WSU Extension

Hortsense

Lawn and Turf : Necrotic ringspot
(revision date: 1/22/2016)


Biology
Necrotic ringspot (NRS) is a fungal disease primarily occurring on Kentucky bluegrass in central and eastern Washington and Oregon. It is most common on 2- to 5-year-old lawns grown from sod. Infection occurs during early spring, late summer, or fall. The grass develops small (2"-5"), circular, yellowed areas with reddish-brown margins. These can expand to up to several feet in diameter. Roots are damaged and the infected patches lift easily from the soil. The grass often regrows in the center of the patches, leaving the dead rings characteristic of the disease. NRS can be seen throughout the growing season and causes a chocolate-brown discoloration of the roots and rhizomes not seen in similar patch diseases. NRS may superficially resemble Fusarium patch or yellow patch, both of which occur in fall and spring. NRS may also be confused with fairy ring.
Management Options

Non-Chemical Management
  • Plant cultivars which have shown less susceptibility to NRS.
  • Provide proper culture, including adequate, balanced fertilization and deep, infrequent watering.
  • Avoid practices which favor disease such as excessive or insufficient nitrogen, excessive watering, heavy shade, and incorrect mowing heights.
  • Water in the morning so grass can dry quickly.
  • Mow at recommended height.
  • Remove thatch and aerify as necessary.
  • For more information see EB0482E, Home Lawns and EB0713, Diseases of Turfgrass.
Select non-chemical management options as your first choice!

Chemical Management

Fungicides may be used with cultural practices in an integrated approach. Research in the Pacific Northwest has shown that one or two applications of DMI-type fungicides, such as the ones listed below, effectively control the disease when the equivalent of 0.5 to 1 oz. active ingredient is applied per 1,000 sq. ft. in late April or May. Label rates for home garden fungicides would require multiple applications during a six-week period for effective control of this disease.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.
  • ferti-lome F-Stop Lawn & Garden Fungicide RTS
    Active ingredient: myclobutanil  |  EPA reg no: 7401-505
  • ferti-lome Liquid Systemic Fungicide II R-T-Spray
    Active ingredient: propiconazole  |  EPA reg no: 53883-184-7401
  • Spectracide IMMUNOX Multi-Purpose Fungicide Spray Conc
    Active ingredient: myclobutanil  |  EPA reg no: 9688-123-8845
  • This list may not include all products registered for this use.
Images
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Caption: Necrotic ring spot
Photo by: R.S. Byther
Caption: Necrotic ring spot
Photo by: R.S. Byther