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Problem: Spring Dead Spot of Bermudagrass - Ophiosphaerella herpotricha
Host Plants: Bermudagrass
Description: Spring dead spot is the most common and destructive disease of bermudagrass in Kansas. Spring dead spot does not occur on cool-season turfgrasses such as tall fescue and Kentucky bluegrass. However, a patch disease of zoysiagrass, tentatively called zoysia patch, has many similarities to spring dead spot.
Spring dead spot may occur on bermudagrass lawns of all ages, although it typically appears 3-4 years after the turf has been established. The disease results in the formation of circular or arc-shaped patches of dead turf in early spring as bermudagrass breaks winter dormancy. The dead patches, which are slightly depressed and straw-colored, may range in size from several inches to several feet in diameter and normally are randomly distributed throughout the lawn. Roots and stolons of affected plants are often dark brown to black and are severely rotted. It may be necessary to dig up a piece of sod near the margin of the dead area and wash it in water to observe this symptom. Bermudagrass slowly recolonizes spring dead spot areas, and by late summer there may be little or no evidence of the disease. Unfortunately, enlarged dead patches reappear the following spring in the same locations. Over a number of years, the patches can become quite large, coalesce, and develop arc-like patterns in the lawn. After 7 to 10 years, disease severity may begin to decrease to the extent that spring dead spot no longer occurs in the lawn.
Ophiosphaerella herpotricha is a soil borne fungus that colonizes the roots, stolons, and crowns of bermudagrass plants in late summer or fall. Roots infected with the fungus turn dark brown to black as a result of the extensive fungal growth in and on the roots. Although most fungal colonization occurs in autumn, foliar symptoms do not develop until late spring. During the winter dormancy months, infected roots or crowns are either killed directly by the fungus or are predisposed to desiccation or cold temperature injury. Root colonization by the pathogen decreases the cold hardiness of the bermudagrass. The disease tends to be more severe on high maintenance bermudagrass lawns. Excessive nitrogen fertilization during the summer months enhances symptom development the following spring.
Recommendations: Several cultural methods may limit the severity of spring dead spot. The basic philosophy is to maintain a vigorous but not excessively managed turf. Lawns should be dethatched at regular intervals (yearly) when the bermudagrass is actively growing to promote good rooting. Avoid excessive nitrogen fertilization. Application of more than 4 lb active nitrogen/1000 sq ft/year will increase disease severity. Nitrogen applications should not be made after early August because this will increase turfgrass susceptibility to cold temperature injury. Application of ammonium sulfate from June to August at monthly intervals (1 lb N/1000 sq ft) may acidify the soil and reduce severity of spring dead spot. Heavy applications of fast-release nitrogen fertilizers should be avoided during the summer following a severe outbreak of the disease. Application of .8 lb of potassium chloride (KCl) at monthly intervals during the summer has also been shown to reduce spring dead spot severity.
Bermudagrass cultivars vary markedly in susceptibility to spring dead spot. Our research indicates that the cultivar Midiron is the most resistant variety. Other Kansas cultivars called Midlawn and Midfield also appear to be somewhat tolerant to the disease. The seeded cultivar ‘Guymon' also shows some tolerance, but this cultivar is somewhat course in texture and is not recommended for home lawns in Kansas. Avoid using Arizona common bermudagrass, U-3, or other varieties adapted to the southeastern United States.
The fungicide Rubigan is the only labeled product for control of spring dead spot in
Kansas. Our results with this fungicide have been erratic. Fall applications of Rubigan
and other experimental fungicides do seem to reduce disease severity and speed recovery of
the turf in the spring, but they do not completely eradicate the disease and therefore are
not currently recommended for routine control of spring dead spot.
References:
1. Spring Dead Spot of Bermudagrass, K-State Research & Extension Plant Pathology Fact Sheet.
Last Update: 01/23/2004
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