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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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Saturday - April 30, 2011

From: Austin, TX
Region: Southwest
Topic: Pests, Shrubs, Trees
Title: Holes in leaves of wax myrtle from Austin
Answered by: Barbara Medford

QUESTION:

I just purchased 4 of the 5 gallon Wax Myrtles at the last spring plant sale and after planting them, they are getting eaten by bugs leaving holes in the leaves. I can't find any of the bugs doing the damage. What would be good to spray on these wax myrtles for insect control? Thanks!

ANSWER:

Water. And if that doesn't work, add a little pure liquid soap to the water, and spray again.

Okay, now we've had our fun, we'll get serious. We are neither entomologists nor plant pathologists, but our experience as gardeners tells us this is probably aphid damage. Look on the underside of the wax myrtle's leaves-do you see tiny white specks moving around? Are there ants present? Is there a whitish deposit on those undersides, some of which may be developing a black moldy appearance?

Sooty mold is a fungus, or more commonly a complex of two or more fungal species, that grows on honeydew or on plant exudates. Honeydew is a waste-product of aphids and other plant-sucking insects. As honeydew is excreted by sucking insects, it falls and coats any surface upon which it lands. Sooty mold fungi invade and live upon this sugary coating. These fungi do not infest the leaf ifself. Thus, sooty mold may often be found growing on any exposed surface beneath aphid-infested trees and shrubs. Sooty mold can cause great harm to plants, however, by blocking sunlight to the leaf surface below and diminishing photosynthesis.

Sooty mold can often be successfully removed by rinsing with water from a garden hose. However, this will be most effective after the aphids or other honeydew-producing insects are destroyed. Sometimes sooty mold development is so severe and persistent that only time and exchange of leaves through the growing seasons will remove it all.

Aphids are not especially difficult to control and non-chemical methods are usually very effective. Insecticidal soaps are often the remedy of choice for many gardeners. Various brands of insecticidal soaps may be found at just about any retail nursery or garden center. Be sure to read and carefully follow all label directions when using any pesticide, organic or chemical.

 

 

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