Posted by Brent Wilson on 8/10/2016 to Lawn Care
Bermudagrass is susceptible to several types of disease however, without question, spring dead spot is probably the most common and serious.
Though the infection occurs in fall, the symptoms of spring dead spot become apparent in spring. The disease appears in circular patches or rings that remain dormant as the rest of the lawn comes out of winter dormancy in spring. (Dead or brown patches that occur and appear in summer are not spring dead spot.) The grass in patches caused by spring dead spot usually dies out completely, leaving sunken, bare areas in the turf. Though the bare patches usually fill back by runners from surrounding turf, injury from spring dead spot often lingers well into the summer and sometimes doesn't fully recover before dormancy in late fall or early winter.
To get control of this spring dead spot requires an integrated approach and persistence. Unlike most turf diseases, which effect the foliage above the ground, spring dead spot is fungi that effects the roots below the ground. These fungi attack the roots, rhizomes, and stolons of bermudagrass in the fall and winter and increase the grasses susceptibility to cold and freezing injury. If you dig up a plug of dirt from an infected area you'll see that the roots and rhizomes are mostly rotten.
In controlling spring dead spot, your goal will be to re-establish the root system of the grass. Doing so takes time; usually two or more seasons. 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.
How to Control Spring Dead Spot
There are basically two methods used for controlling spring dead spot; cultural and chemical.
Cultural control are practices that improve the cold-hardiness of bermudagrass. These practices should be your first priority. Basically, if you can increase the cold hardiness of bermudagrass doing so will have a major effect on the spring dead spot.
Any soil condition that reduces bermudagrass root growth will increase the severity of spring dead spot. Compacted soil, poor soil drainage, and excessive thatch accumulations are the most common causes. So, the first step toward spring dead spot management is to evaluate the health of the soil and to alleviate any problems that exist.
If the soil is compacted, regular aerification (especially of high traffic areas) is needed one to three times yearly. This will reduce spring dead spot problems and improve the overall quality of the turf throughout the season.
In low lying areas that are poorly drained steps will need to be taken to improve drainage. Installation of subsurface drainage or regrading or filling low areas with topsoil will help to improve drainage and reduce the disease.
If you cut your bermudagrass lawn high (3 inches or more) thatch can become a problem. Thatch is a loose, intermingled organic layer of dead and living shoots, stems, and roots that develops between the zone of green vegetation and the soil surface. Dethatching or aerification should be conducted as needed to maintain thatch accumulations below 1 inch.
Nutrition and soil chemical properties are also important for spring dead spot management. High nitrogen levels in late summer or early fall can reduce the winter hardiness of bermudagrass and enhance the development of disease. Cease fertilization with "high-nitrogen" fertilizers at least two months prior to the average first frost date in your area. Nitrogen (N) is the first number in the three numbers you'll see on a bag of any type of fertilizer. A good rule of thumb is to not use high-nitrogen fertilizer after mid-August. Fall feeding should be done using a fertilizer that contains no more than 5% nitrogen. When spring dead spot 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 spring dead spot should be encouraged by light, frequent irrigation and regular spiking or aerification, not by increased nitrogen levels.
Application of potassium(K) in the fall have been shown to reduce spring deadspot damage, again by increasing bermudagrass winter hardiness. Most "Fall Feed" lawn fertilizers are high in potassium (the third and last number on the bag of fertilizer). The timing of fall feeding with a fertilizer low in nitrogen and high in potassium 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 (alkaline), so the disease can be suppressed by maintaining a more acid soil pH between 5.5 and 6.0. Since bermudagrass is very tolerant of low pH, there is little risk of negative side effects. Because sulfur is only activated when soil temperatures are above 50ºF, 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 to your local Extension service for pH analysis, before making repeat applications of elemental sulfur. If you don't have access to an Extension service or want to test your soil yourself, most nursery and garden centers carry soil testing kits .
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
Spring dead spot can also be controlled with fungicide applications, though this alone might not get total, long term control of the disease. Fungicides are usually most effective when combined with the cultural practices mentioned above.
When using a fungicide, keep in mind that you will most likely not achieve 100% control in the first year of treatment. Success comes from applying preventative fungicides on an annual basis for several 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 spring dead spot control, one must consider three important factors: fungicide selection, application timing, and application method. All three components are critical to ensure the success.
In field studies at NC State, they evaluated fenarimol (Rubigan), propiconazole (Banner Maxx, Propiconazole Pro), myclobutanil (Eagle), azoxystrobin (Heritage), and thiophanate-methyl (Clearys 3336). They have consistently found fenarimol to provide the best control of spring dead spot. That being said, I and many of the customers at our nursery and garden center have used Bonide Infuse Systemic Disease Control (Thiophanate-methyl - 2.08%) to successfully control spring dead spot and many other turf diseases.
The number of chemical applications is not as critical as the timing of applications. Fall application, when the infection occurs and soil temperatures are between 60ºF and 80ºF, are most effective. The growth of bermudagrass roots is diminished when soil temperatures are below 60ºF, and their capacity absorb systemic fungicides is also reduced. August through mid-September is a good time for chemical applications.
Whenever using a chemical always be careful to follow application instructions on the product label.
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