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.