Kentucky bluegrass and rye grasses often suffer from a yellow/orange fungus referred to as Rust. It is unsightly, but only a real danger to newly seeded lawns in the spring. Shaded areas that feature compact soil which is not adequately fertilized are common locations for Rust fungal growth.

Rust fungus disease

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Courtesy of Howard F. Schwartz, Colorado State University,

Shape: Irregular patches

Season: Summer – over 75 degrees


  • Frequent mowing
  • A morning watering schedule
  • Lawn aeration
  • Removal of grass clippings during mowing

Remedy: DMI and QoI (strobilurin) fungicides can be used to stop Rust infestations quickly when combined with proper turf care.

Rust fungus diseases

What is fungal disease Rust

Rust diagnosing disease

Courtesy of

How do identify fungus Rust

Courtesy of University of Minnesota

Rust is a fungal disease of turf grass. Rust usually attacks turf grass in the late summer or early fall. Usually the disease attacks turf in dry weather conditions or when the soil is low in nitrogen. You can easily identify rust if you pull a couple of blades out of the turf. You will observe orange spots coating the blades; this is an indication that the turf is infected with rust. The disease starts with yellow spots that changes color to orange, red or brown. Gradually the grass patches will become very weak and thin.

The disease can attack turf even in cool nights when rains frequently. Humid conditions along with bright hot sun also favor the formation of spores.  If grass remains wet for more than eight hours, rust can be developed in turf.

The rust disease reduces the ability of grass to photosynthesize s it is recommended to water them early in the day. The grass will have greater chance to dry before intensified sun heat. Remove all the thatch below 1/2 inch.  The grass below a 1/2 inch in the soil reduces air circulation providing ideal breeding area for spores. Soil test before fall is essential before fertilizing. Add nitrogen to soil if needed. You can apply fertilizers until September.

Chemical control for rust should be avoided. However, if necessary, apply fungicide to control the rust disease.

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