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Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

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Thursday - June 13, 2013

From: Austin, TX
Region: Southwest
Topic: Non-Natives, Diseases and Disorders, Grasses or Grass-like, Trees
Title: Brown rings on grass under live oaks in Austin
Answered by: Barbara Medford

QUESTION:

There are brown rings in the grass at the dripline on several Live Oak trees in our neighborhood. What causes this? The trees appear healthy.

ANSWER:

You did not say what grass you or your  neighbors have. The rings might be a problem in the grass rather than originating from the tree. We will investigate brown rings in non-native grasses bermudagrass, St. Augustine and zoysia.

Although no grasses do well under trees, oak trees have more of an influence on the grasses. Oak, walnut, pecan and other trees exhibit allelopathy which means they exude substances harmful to competitive plants beneath them. Here is a a previous Mr. Smarty Plants answer on how we feel about lawns under trees. Between the shade, the allelopathy and the competition of extensive root systems for water and nutrients, grass growing under trees is always difficult. Since all three of the grasses we mentioned above are non-native to North America we don't know much about them, but will try to find some research to help you make a diagnosis.

Bermuda Grass: From WalterReeves.com Bermudagrass diseases - brown patch.

Zoysiagrass: From Missouri University - Issues of Zoysiagrass Lawns

St. Augustine Grass: From Cypress Isle (FL) Master Gardeners- St. Augustine Grass, Common Summer Problems.

Of course, if you are growing Bouteloua dactyloides (Buffalograss) or Habiturf they both need at least 5 hours a days of sun and won't be growing under the trees anyway.

 

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