Dr. Pete's Turf Tips
Peter H. Dernoeden, Ph.D.
Rust (several Puccinia spp.) mostly is a problem in Kentucky bluegrass, perennial ryegrass, some zoysiagrass cultivars, and is a growing problem in tall fescue. Rusts are especially damaging to turfs grown in shaded environments. If there is an extended period of overcast weather, however, rust can debilitate and thin turf in open areas. The result often is more weeds.
The disease appears as days grow shorter in the autumn. As noted below, rust fungi live indefinitely in infected plants, but only show their signs and symptoms in early-to-mid-autumn, when spores are produced. Rust infections give turf a yellow or orange appearance from a standing positon. On close inspection, small, yellow, orange or brick-red-colored pustules can be seen on leaves. Huge numbers of spores are produced within each powdery pustule, which spread the pathogen. Sporulation can be so massive that spores turn shoes a rust or yellow color.
Rusts are highly sophisticated obligate parasites that live and reproduce in living tissues only. Rusts have a complicated lifecycle, and being obligate parasites, they do not usually kill turf since the fungus requires living plant tissue within which to survive and reproduce. The disease only becomes noticeable when the fungus produces spores. During most other times of year, rust-infected plants appear amazingly healthy. Spores are produced below the epidermis in pustules, which eventually burst through leaf surfaces. The release of spores damages leaves, which soon turn yellow or orange in color and die. Stems are not affected and plants will survive if properly managed. Rust is disfiguring, weakens plants and predisposes them to other stresses. Furthermore, thinning of stands is common, thus inviting weed invasion, especially winter annuals. After spore production has ended in severely infected stands, turf appears, brown, unthrifty and severely thinned.
A good fertility and weed control program will eventually revive turf, but if left untreated, rusts will eventually severely debilitate and ruin turf. Rust fungi are easily controlled with a single application of a DMI/SI fungicide (e.g. Banner MAXX, Bayleton, Eagle, Trinity, Triton, Tourney, Torque, and others).