Native Plants

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Monday - April 20, 2015

From: Austin, TX
Region: Southwest
Topic: Pests, Trees
Title: Black Sap from Live Oak in Austin, Texas
Answered by: Anne Van Nest

QUESTION:

We live in South Austin and our neighbor has several beautiful, enormous Live Oak trees whose canopies hang over into our yard. This past week, they've begun dripping some sort of black sap all over our backyard. Is this normal, or some indication of something wrong with the trees? Thank you!

ANSWER:

Most likely your tree has an insect called an aphid feeding on the foliage. Aphids are soft bodied insects and when they are numerous you can see the released sticky "sap-like" substance called honeydew. When the honeydew is numerous and stays on objects or leaves for a lengthy period a black sooty mold begins to grow on the sugary substance. Also bees and wasps are attracted to the honeydew that is being released by the aphids. Have an arborist take a look at your tree to determine if any action is needed. Aphids are a fairly regular visitor to Austin gardens - some years worse than others.

From the University of California Integrated Pest Management Program, here is an article on managing aphid infestations.

Also here's a link to a previous Mr. Smarty Plants question about aphids.

From the Image Gallery

Coastal live oak
Quercus virginiana