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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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Tuesday - October 27, 2015

From: Center Point, TX
Region: Southwest
Topic: Diseases and Disorders, Herbs/Forbs
Title: What is the black stuff growing on my thoroughwort?
Answered by: Jimmy Mills

QUESTION:

What is the black stuff on my thoroughwort plant's leaves that is killing the plant?

ANSWER:

There are several species of plants that have the common name of thouroughwort, and I suppose most of them are susceptible to this “black stuff” that is probably an infection of sooty mold.

The sooty mold is a fungus that is living on the honey dew on the leaves which is excreted by aphids and other sap-sucking insects living on the plants such as scale. As honeydew is excreted by the sucking insects, it becomes airborne and falls and coats any surface upon which it lands in the area.

I'm including three links that will tell you more about aphids, honey dew, and sooty mold.

aphids, UC IPM

Sooty mold, UC IPM

Sooty mold, USDA

 

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