How to Manage Pests

UC Pest Management Guidelines

Turfgrass

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.

SUSCEPTIBLE TURFGRASSES

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.

MANAGEMENT

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 Amount to use Ag Use
REI‡
NonAg Use
PHI‡
(Example trade name)   (hours) (days)

UPDATED: 12/16
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees (PDF), and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. AZOXYSTROBIN
  (Heritage) 0.4 oz/1000 sq ft 4 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
B. IPRODIONE
  (Chipco 26019) 8 fl oz/1000 sq ft. See label Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
 
C. MYCLOBUTANIL
  (Eagle 20EW) 1.2–2.4 fl oz/1000 sq ft 24 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
D. PROPICONAZOLE
  (Banner Maxx) 4 fl oz/1000 sq ft 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
E. THIOPHANATE-METHYL
  (Fungo Flo) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
 
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. 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 (REI) 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.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Turfgrass
UC ANR Publication 3365-T

Diseases

A. Downer, UC Cooperative Extension, Ventura County
M. A. Harivandi, UC Cooperative Extension, Alameda 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

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