Summary

Spring dead spot continues to be a major problem for turfgrass managers in Georgia. It is one of the more difficult diseases to manage because acceptable control is usually not obtained in a single season.  Selecting proper nitrogen and potassium fertilization, thatch management and soil conditioning are important cultural practices that can help in reducing SDS. One or two fungicide applications in the fall are frequently necessary to achieve acceptable control.       

Introduction

Spring dead spot (SDS)is a persistent and destructive disease of bermudagrass (Cynodon sp.) in Georgia. The disease is problematic in golf course greenS and fairways, sports fields and residential settings with prevalence and severity being particularly high in the northern part of Georgia. However SDS can be observed throughout the state after harsh winters and in areas where bermudagrass has been exposed to freezing temperatures for extended periods of time. Ophiosphaerella korrae, O. narmari and O. herpotricha are the causal agents of SDS. O. korrae is the most common species in the southeastern United States, while O. herpotricha and O. narmari are more common in the western United States. Gaeumannomyces graminis var. graminis is also suspected to be associated with SDS in the southeastern United States. These fungi are active in the fall and spring when cool, moist conditions exist. They do not kill bermudagrass directly; instead they make turfgrass more susceptible to cold and freezing injury by feeding on roots, rhizomes, and stolons. The production of spores is thought to be rare for O. herpotricha but more common for O. korrae. Therefore, spread of these fungi primarily occurs through movement of infected plants or infested soil by equipment, people, animals, and running water. Infection of the turfgrass begins when soil temperatures are less than 70°F. Typically, in Georgia infection of susceptible grasses begins in late September/Early October and will continue as long as soil temperatures are above 50° F. These temperatures occur both in the fall and also in the spring allowing fungal growth and plant infection to resume in early spring coinciding with bermudagrass transitioning from winter dormancy

Fig.1. Spring Dead Spot Symptoms. Multiple circular patches of dead, bleached grass are evident in Spring. Grass at the center of patches is completely deteriorated. Sharp edges of dead and healthy grass are evident once turfgrass greens up in spring. Centers of patches are usually colonized by weeds. (Photos Alfredo Martinez)

Symptoms

As turfgrass “greens up”, well-defined circular patches of dead, bleached-out grass are noticeable in affected areas (Figure 1). Non-infected bermudagrass resumes growth, accentuating the infected areas. Roots, rhizomes and stolons are sparse and dark-colored (necrotic) (Figure 2). Leaves become bleached, gray and straw-colored. Recovery from the disease is slow. Since the turfgrass in affected patches is dead, the primary means of recovery occurs by spread of stolons into the patch. Because recovery is dependent on lateral infill of surrounding bermudagrass, symptoms can remain visible well into the growing season. If not managed properly, these patches may reappear in the same location the following spring along with weed species that may invade the voids (Figure 3). Patches can get larger year after year.

Fig.2. Dark-brown to black roots and rhizomes of SDS affected Bermudagrass (top). Compare with healthy rhizomes and roots (bottom). (Photo Alfredo Martinez)
Fig.3. Weed establishment filling voids caused by SDS patches. (Photo Alfredo Martinez)

Disease management

Diagnosis

While SDS symptoms are unique and conspicuous, initial identification can be difficult. Definitive identification often requires the intervention of expert diagnosticians. The University of Georgia County Extension Agents (https://extension.uga.edu/county-offices.html) in collaboration with the UGA CAES Plant Pathology Department Plant Disease Clinic (https://plantpath.caes.uga.edu/extension/plant-disease-clinics.html) offer support in the diagnosis. UGA extension personnel can work with you in the deployment of the latest SDS management strategies.

