Rust Disease in Lawns

Our turf grasses are prey to numerous disease and pest infestations. One fungal disease called rust, occurs almost exclusively on Kentucky bluegrass and perennial ryegrass.  Although it is mostly a cosmetic issue, the easily dislodged orange spores can be a nuisance by covering shoes, pets and lawn equipment with a rusty residue.

Rust infected grass looks like it has a yellowish-orange hue. When grass blades are inspected closely, they will be coated with yellowish-brown to orange-red spores or dust and can be easily rubbed off with a finger. These spores, carried by the wind, shoes or equipment, spread the disease to other areas during the growing season.

Outbreaks of this disease are most common in late summer and early fall.  Low fertility (in particular nitrogen) and low water availability slow down turf growth allowing rust to develop. Formation of the spores also often occurs during seasons with excess rain which can lead to depletion of available nitrogen. Warm, cloudy, humid conditions followed by bright hot sun also contribute to the formation of rust spores.  Rust outbreaks require moderate temperatures (50 to 60 degrees F) and long evening dew periods (more than 10 hours).

Rust can be managed with attention to plant nutrition and regular mowing habits.  Apply small amounts of nitrogen fertilizer (two tenths to half a pound per 1,000 square feet) in chronic trouble spots (shaded and possible compacted areas) to help control the disease.  The nitrogen will promote leaf growth and allow for regular mowing, which helps the turf outgrow rust’s rather slow infection cycle.  Avoiding irrigation during the early evening will help limit disease spread by lessening the chance of extended dew periods.  It also never hurts to have a soil test done, paying attention to phosphorus and potassium levels.

When cultural practices fail to quell an outbreak, a single application of a fungicide can be used.  For the best result it is recommended that a professional lawn care service be used.

As always, Happy Gardening!

More information about gardening and related subjects can be found online. The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.

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