same year with distinct letters are significantly different (P = 0.05). (Graphic: Golfdom Staff)

Cultivation practices

Our objective was to evaluate other cultivation practices for their impact on bermudagrass recovery from SDS. We conducted a field trial from May 30 to Aug. 12, 2019, and repeated from June 25 to Aug. 6, 2020, on NorthBridge bermudagrass in Blacksburg, Va. There were six treatments in the study:

• Non treated control
• Two applications of urea two weeks apart, totaling 2 lbs. N per 1,000 ft²
• Verticutting
• Solid-tine verification
• Verticutting plus two applications of urea two weeks apart, totaling 2 lbs. N per 1,000 ft², and
• Solid-tine aerification plus two applications of urea two weeks apart, totaling 2 lbs. N per 1,000 ft²

We evaluated plots for percent SDS throughout the study. Data were analyzed as percent SDS change relative to
an initial assessment to measure bermudagrass recovery from SDS. The data were then converted to area under the progress curve (AUPC) to encompass bermudagrass recovery over time.

The main effect of fertility increased bermudagrass recovery by 19 percent in 2019 and 33 percent in 2020 compared to the non-fertilized plots (Figure 2). However, the main effects of solid-tine aerification and verticutting inhibited bermudagrass recovery in 2020 by > 32 percent compared to non-cultivated plots (Figure 3). There was no effect of cultivation on bermudagrass recovery in 2019.

Main effect of cultivation on bermudagrass recovery area under the progress curve (AUPC). Means are compared within years, and colored bars represent different cultivation practices. Bars within the same year with distinct letters are significantly different (P = 0.05). *NS represents not significant. (Graphic: Golfdom Staff)

This field experiment suggests that urea applications in the late spring or early summer are sufficient for optimizing bermudagrass recovery from SDS damage. In contrast, cultivation practices such as verticutting and solid-tine aerification early in the growing season, particularly without fertility, can inhibit bermudagrass recovery from SDS damage. The result is surprising since general recommendations to improve SDS recovery include cultivation practices (4, 7).

Over the last 30 years, research results strongly recommend nitrogen applications in the spring to enhance SDS recovery (2, 3, 4) and agree with previous fraze mowing experiments (7). An older experiment in Maryland evaluated several different nitrogen sources in combination with potassium chloride (2, 3). All nitrogen treatments helped speed recovery from SDS in the first year.

Fertilizer with ammonia (NH4-N) reduced SDS occurrence in the second and third years of the trial. The soil pH data indicate that soil acidification by ammonia nitrogen helped reduce SDS severity over time.

Our recommendation is to fertilize with 2 lbs. N per 1,000 ft² in the spring if the bermudagrass suffers damage from SDS. We also recommend delaying traditional cultivation practices such as verticutting and aerification until the damaged areas have recovered. Future research will focus on other cultivation methods and the effect of various fertilizer types on bermudagrass recovery from SDS.

Research takeaways

• Ophiosphaerella herpotricha and O. korrae are the two predominant species that cause SDS in the Mid-Atlantic region of the U.S.
• Two spring applications of urea (a total of 2 lbs. N per 1,000 ft²) enhanced NorthBridge hybrid bermudagrass recovery from spring dead spot (SDS) in the first year.
• Solid-tine aerification and verticutting did not improve SDS recovery in the spring.

Wendell Hutchens is a Ph.D. graduate student at Virginia Tech University and can be reached at wendelljh@vt.edu. Mike Goatley, Ph.D., and David McCall, Ph.D., are faculty at Virginia Tech University.

The full peer-reviewed article of this work can be found in HortScience https://doi.org/10.21273/HORTSCI16235-21

References

1. Beck, L.L.; Cooper, T.; Hephner, A.J.; Straw, C.M.; Henery, G.M. 2013. Effect of pre-emergence herbicides on bermudagrass recovery from SDS. Golf Course Management. July. 81(7): p. 80-85. https://archive.lib.msu.edu/tic/gcman/article/2013jul80.pdf
2. Dernoeden, Peter H. 1991. Reducing Spring Dead Spot Severity. Golf Course Management. March. 59(3):68,70,72,74,80. https://archive.lib.msu.edu/tic/gcman/article/1991mar68.pdf
3. Dernoeden, P.H.; Crahay, J.N.; Davis, D.B. 1991. Spring Dead Spot and Bermudagrass Quality As Influenced by Nitrogen Source and Potassium. Crop Sci. 31:1674-1680.
4. Dowling, Elliott L. 2017. Spring Dead Spot. USGA Regional Update. May 5, 2017. 2pp. https://tic.msu.edu/tgif/urltab?RECNO=312972
5. Hutchens, W. J., Henderson, C. A., Bush, E., & McCall, D. S. 2019. Geographic Distribution of Spring Dead Spot Species in the Mid-Atlantic [Abstract]. ASA, CSSA and SSSA International Annual Meetings (2019), San Antonio, TX. https://scisoc.confex.com/scisoc/2019am/meetingapp.cgi/Paper/120049
6. Hutchens, W.J., Henderson, C.A., Bush, E.A., Kerns, J.P., and McCall, D.S. 2021b. Geographic Distribution of Ophiosphaerella Species in the Mid-Atlantic United States. Plant Health Prog. https://doi.org/10.1094/PHP-04-21-0076-S
7. Shelton, C. D.; McCall, D. S.; Miller, G. L. 2016. Impact of fraze mowing on bermudagrass recovery from spring dead spot. Proceedings of the First Annual Meeting of the Northeastern Plant, Pest, and Soils Conference. p. 44. http://www.newss.org/proceedings/Proceedings_NEPPSC16_Vol1.pdf#page=70
8. Tomaso-Peterson, Maria. 2009. The Efficacy of Spring Fungicide Applications Plus Organic Fertilizer for Controlling Spring Dead Spot of Bermudagrass. 2009 USGA Turfgrass and Environmental Research Summary. p. 11. http://archive.lib.msu.edu/tic/ressum/2009/11.pdf
9. Walker, N.R., Mitchell, T.K., Morton, A.N., and Marek, S.M. 2006. Influence of temperature and time of year on colonization of bermudagrass roots by Ophiosphaerella herpotricha. Plant Dis. 90:1326-1330. https://doi.org/10.1094/PD-90-1326