Bermudagrass Decline and Spring Dead Spot

Devastating diseases of warm season grass often take the form of root pathogens. Two of the more troublesome diseases for Golf Course Superintendents in the warm season grass markets are Bermudagrass Decline and Spring Dead Spot.

Bermudagrass Decline is a potentially devastating turf disease in the southern part of the United States from summer through fall when air temperatures consistently remain between 80-95 degrees F. Mechanical stresses caused by short mowing heights, verticutting for thatch management, and typical southern summer weather conditions of hot, moist air, and reduced sunlight (due to cloud cover) all create a favorable environment for disease development. Visual symptoms above ground may include leaf-yellowing originating from the base of the plant, a thinning turf stand, and reduced response to fertilizer and irrigation inputs. Closer inspection of the root systems reveal a thin and shallow root system consisting of short, brown or black roots with little evidence of healthy feeder roots or root hairs. These symptoms are probably caused by the pathogen Gaeumannomuces graminis var. graminis.

Research has shown that no fungicide treatment provides acceptable curative control for Bermudagrass Decline. Curative treatments can provide some recovery, but trying to manage a compromised plant in a southern summer is often very difficult. The best course of action is to identify the problem areas and start a preventative treatment program at spring dormancy break in the following year. Applications of root penetrating, systemic fungicides such as 3336, the DMI group (Rubigan, and Eagle), and the Strobilurin group (Heritage and Insignia), have historically shown the best preventative results. Begin your treatment rotation using Cleary’s 3336 at the spring dormancy break or when soil temperatures at a two-inch depth reach 60-65 degrees F. Continued use of 3336 in a rotation with the other systemic fungicide groups has been shown to provide acceptable preventative disease control. Apply 3336 at a rate of 6-8 fl oz per 1,000 in a 14-21 day rotational program. For best results, apply 3336 after mowing and water the treatment into the active root zone using 1-2 tenths of an inch of water. Avoid the use of Strobilurin products repeated under extreme heat conditions as phytotoxicity has been reported under some circumstances.

Spring Dead Spot is the second major disease of Bermudagrass that is associated with a root pathogen, but this disease exhibits different symptoms and requires different management practices. Commonly associated with Ophiosphaerella (Leptosphaeria) narmari and O. korrae, this fungus is most active during the fall and spring favoring cool, moist conditions for infection. The ability to infect roots at soil temperatures between 55 and 70 degrees F give this disease a devastating advantage over the Bermudagrass host, due to the slow root growth at these temperatures. By the time weather conditions favor the growth of the host, the root system has been severely compromised. Visual symptoms above ground are distinct circular patches of bleached dead grass that appear in the spring at dormancy break. Closer inspection of the root zone reveals that it is severely rotted, showing a dark brown-black color and no evidence of new root development. Recovery of the surrounding healthy Bermudagrass into the affected patches is generally slow due the presence of a persistent toxin produced by the fungus.

As in the case of Bermuda Decline, curative treatments can provide some recovery, but trying to manage a compromised root zone in a southern summer is often very difficult. Once again, preventative treatment in areas of previous disease expression is advised. Applications of root penetrating, systemic fungicides such as 3336 and the DMI group (Rubigan, and Eagle), and the Strobilurin group (Heritage and Insignia), have historically shown the best preventative results. However, since this disease has a fall infection period, usually during the onset of dormancy, the treatment period must be drastically different that the management of Bermuda Decline. Research has indicated that the use of 3336 as a tank mix or in rotation with a DMI type product, such as Rubigan has consistently provided the best results when used as a two-application fall program or a fall/spring split program. Apply 3336 at a rate of 4-6 oz in the fall, two applications at 21 day intervals starting 6-8 weeks before the expected onset of dormancy. Research has also shown that these applications are sensitive to water volumes and should be made with 4 gallons per 1,000 square feet (176 GPA), or applied and watered in with 1-2 tenths irrigation water to move the product into the active root zone. Apply 3336 at a rate of 4-6 oz in the fall/spring split program approximately 4 weeks before the onset of dormancy and again at the break of dormancy in the spring.

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