How to Manage Pests
UC Pest Management Guidelines
Spring Dead Spot
Pathogens: Ophiospharella korrae (=Leptosphaeria korrae) and O. narmari (=L. namari)
(Reviewed 9/09, updated 9/09, pesticides updated 12/16)
In this Guideline:
DESCRIPTION OF THE DISEASE
Spring dead spot appears as circular areas of dead grass, 6 to 12 inches in diameter when turf resumes growth in spring. The spots may coalesce to form large areas. On affected plants dark elliptical sclerotia are often visible on stolons. Dark sunken lesions can be seen on affected crown buds, roots and stolons; these areas may become black, necrotic, and brittle in advanced stages of infection. Sometimes, the symptoms are not evident until 2 or more years after the establishment of the disease. Overseeding bermudagrass with another turf species may mask the symptoms of this disease.
Bermudagrass is susceptible to spring dead spot.
CONDITIONS FAVORING DISEASE
The pathogen survives in debris (old thatch and roots) as fungal threads and sclerotia, which are tiny, hard, often dark, resting bodies. Spring dead spot is spread by sclerotia and infected plant parts, as well as through infested sod. Initial infections of new tissue begin in late summer or fall when air temperatures range between 70° to 75°F. When the bermudagrass goes into dormancy (daily air temperatures of 50° to 60°F or lower), the fungus continues to colonize and kill the affected tissue. Damage to the affected plants is usually only visible when the bermudagrass emerges from dormancy.
The focus of a spring dead spot management program should be exclusion of the pathogen from new plantings and promoting strong, healthy turf and root systems that can tolerate and recover quickly from the damage caused by the fungus. Proper irrigation and fertilization are important in the management of this disease. Spring dead spot is difficult to manage with fungicides.
Establish new turf plantings with clean sod from areas where spring dead spot has not been a problem. Irrigate according toevapotranspiration needs of the turfgrass. Dead grass can be raked out and replanted with new bermudagrass seed or stolons; alternately, bermudagrass can be overseeded with ryegrass in fall or winter to hide disease symptoms in spring.
Thick thatch and low mowing heights favor the development of the disease. Manage thatch and keep it less than 0.5 inches thick with regular dethatching and aerification. Provide adequate irrigation based on evapotranspiration needs to promote vigorous growth during summer months and reduce drought stress damage. Raise mowing height in late summer or early fall to reduce pre-dormancy stress.
Maintain adequate levels of potassium in the soil and apply potassium fertilizers in fall to promote winter hardiness. Use adequate nitrogen fertilization programs in spring and summer, but minimize nitrogen applications in late summer and fall. Late summer and fall applications may contribute to disease severity because the added nitrogen promotes the growth of leaves at the expense of roots and may delay the bermudagrass from entering dormancy, resulting in both a reduction in cold hardiness and carbohydrate reserves. Loss of carbohydrate reserves is detrimental to plants when they are emerging from dormancy in spring. Use ammonium-based nitrogen sources versus nitrate- or urea-based fertilizers. Maintaining a low soil pH (5.2 to 5.3) appears to reduce the severity of the disease.
Once established, spring dead spot is a difficult disease to control with fungicides. Best results are usually seen when a combination of cultural and chemical control methods is used. Make one or two fungicide applications beginning in the late summer or early fall using enough water volume to get the fungicide into the root zone.
UC IPM Pest Management Guidelines: Turfgrass
A. Downer, UC Cooperative Extension, Ventura County
Acknowledgment for contributions to Diseases:F. Wong, Plant Pathology, UC Riverside
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside