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How to Manage Pests

UC Pest Management Guidelines

Circular spots in annual bluegrass caused by Fusarium blight.


Fusarium Blight

Pathogens: Fusarium culmorum, F. tricinctum

(Reviewed 9/09, updated 9/09)

In this Guideline:


Fusarium blight first appears as small, circular, grayish green areas, ranging from a few inches up to a foot in diameter. Some plants in the center of the circles may survive, giving them a frog eye or donut appearance. The crown or basal area of the dead stems is affected with a reddish rot and is hard and tough. At times, a pink layer of the fungus can be seen near the soil line. The dead foliage appears bleached. The fungus survives as mycelia in plant debris and plants killed by previous infections, or as thick walled resting spores (chlamydospores) in the thatch and soil.


Fusarium blight can affect a number of cool season grasses grown in warm weather conditions including bentgrasses, red fescue, tall fescue, perennial ryegrass and centipedegrass, but is most severe on Kentucky bluegrass. For Kentucky bluegrass, the most susceptible cultivars are Park, Campus, Fylking, and Nugget. A-34, Baron, Merion, Victa, Windsor, and the newer cultivars such as Adelphi, Bonnieblue, Geronimo, Majestic, Parade, and Rugby, are much less susceptible.


The disease is favored by daytime temperatures of 85° to 95°F and night temperatures of 70°F or above.


Fusarium blight occurs most commonly in areas that have been stressed for moisture and in areas in full sun. Follow proper irrigation and fertilization practices and regularly dethatch the turfgrass. Fungicides may be required if the turfgrass has a history of fusarium blight, but complete control is difficult to achieve with fungicides.

Cultural Control
Follow recommended irrigation scheduling practices based on evapotranspiration need of the turfgrass to avoid moisture stress. Because the disease is also worse under excessive nitrogen, recommended fertilization practices should also be implemented. Use 20% perennial ryegrass when seeding bluegrass, and choose resistant varieties. Low cutting heights on golf courses may worsen infestation, as well as excessive thatch.

Treatment Decisions
The crown and basal rot associated with fusarium blight is difficult to control with fungicides. If using fungicides with little or no systemic activity (iprodione), apply them preventively when environmental conditions favor the development of the disease. Systemic fungicides can be used either at this same time, or soon after symptoms begin to appear.

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

Calculate impact of pesticide on air quality
When choosing a fungicide, consider general properties as well as information relating to environmental impact.
A. FENARIMOL Rubigan  
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 12 until dry
B. IPRODIONE Chipco 26019 see label until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 24 until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 24 until dry
E. THIOPHANATE-METHYL Fungo 50, T-Methyl E-Pro  
  MODE OF ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1) 12 until dry
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3) 12 until dry
  COMMENTS: Provides the most effective control.
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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