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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)

In this Guideline:


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.


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.

Cultural Control
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.

Treatment Decisions
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.

Common name Example trade names Ag Use
NonAg Use
(trade name)   (hours) (hours)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a fungicide, consider general properties as well as information relating to environmental impact.
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11) 4 until dry
B. FENARIMOL Rubigan  
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 12 until dry
C. IPRODIONE Chipco 26019  
  MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2) see label until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 24 until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 24 until dry
F. THIOPHANATE-METHYL Fungo 50, T-Methyl E-Pro  
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1) 12 until dry
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Turfgrass
UC ANR Publication 3365-T
F. Wong, Plant Pathology, UC Riverside
M. A. Harivandi, UC Cooperative Extension, Alameda County
Acknowledgment for contributions to Diseases:
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside

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