"Managing Spring Dead Spot in Hybrid Bermudagrass"

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Turfgrass Disease Information Note 4 (TURF-004)

E.L. Butler, Turfgrass Pathologist

L.P. Tredway, Extension Plant Pathologist


Pathogen: Ophiosphaerella korrae and O. herpotricha

Turfgrass Hosts: Bermudagrass

Season: Infection occurs in the fall, symptoms apparent following spring


[General Information] [Cultural Management]
[Chemical Control] [Summary]
[Back to Turfgrass Disease Information Notes]


General Information

Spring dead spot is, without question, the most severe disease of bermudagrass in North Carolina. The disease appears in circular patches or rings that remain dormant as the bermudagrass comes out of winter dormancy (Figure 1). The turf in these patches eventually collapses to the ground, leaving sunken areas in the turf that severely detract from its uniformity and playability (Figure 2). Injury from spring dead spot (SDS) often lingers well into the summer, and in some cases, the turf may not fully recover before fall dormancy (Figure 3).

 
Figure 1. Spring dead spot of bermudagrass
on an athletic field.


Figure 2. Sunken patches of spring dead spot.
 
Many golf course superintendents and athletic field managers have tried to manage SDS, only to obtain mediocre results. This has led many to conclude that the disease cannot be controlled. It is possible to manage SDS, but effective management requires an integrated approach, as well as a significant amount of patience and persistence.
 

Spring dead spot is unlike any other turfgrass disease, so therefore it must be managed differently. Unlike most turfgrass diseases, which affect the foliage, SDS does its damage below-ground. To demonstrate this, take a cup cutter plug from the edge of a SDS patch and break it apart. Few rhizomes and roots are present in the soil profile, and those that are present are black and rotten (Figure 4). You will also notice that the below-ground structure of the turf is very weak (Figure 5).
 
Figure 3. Severely damaged area of bermudagrass in which symptoms lasted well into summer.

Figure 4. Necrosis of stolon and roots
by spring dead spot.
 
To manage spring dead spot, your goal is to re-establish the below-ground structure of the bermudagrass turf. This is not something that can be accomplished in a single growing season, so SDS management is a multi-year venture. You will probably not achieve 100% control in the first year, but you will notice a gradual reduction in the disease over a period of years.

Another unique characteristic of SDS is that the pathogens, Ophiosphaerella korrae and O. herpotricha, do not kill bermudagrass directly. These fungi attack the roots, rhizomes, and stolons of bermudagrass in the fall and winter and increase the bermudagrass' susceptibility to cold and freezing injury. Management practices that improve the cold-hardiness of bermudagrass are therefore very effective for SDS management. In addition, bermudagrass varieties with improved cold tolerance are more resistant to SDS. Guymon, Midlawn, Midfield, Midiron, Yukon, Mirage, and Sundevil have been shown to have improved resistance to SDS, whereas Arizona Common, Cheyenne, Jackpot, NuMex Sahara, Oasis, Poco Verde, Primavera, Princess, Sonesta, Shanghai, Tifton 10, Tifway, Tifgreen, Tropica, Vamont, and Sunturf are all susceptible to SDS.
 
Figure 5. Poor root structure due to infection by spring dead spot, where left side of plug is diseased and right side is healthy.



Cultural Management of Spring Dead Spot

Cultural management practices have a tremendous impact on the winter hardiness of bermudagrass; consequently they also have a major effect on SDS development. A sound cultural program is critical to the success of any spring dead spot management program.

Any soil condition that reduces bermudagrass root growth will increase the severity of SDS. Soil compaction, poor soil drainage, and excessive thatch accumulations are the most common culprits. Many golf courses and athletic fields have areas that are devastated by SDS annually and one or more of these problems are almost always involved. The first step toward spring dead spot management is to evaluate the health of the soil and to alleviate any problems that exist. Regular aerification of high-traffic areas, at least 3 times annually, is needed to alleviate soil compaction. This will reduce spring dead spot problems and improve the overall quality of the turf throughout the season. In sites that are poorly drained, installation of subsurface drainage will help to reduce the disease. Excessive thatch is a common problem in higher heights of cut and areas that receive little traffic. Vertical mowing or aerification should be conducted as needed to maintain thatch accumulations below 1".

Nutrition and soil chemical properties are also important for SDS management. High nitrogen levels reduce the winter hardiness of bermudagrass and enhance the development of SDS. In general, no more than ½ lb of nitrogen per 1000 ft2 should be applied to bermudagrass after mid-September in North Carolina. When SDS damage does occur, the tendency is to increase nitrogen levels throughout the summer to speed re-growth into affected patches. If this nitrogen lingers into the fall, this will make the disease worse in the following year. Recovery from SDS should be encouraged by light, frequent irrigation and regular spiking or aerification, not by increased nitrogen levels.

