Symptoms: This is a name for a shiny, sticky covering that coats leaves and twigs usually later in the summer. It looks as if someone has spread a coat of shiny lacquer on the top surface of the leaves.

Diagnosis: What you are seeing is called "honeydew" which is a strange name for the droppings of sucking insects. Aphids, mealybugs, psyllids, whiteflies and certain scale insects feed on the sap of plants. They run these liquids through their digestive systems and out the other end. The stuff drops from there onto leaves lower on the plant.

A secondary symptom often develops after the honeydew sits on the leaves for a few days. Sooty mold is a black, powdery coating caused by a fungus that grows on the honeydew. It can hurt the plant when it becomes thick enough to block light from penetrating to the chlorophyll in the leaf.


Treatment: To prevent the development of honeydew and sooty mold, you would need to control the sucking insect infestation. Otherwise, honeydew will wash off with the rains or you can try to wash it off with a hose and a stream of water.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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