Rust is a fungal disease caused by several species of Puccinia. All turfgrass species are susceptible to rust. However, it is most commonly seen on perennial ryegrass and Kentucky bluegrass.
From a distance, rust infected turf has a yellow-brown color. Close examination of rust-infected grass blades reveals numerous yellow-orange pustules. Rust can be easily diagnosed by walking across the lawn. As one walks across the lawn, bright orange spores of the rust fungus rub off onto one’s shoes.
Rust most often occurs in mid to late summer. Slowly growing grass is most susceptible to rust infections. Poor turf growth may be due to drought, high temperatures, low fertility, or a low mowing height. Warm days, moderate night temperatures, high humidity, and heavy dews provide favorable conditions for rust infections.
Rust is annoying, but it rarely kills established lawns. The damage is mainly cosmetic. New spring-seeded lawns are most likely to be seriously damaged by rust.
Rust usually fades away (by itself) when the grass begins growing more rapidly with favorable weather conditions. Gardeners can promote turfgrass vigor by fertilizing in September and watering deeply once a week during dry periods. Water in the morning. Morning irrigation allows the grass blades to dry quickly, thereby discouraging rust infections. Mow the lawn frequently. In most situations, fungicide sprays are not necessary.
When establishing a lawn from seed, select a high quality seed mix. Inexpensive, poor quality seed mixes often contain grass cultivars that are highly susceptible to rust.
Turfgrass infected with rust has a yellow-brown color from a distance. Photo by Nick Christians.
Yellow-orange, spore-filled pustules cover rust-infected grass blades. Photo by Nick Christians.