Potassium applications in the fall have been shown to reduce SDS damage, again by increasing bermudagrass winter hardiness. Two fall applications of potassium chloride or potassium sulfate, totaling 1 lb K2O per 1000 ft2, on 3 to 4 week intervals is recommended. The timing of these applications is not critical, but September or October is probably best, so that the bermudagrass may absorb a significant portion of this potassium before it goes dormant.

Spring dead spot is most severe when soil pH is high, so the disease can be suppressed by maintaining soil pH between 5.5 and 6.0. Since bermudagrass is very tolerant of low pH, there is little risk of negative side effects at these pH levels. Elemental sulfur can be used to reduce soil pH, but this material must be used with extreme caution because it can directly injure the turf and can also drive pH levels too low. For this reason, elemental sulfur should only be used when soil pH is 7 or higher. Sulfur applications to fairways, roughs, athletic fields, and landscapes should not exceed 5 lbs/1000 ft2. Because sulfur is only activated when soil temperatures are above 50 ºF, applications should be made in the spring or fall when soil temperatures are above this threshold. Wait at least 6-8 weeks, then submit a soil sample for pH analysis, before making repeat applications of elemental sulfur.

Ammonium nitrogen sources, such as ammonium sulfate, are another effective means of reducing soil pH. These materials are safe, reduce the pH slowly, and can be applied as part of a regular maintenance program. When adjusting pH, have soil tests done on a regular basis to monitor the pH and ensure that nutrient levels stay in balance.



Chemical Control of Spring Dead Spot

Many turf managers have attempted to control SDS with preventative fungicide applications in the fall, only to see the disease recur in the following spring. This has caused most to abandon fungicide use in frustration. In fact, several extension services in the United States do not recommend fungicide applications for SDS control due to unreliable results.

On the other hand, several bermudagrass growers in North Carolina report excellent control of SDS with fungicides. What is their secret? They have been applying preventative fungicides on an annual basis for several years. Remember - SDS control is a multi-year venture. You will not achieve 100% control in the first year of a fungicide program, but the level of disease control will gradually increase over a period of years. If used in combination with proper cultural practices, one may eventually achieve complete control of the disease.

In order to maximize fungicide efficacy for SDS control, one must consider three important factors: fungicide selection, application timing, and application method. All three components are critical to ensure the success of a preventative control program.

In field studies at NC State, we have evaluated fenarimol (Rubigan), propiconazole (Banner Maxx, Propiconazole Pro), myclobutanil (Eagle), azoxystrobin (Heritage), and thiophanate-methyl (Clearys 3336). We have consistently found fenarimol to provide the best control of SDS, with propiconazole providing a moderate level of control (Figure 6). However, we have observed some negative side-effects resulting from fall applications of propiconazole, including increased susceptibility to frost and delayed spring green-up. For this reason, we are not recommending propiconazole for spring dead spot control until we can develop a better understanding of these negative side-effects.
 

Figure 6. Control of spring dead spot with fungicides applied on Sep 30 and Oct 31 2003.
Values taken from disease incidence ratings on May 13 2004.

The number of fenarimol applications is not as critical as the timing of applications. Our research has demonstrated that fall applications when soil temperatures are between 60ºF and 80ºF are most effective (Figure 7). The growth of bermudagrass roots is severely diminished when soil temperatures are below 60ºF, and their capacity absorb systemic fungicides may also be reduced. Where SDS pressure is low to moderate, one application of Rubigan 1AS (6 fl oz/1000 ft2) or an equivalent product is recommended when soil temperatures are between 60ºF and 80ºF. When SDS pressure is moderate to high, growers may choose to make two applications of Rubigan 1AS (4 to 6 fl oz/1000 ft2) on 4-6 week intervals when soil temperatures are in this critical range.
 

Figure 7. Control of spring dead spot with Rubigan 1AS with varying rate and initial date application
along with soil temperatures at time of application. Split applications were applied 14 days apart.

Equally important as fungicide selection and timing is the application method. Applications in higher volumes of water (>5.0 gal/1000 ft2) or applications in 2.5 gal/1000 ft2 that are immediately watered-in with 0.25" irrigation, tend to be more effective than applications applied in traditional carrier volumes of 2 gal/ 1000 ft2.



Summary

Spring dead spot can be managed with a multi-pronged approach, implemented over a period of several years. Use of resistant cultivars, improving soil conditions, proper nitrogen fertilization, fall potassium applications, and reduction of soil pH are the most effective cultural practices. Preventative fungicide applications are an option in high value areas or where cultural practices alone do not provide adequate control. Of the fungicides that are labeled for spring dead spot, fenarimol (Rubigan) is most effective and has not induced negative side-effects in our research trials. The precise timing of fungicide applications does not appear to be critical, as long as they are made in the fall before soil temperatures dip below 60°F. For best results, applications should be made in at least 5 gallons H20/1000 ft2 or watered-in with 0.25" of irrigation immediately after application in 2 gallons H20/1000 ft2.

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Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of registration and use patterns are subject to change by actions of state and federal regulatory agencies.

Published by the North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Last update to information: April 2005
Last checked by author: April 2005