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Originally published Thursday, May 9, 2013 at 5:04 AM

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Fairy ring puts a bad spell on your lawn; fight rhody mildew with oil

Garden writer Ciscoe Morris discusses eradication of mushrooms in the lawn and treatment of powdery mildew in rhododendrons.

Special to The Seattle Times

Gardening Events

Ciscoe’s Picks

North American Rock Garden Society: Plant hunter Chris Chadwell, proprietor of Chadwell Seeds in England, is the guest. 7:30 p.m. today (May 9), Center for Urban Horticulture, 3501 NE 41st St., Seattle (

Pike Place Market Flower Fest: Flower farmers fill the street from 10 a.m.-6 p.m. Saturday-Sunday at the market, First Avenue and Pike Street (

Mushroom Maynia! at the Burke Museum: Lectures, food, ID sessions, crafts, 10 a.m.-4 p.m. Saturday, Burke Museum, University of Washington, Seattle; $7.50-$10 (

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In the Garden

Q: I have mushroom growing in circular patterns in my lawn. The grass is dying where the mushrooms are growing. Is there something I can spray to rid the lawn of the mushrooms?

A: The bad news is that you have a fairy ring. The good news is that you get to test out a solution I’ve always wanted to try, but have never had the opportunity to see if it works.

Fairy rings are mushrooms that almost always grow in an arc or circle. They kill the turf in the arc because the mushrooms grow so thickly, they outcompete and starve the grass for nutrients and water.

No fungicides are effective against fairy ring. According to research at the University of British Columbia, the only method that works is to remove half of one fairy ring; then till it in with half of a neighboring one.

The mushrooms of fairy rings are mutually antagonistic. In other words, mushrooms from one ring hate the guts of mushrooms from another ring, and if you mix them up together, they go to war. Just remember to mix the mushroom-infested soil from both rings well so there’s plenty of contact.

If all goes well, the warring mushrooms should wipe each other out. Stay out of the way of calvary charges, and send me an email to tell me if it really works!

Q. The foliage on several of my rhododendrons has been thinning out over the last few years and the leaves have yellow see-through spots. Will my rhodies survive?

A. The yellow translucent spots and defoliation are a sure sign that your rhododendrons are infected with powdery mildew.

Usually, plants infected with this are covered in a gray powdery fuzz. On rhododendrons, however, the powdery fungus only shows up on the bottom of the leaves, and sometimes, even when leaves are severely affected, the powdery coating is so sparse, it can’t be seen without a magnifying glass.

Defoliation is a result of this disease, and if left untreated, your rhododendrons could be weakened or even killed by leaf loss. Begin by raking up and disposing of fallen leaves. Remove dead branches and twigs, which can spread the disease.

Several products including horticultural oil are effective at preventing the disease. Neem oil, a vegetative product, is undergoing research to see if it is effective as well. Sprays should begin when the leaf are half-emerged and again as soon as it reaches full size. Further treatments may be required if the disease is severe.

Ciscoe Morris: “Gardening With Ciscoe” airs at 10 a.m. Saturdays on KING-TV.

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About Ciscoe Morris

Ciscoe Morris' column runs Thursdays. His show "Gardening with Ciscoe" airs at 10 a.m. on Saturdays on King 5.

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