Crepe Myrtles and Sooty Mold
Lots of calls regarding the conditions of Crepe Myrtles and black materials coating the trunks of these trees have been received at the AgriLife Extension office over the last few weeks. What is this material, why is it covering my tree, and will it harm or kill my trees? These seem to be the most commonly asked questions about Crepe Myrtle Tree and the issues right now plaguing these common landscape trees.
Crepe Myrtle trees that are coated in a sticky black material are suffering from issues with sooty mold. This is a name given to a condition that is not truly a disease, but a black coating on leaves, trunks, branches, and fruit that is comprised of a fungal growth. This fungus is usually dark in color and sometimes has a powdery-like appearance hence the name sooty mold. This fungi is saprophytic, meaning that it does feed off the plant or its tissue, but instead thrives on insect secretions from aphids, scale, white fly, and other insects that have a large sugar content. This secretion is known as Honeydew. Under proper conditions, plants may be covered with sooty mold, thus causing concern for homeowners.
Control for sooty mold starts with insect control first. Elimination of insects causing honeydew buildups will eliminate the sooty mold as a secondary issue. There are several options for control of sooty mold in crepe myrtles trees.
The first option is the use of an Acephate-based product. This is a soluble powder that mixes well with water. A combination of 4 parts Acephate and 1 part water can be made to create a paste in a disposable container that can be applied at the base of tree coating each trunk of the tree in a 4” band around each trunk. This systemic insecticide will work its way into the leaves and twigs discouraging insects chewing on tree leaves and surfaces. Reapplication of products will be needed once or twice a year to help control insect populations.
Other options include the use of soil drench type products such as systemic Imidacloprid based products. This product is mixed with water and poured around base of the tree for roots to absorb and be taken into plant systems. Early season applications can be made with products giving an extended period of protection from insects. These products will usually last from 60-90 days, giving longer periods of insect resistance. Reapplication may be necessary for continued coverage.
Spraying the tree’s surfaces with an insecticidal soap can also help to loosen the sooty mold from the tree’s surfaces, but elimination of insects will help to minimize the honeydew created by the insects.
If immediate cosmetic relief from the sooty mold is needed, homeowners may choose to wash trees with a mild soap/water solution to help dislodge some of the sooty mold from the tree trunks. Use of a soft bristle brush is suggested as not to damage tree surfaces and bark. Never use high pressure water or similar to “clean” tree as damage may occur to bark surfaces.
With a little work and effort, your crepe myrtles trees can be restored to the full glory and bloom during the summer months with shows stopping blooms.
For questions:
David Oates
CEA-Horticulture Jefferson County
Texas A&M AgriLife Extension Service
409 835 8461
David.oates@ag.tamu.edu
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