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
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.