What Is the Yellow Dust on My Lawn?

Disease Identification

• Lawns are prone to the fungal disease called rust. Though a number of different fungi such as Puccinia spp. are likely to cause rust, all produce similar symptoms. The disease gets its name from the characteristic yellow, red or orange powdery spores on the grass blades that often get on clothing, shoes and lawn mowers.

Symptoms

• Early signs of rust include a yellowish green cast on healthy grass growing in shaded landscape areas. Close inspection of the grass shows yellowish-orange pustules on the grass blades. These spores are easily dispersed by wind to other healthy grass areas. In cases of severe infection, grass starts to yellow, wither and die. Rust-infected grasses grow weaker and more prone to numerous other disorders such as winter kill.

Favorable Conditions

• Slow-growing, less vigorous grasses are more prone to rust infections. The disease commonly afflicts grasses during late summer and early fall. Lawns that are suffering from drought stress or are growing in poorly fertile soil, shade or compacted soil are highly susceptible to rust infections. Rust spores are most active during temperatures of 50 to 60 degrees and extended dew periods of over 10 hours.

Management

• Keeping lawns healthy is the primary line of defense against rust infections. Do not irrigate lawns during early evening as this extends evening dew periods. Apply up to 1/2 pound of nitrogen per 1,000 square feet in poorly growing spots during late summer to boost growth. Though fungicides are not generally recommended for disease control, the use of strobilurin is effective on severely affected, well-established grasses. Use fungicides only after cultural control options have been ineffective in controlling the disease.