Rust diseases of lawn grasses

Have you ever walked through your lawn and noticed slight orange or reddish-brown patches that look like rust? As crazy as it sounds, it might actually have been rust. Not the same kind you would find on your metal patio furniture or your car, but one that can be destructive.

Rust is a fairly common lawn disease caused by fungus. It usually shows up from mid-summer through late fall, once the growth of your grass has slowed. Typically, rust shows up when lawns are thirsty, cut too short, or haven’t been fed in a while.

Hot, humid weather with frequent, light showers and long hours of morning dew are ideal conditions for this disease. Depending on your grass type and weather conditions, rust can be either a minor nuisance or a turf-killer.

The fungi symptoms of this lawn disease begin as tiny yellow spots on the grass blades. These spots become elongated and eventually rupture into clusters of rust-orange spores that give the disease its name.

There are many different rust fungi that can infect lawn grasses, but they all produce red, yellow or orange spores. When touched, the powdery, dust-like rust spores leave a color a lot like the fine particles of rust from metal.

Rust spores are tiny and very light weight. They can be carried long distances by the wind, or even collect on lawn mowers, shoes, clothing and animal’s paws; this means even the best kept lawns can be infected. Usually, grasses with a fine texture and deep color, like perennial ryegrass and Kentucky bluegrass, are the most likely victims of rust lawn disease.

Rust that is not treated can quickly thin and destroy good turf, and it is especially dangerous to new seed.

Here are some things to consider when trying to treat or prevent this disease:

--Water your lawn deeply and infrequently. The best time to water is early in the morning so it can penetrate into the root system throughout the day. Watering in the evening increases the moisture in lawns, which encourages diseases.

--Oftentimes, rust is caused from lack of nitrogen. Apply an adequate amount of nitrogen fertilizer.

--Mow frequently and remove the clippings.

--Apply a fungicide containing chlorothalonil. Repeat this application every 7 to 14 days until the lawn is free of rust.

Though rust is not harmful to either animals or humans, try to keep them from walking through infected areas to prevent the spread of this disease and to prevent the unpleasant appearance.

For more information, visit www.extension.

umn.edu/garden/.

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