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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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Thursday - May 01, 2014

From: Houston, TX
Region: Southwest
Topic: Non-Natives, Diseases and Disorders, Pests, Transplants, Shrubs
Title: Problems with non-native Banana Shrub from Houston
Answered by: Barbara Medford

QUESTION:

My 7' beloved Banana Shrub (magnolia) has white dots on top of the leaves and nasty black stuff covering the backside of the leaves. The plant is dropping leaves. What can I do to save it? I has been in a big pot for 13 years and when I saw the white spots and black nasty stuff last week, I transplanted the root bound tree into the ground where it will get more sun. I pulled open the roots and cut them as best I could. I have been spraying and wiping the leaves, top and bottom with Palmolive dish soap in water for three days now. But the tree looks very sick. Please, please help. Madalene Hill of Festival Hill in roung Top gave me this tree 13 years ago so it is very dear to me.

ANSWER:

We were very confused when you referred to your plant as a Banana Shrub (magnolia). Here is information we got from Wikipedia:

"Magnolia figo (also called Banana Shrub, Port Wine Magnolia, Michelia figo) is an evergreen tree growing to 3-4 m tall. It is native to China. Susceptible to black soot."

The Lady Bird Johnson Wildflower Center is dedicated to the growth, protection and propagation of plants native not only to North America but also to the area in which those plants are being grown; in your case, Harris Co., TX. That is what confused us, we knew that Banana Shrub was not in our Native Plant Database but magnolias are native to North America and, in fact, Magnolia grandiflora (Southern magnolia), is native to Harris County.

Magnolia figo, alas, is not, but is native to China. This puts it out of our area of expertise; however, we might be able to make a couple of suggestions as to what is wrong. The first thing that comes to mind is aphids - they are small white bugs, and deposit aphid poop on the bottom side of leaves of affected plants, which then turns a moldy black. Check out this article from the University of California Integrated Pest Management on what that pest looks like and how to deal with it. The article from Wikipedia also mentioned "Susceptible to black soot." When we searched the Internet on "black soot plant disease" we got this article from Gardening Know How on Sooty Mold. When we read that article it sounded a whole lot like aphids, again, were causing the problem. Hopefully, from one or the other you will get help for your plant.

 

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