Cultivar selection and cultural practices

The primary cultivars grown and used in sport fields in Georgia are susceptible to SDS. In general, cultivars with more cold tolerance have less SDS than non-cold tolerant bermudagrasses. On sites where SDS has been a chronic problem, conversion to a tolerant cultivar is an option for disease management. Complete control of SDS in a single growing season is uncommon. It typically takes two to four years of proper cultural management and fungicide applications before acceptable control can be achieved. This has led to SDS becoming one of the more difficult diseases for growers to manage on an annual basis. Cultural practices that improve the cold-hardiness of bermudagrass can be particularly effective for managing SDS. Proper use of nitrogen fertilizers is important because high nitrogen levels can reduce the winter hardiness of bermudagrass. It is recommended that no more than  ½ lb of nitrogen per 1000 ft2 be applied after mid-September. Potassium applications in the fall (September or October) that total 1 lb K2O per 1000 ft2 can be helpful in improving the winter hardiness of bermudagrass and thus reduce SDS severity. Potassium applications should be applied based on results of soil tests. A neutral to slightly alkaline soil pH has been linked to increased severity of SDS. Maintain soil pH at 5.8 to 6.2. Use acid-forming fertilizers on sites with near neutral to alkaline pH. Apply iron, manganese, and other micronutrients based on results of soil tests. You can select a soil test at your local extension office that measures iron and manganese and adjust levels based on the results. Any soil condition that reduces bermudagrass root growth such as compaction, excessive thatch (> ½ in), and poor drainage can also increase the severity of SDS.  Core aeration and other practices that reduce soil compaction and encourage the production of new roots can be helpful in managing this disease. 

Chemical control

Timing, selection, and application of fungicides are important for preventative management of SDS. Research has shown that one application of fungicide in the fall when soil temperatures are between 60° and 75° F provides the best control of SDS.  When disease pressure is high, growers may want to make two applications. If a second application is necessary, it should be made 4 to 6 weeks after the first application when soil temperatures are between 60° and 75° F (visit http://www.georgiaweather.net/ for up-to-date meterological information at your, or near your location). For improved results, it is recommended that fungicide applications be applied at high spray volumes (> 5.0 gal/1000 ft2) and immediately watered-in. There have been mixed results from turfgrass managers around the state regarding chemical control of SDS. Those who have seen good results indicate they spray preventative fungicides that target SDS each year and have been doing so for several years. Therefore, it is important to keep in mind that controlling SDS takes time and usually cannot be obtained in a single season.  for a complete list of fungicides, formulations and specific information for SDS management consult the Georgia Pest Management Handbook (http://www.ent.uga.edu/pmh/) and the Turfgrass Pest Control Recommendations for Professionals (http://www.georgiaturf.com). Some fungicide options have specific site usage (i.e. are exclusively for golf course settings). If you are a homeowner and do-it-yourself consult the “home turf disease control” section in the Georgia Pest Management Handbook Home and Garden Edition. Always check fungicide labels for specific instructions, restrictions, special rates, recommendations, follow up applications and proper handling.

This article was updated and modified from:

Identification and Control of Spring Dead Spot in Georgia. Alfredo Martinez, J.B. Workman, F.C. Waltz. UGA CAES Extension Circular 1012. https://secure.caes.uga.edu/extension/publications/files/pdf/C%201012_4.PDF

Authors: Alfredo Martinez Espinoza1, Ruchika Kashyap2 and Garrett Hibbs3

1University of Georgia Plant Pathology Department-Griffin campus, 2University of Georgia Plant Pathology Department-Athens Campus and 3Agriculture and Natural Resources County Agent, Hall County

References

Butler, E.L. and Tredway, L.P.  2005.  Turfgrass – Managing Spring Dead Spot in Hybrid Bermudagrass.  Factsheet, NC State.

Couch, H.B.  2000.  The Turfgrass Disease Handbook.  Krieger Publishing Company, Malabar, Florida.

Hagan, A. 2000. Control of Spring Dead Spot and Bermudagrass Decline. Publication ANR 371. Alabama Cooperative Extension System.

Smiley, R.W., Dernoeden, P.H.  and Clarke, B.B.  2005.  Compendium of Turfgrass Diseases. Third edition.

Smith, D. L., and Walker, N.R. 2009. Spring Dead Spot of Bermudagrass. Oklahoma Cooperative Extension Fact Sheet EPP 7665.

Tredway, L. P. Tomaso-Peterson, M., Hunter P., and Walker, N. R. 2008.  Spring Dead Spot of Bermudagrass: A Challenge for Researchers and Turfgrass Managers. http://www.apsnet.org/publications/apsnetfeatures/Pages/Bermudagrass.aspx.