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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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Monday - April 01, 2013

From: Katy, TX
Region: Southwest
Topic: Diseases and Disorders, Pests, Trees
Title: Growths on Shumard Red Oak leaves from Katy TX
Answered by: Barbara Medford

QUESTION:

Our beautiful Shumard Red Oak has developed lots of light green grape like growths on the leaves. Please inform us what this could be and how we should treat it?

ANSWER:

Quercus shumardii (Shumard oak) is, according to this USDA Plant Profile Map, native to Harris and Ft. Bend Counties, which means it is growing in the right place.

We learned in this article from Cornell University, Department of Plant Pathology that Quercus shumardii (Shumard oak) can develop oakleaf blister. This is a fungus and red oaks (which the Shumard Oak is) can be most susceptible to it. The pictures in that article don't look much like what you are describing so we will look further.  From Texas A&M AgriLIFE Extension, Texas Plant Disease Diagnostic Lab here is an article on Oakleaf Blister

Insects that attack the Shumard Oak are June beetles, striped oakworms. cankerworms, forest tent caterpillars, yellow-necked caterpillars, variable oakleaf caterpillars and red-hum[ed oakworms. Shumard oak acorns are subject to attack by acorn weevils. If you suspect any of these, you can search on the Internet for any of them for pictures and more information.

However, we suspect oaks galls. Here is an article from the University of Kentucky Extension Service on Oak Galls. It has no pictures at all, so we will try to find more information. From Google, we found Images of Leaf Galls, some of which look very like what you are describing. If you click on one of those pictures it will show you an enlargement, and if you click on it again, it will take you to the website from which the picture was copied.

Since we are neither entomologists nor plant pathologists, we suggest you consult a trained, licensed arborist for what to do next. It could be that, though unsightly, the problem is no serious threat to the tree.

 

From the Image Gallery


Shumard oak
Quercus shumardii

Shumard oak
Quercus shumardii

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