News Article for April 1, 2008:
Crape myrtles are one of the slower trees to leaf out in the spring. I have noticed that most of them have begun to put on leaves now.
I get a lot of calls every year about crape myrtles and the black scaly material all over the leaves. This problem is called sooty mold.
Sooty mold is a fungus that lives readily out in the environment and forms a black crust that can cover the leaves and twigs.
While sooty mold is the problem that you can readily see, it is not the primary problem.
The primary problem is insects, usually aphids. These soft bodied insects feed on the underside of the leaves and suck plant juices. The aphids excrete a high sugar substance that we call honeydew. This honeydew is very attractive to honey bees, wasps, ants and fungi. It is the fungi, sooty mold that grows on the honeydew and covers the foliage and twigs.
To eliminate sooty mold you have to control the aphids. You can control the aphids by spraying insecticides, but that requires multiply applications through out the year to maintain control.
An easy treatment is to use Orthene (75S) as a paste. You can also buy it by its common name which is Acephate.
This technique involves painting the insecticide on the trunk(s) of the tree rather than spraying. When aphid populations are first noticed or about now, it is the time for the first treatment.
Remove any loose bark from the trunk(s). Make a slurry of 4 tablespoons of Orthene (75S) and one tablespoon of water. Using a paint brush, apply a band around the trunk twice the width of the trunk(s) diameter. If your tree has a single trunk that comes up and then has multiple trunks, paint the band around the single trunk just below the branched area.
On trees that are multiple trunked, each trunk should be painted. The band can be painted any place on the trunk above the ground. A second application should be made in late July or early August. This will last the rest of the year.
Orthene is systemic insecticide that is absorbed by the bark and transferred to the leaves through the plant’s circulatory system. When insects feed on the leaves they will get a lethal dose.
This has been by far the most effective and easiest control for sooty mold on crape myrtles.
For more information on these or related topics, contact Kenny at 686-3020.