Black soot mold can be controlled

Published 7:00 am Tuesday, July 15, 2014

The appearance of a black, powdery coating on the leaves of crape myrtles, azaleas, camellias, laurels, gardenias, and other ornamental plants is a sure indication of sooty mold fungi.

Sooty molds have an alarming appearance but generally don’t cause any real damage to affected plants. Sooty molds are composed of several fungi, which develop on leaves and twigs, typically starting in the early summer.

The mold growth is confined to the plant surface, and the food supply for sooty molds is from honeydew excreted by such insects as aphids, white flies, scales, and other insects which suck sap from their host plants.

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As these insects feed on leaves and tender new growth, honeydew is a byproduct of the feeding process, and this material is deposited on leaves and other plant parts.

Since honeydew is sugary, the material is a perfect food source for sooty mold fungi. When populations of sucking insects buildup on such plants as crape myrtles, mold growth often becomes quite heavy and may cause the plant to have a black appearance.

Often plants growing beneath pecan, hickory, tulip poplar, and other trees, are affected by sooty mold, since these trees are often colonized by aphids and other sucking insects. The honey dew drips down onto landscape plants beneath these trees, and thus are colonized by sooty mold.

The fungi that cause sooty mold do not attack the plants directly, but derive their nutrients directly from the honeydew.

Although sooty molds do not feed on the plants, they can destroy the beauty of the plant if the concentration of the mold is heavy enough to shade out light causing the plants to be yellowed and stunted.

These fungi will also grow on honeydew on walls, sidewalks, fences, automobiles, or anything on which the honeydew is present.

The control of sooty mold is indirectly achieved by controlling the insect that produces this sugary-like material.

There are several insecticides or combinations of insecticides available to control these sucking insects. Care should be exercised to be sure that the one selected is recommended for use on the plant that is to be treated. These insecticides may have to be applied periodically throughout the growing season, depending upon the insects to be controlled and the plant on which they are feeding. Follow label directions carefully as to the use of these materials.

Once sooty mold has become established, it is not easily removed.

The best method to remove this material is to soak affected plants in a water and detergent mixture.

This can be achieved by using one tablespoon of household liquid detergent per gallon of water and spraying on these plants. Wait 15 minutes and wash this material off with a strong stream of water from a garden hose.

This may have to be repeated in several weeks.

Once this has been accomplished, then the procedure should be started for the control of the insects.

Generally speaking, the mold will gradually disappear after the insects have been controlled.


By Eddie Smith