How to Manage Pests
UC Pest Management Guidelines
Necrotic Ring Spot
Pathogens: Ophiospharella korrae (=Leptosphaeria korrae), O. namari (= L. namari)
(Reviewed 9/09, updated 9/09, pesticides updated 12/16)
In this Guideline:
DESCRIPTION OF THE DISEASE
Necrotic ring spot appears as large, ring-shaped patches that often cause depressions in the turf. Rings may vary from a few inches to several feet in diameter. Individual plants appear to have drought stress and can be stunted or discolored red, yellow, or tan. Lower stems and roots are often covered with black runner hyphae, and in advanced stages, the affected tissue (roots, rhizomes, and crowns) may turn necrotic and black or brown. Dark fungal structures (hyphae and pseudosclerotia) may sometimes be visible on affected plant parts. The fungus survives as mycelia in plant debris and in the thatch layer. The disease can also be spread by mechanical equipment and infested sod.
Fine fescues and bentgrasses. On bermudagrass, the pathogen causes a disease known as spring dead spot.
CONDITIONS FAVORING DISEASE
Necrotic ring spot development is favored by cool, wet conditions in spring and early fall. Drought stress and high compaction can intensify symptoms later in the season.
Follow good management practices; systemic fungicides have proven effective when applied on a preventive basis.
Maintain the highest mowing height possible to help prevent the development of this disease. Follow recommended irrigation practices to avoid drought stress. Avoid excessive nitrogen fertilization. Resistant varieties of Kentucky bluegrass are available. Replant with other species such as perennial ryegrass or tall fescue.
In areas where necrotic ring spot occurs frequently, began treatment of spring infections when soil temperatures reach 60°F and continue until environmental conditions are no longer favorable for the disease in summer. Apply fungicides in an adequate volume of water, or apply enough water after application, to allow the fungicide to penetrate 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