Garden & Landscape Tips

Astilbe fried in summer heat
The powdery spores from lawn rust disease often coat shoes, giving rise to the disease’s nickname of “orange-shoe disease.”
George Weigel

 

Have you ever walked across your lawn and noticed that your shoes were coated with some sort of powdery yellow-orange substance. You might have wondered: did somebody spray something? Is it pollen or something dropping out of the air? Maybe bugs? But the answer is none of the above. The mystery is a case of a lawn disease known as rust, and the powdery material is the spores of a fungus that’s causing the disease.

The disease is harmless to people and pets, and it seldom seriously damages lawns. However, it is a nuisance when you track the yellow-orange spores into the house, and it is a lawn stress that can piggyback on other problems to thin a lawn.

Lawns get rusty?

Lawn rust is a fairly common lawn disease that typically springs up in mid to late summer, especially when days are warm and humid, nights are cool and dew-producing, and frequent quick-hit showers keep the grass blades damp.

Lawns that are under-fertilized or otherwise stressed are more prone to rust – and other lawn diseases, for that matter.

Lack of nitrogen – the soil nutrient that grass craves the most – is a leading contributor to lawn rust. Other causes include compacted soil, cutting the lawn too short, and too much shade.

When conditions are right and the fungus is present, the disease starts out with little yellow flecks on grass blades. The flecks then mature and open to release the yellow-orange powdery spores that end up on the surface of passing objects, such as shoes. These spores are what have led to the disease’s nickname of “orange-shoe disease.”

Spores can blow into a lawn with the wind or they can transfer in on things like shoes and lawn equipment.

Close-up view of lawn rust on a blade of grass
The powdery spores emerge from fungal flecks on the grass blades.
George Weigel

What to do about it?

Fortunately, lawn rust usually goes away on its own, and treatment is seldom recommended.

In severe cases or in lawns in which the owner has a low tolerance for even temporary or cosmetic imperfections, several granular lawn fungicides can be used to slow the disease’s progression. However, even fungicides can’t undo the discoloration that’s already happened.

  1. Fertilize the lawn. Given that the main factor in rust’s development is lack of nitrogen, fertilizing a lawn is one of the best things you can do to prevent rust. The end of summer and early onset of fall is a good time to fertilize in most of the country, assuming that the lawn isn’t brown and dormant from drought. For those on seasonal lawn programs, spring, early summer, and mid to late fall are typically good times to fertilize.
  2. Avoid frequent watering. Avoiding frequent light irrigation is another step that homeowners experiencing lawn rust can take. Deeper irrigations once or twice a week will better keep off rust and hydrate the lawn than daily light waterings. Additionally, any watering should be done in the morning rather than the evening so that the blades can dry quickly instead of staying damp all night.
  3. Cut the lawn on a high setting. Cutting the lawn at a higher setting also helps to reduce your lawn’s chances of developing lawn rust.
  4. Purchase high quality, disease-resistant grass seed. If you plan to overseed your lawn, choose a grass seed that’s more disease resistant to ensure that your lawn isn’t susceptible to damage from diseases such as lawn rust. There is an easy way to find out which grass seed varieties are best. An independent organization known as the National Turf Evaluation Program (NTEP) tests and evaluates seed varieties every year. Ratings are based on color, disease resistance, insect resistance, drought resistance, ability to withstand traffic, leaf texture, density, heat tolerance, cold tolerance, and overall turfgrass quality.
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