Crape Myrtle Disease: Sooty Mold

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Crape myrtle

Leaf and stem surfaces are covered with a black sooty substance, causing them to appear black and dirty. Sooty mold indicates that there is an insect problem on the plant. These common molds are caused by fungi that grow on the sugary substance, called honeydew, produced by various insects that suck sap from the plant. Aphids, scales, mealybugs, and whiteflies most commonly cause this problem.

Prevention: Sooty molds are unsightly, but are relatively harmless, since they do not directly attack the plant. Controlling the insect problem can reduce excessive amounts of sooty mold. Reduce aphid numbers by allowing beneficial insects, such as lady beetles, to inhabit the plant. Aphids can be removed from the plant with a strong spray of water.

Treatment: Although not necessary, sooty mold can be washed from the leaves by spraying foliage with a dish soap solution (4 ounces per gallon of water), waiting three to four minutes, and then rinsing the foliage with a strong stream of water.

Pest Management

To treat your plant against these pests, spray the leaves with a solution of either horticultural oil or neem oil. Horticultural oil and neem oil are less toxic pesticides that will rid your plant of heavy infestations. Spray in the early evening after the plant is no longer in direct sunlight. Just like tanning oil, neem and horticultural oil can exaggerate the effects of the sun and you run the risk of sun burning the leaves if you apply in full sun. Depending on the severity of the infestation, repeat applications may need to be made every two weeks or so. Always follow the directions when using any pesticide.

Submitted By: Anass Banna, Smalls Farm Agent