Rust in Turf

By John Wilson, Extension Educator

Have your shoes turned rusty-orange after walking across the lawn? If so, your lawn is affected by a fungal disease called rust. Rust may appear at any time during the growing season, but is most common in late summer and is often more severe in shaded areas. It appears during warm, humid, dry periods when the grass is growing slowly and nights are cool with heavy dews.

There are many different rust fungi that can infect lawn grasses, but they all produce the reddish, yellowish or orange spores that give “rust” its name. Rust is most common on Kentucky bluegrass and perennial ryegrass, but can also infect tall fescue lawns.

            Turf rust is easy to identify by the orange pustules on the surface of the leaves. Infected areas of lawn take on a generally yellow appearance with an orangey cast. Initial sites of infection on leaves are light yellow flecks that soon enlarge to form round to elongated pustules that rupture through the grass blade to release the powdery spores.

A single pustule or spot on the leaf may contain 50,000 or more spores, each capable of producing a new infection. The spores easily rub off on shoes, clothing, animals, mowing equipment or other objects that pass through the infected areas and may also be moved around by wind and rain. If a spore lands on susceptible leave tissue and sufficient moisture is present, it will germinate and penetrates into the blade of grass to create a new infection site.

The orange color is caused by the rust pustules and their powdery spores. In a week or two, new pustules and spores appear. Several cycles of infection and spore release may occur during summer and fall until it gets too cool for fungal growth. The fungus may overwinter here, but spores blowing in from the southern U.S. are usually the most important source of new infections.

Turf rust rarely kills the grass, but it does stress plants. Thin stands and weak grass are more susceptible to other diseases, winter-kill, and invasion by weeds. Newly seeded lawns are more heavily impacted by rust than are well-established lawns. There are many grass cultivars resistant to rust. When reseeding or overseeding an area, select and plant a rust-resistant cultivar.

            If you have rust in your lawn, it generally doesn’t require a fungicide treatment. Promoting good turf health usually will keep rust in check. If you haven’t done so already, now is the time to fertilize your lawn, but don’t overfertilize it. One-half to one pound of actual nitrogen per 1,000 square feet of turf is adequate until you make your final application of fertilizer in late October.

If you missed the recent rains, water your lawn to promote growth and to move the fertilizer into the root zone. Water established lawns deeply and infrequently during dry periods to keep the grass growing. Water early in the day so the lawn will dry out and not have water remaining on the leaf surface for long periods of time. Rust and other fungal diseases need moisture on the leaf blade to get established and infect the plant.

If you can keep the turfgrass growing vigorously, it will be mowed before spores can be produced. Mow regularly at the height recommended for the type of grass you have. My mower is set on the highest possible mowing height and I never lower it. Normally I recommend mulching your clippings, but if you have rust on your turf, collect and dispose of infected clippings. The rust infection will eventually disappears with more vigorous turf growth and when the weather turns cold.

For more information about rust in turf, contact your local Nebraska Extension office.