Why is so much sap falling from my oak trees this year? It is everywhere — cars, decks, windows, etc.

Gardens & Landscapes January 20, 2012 Print Friendly and PDF

The most likely cause of the dripping sap is aphids. Aphids favor many deciduous and evergreen trees. Aphids are a piercing, sucking insect that feed off the fluids in the leaves and tender stems. They secrete a sticky fluid called honeydew that is a by-product of the tree sap they consume. When the tree is heavily infested, the honeydew can coat the limbs, trunk, and anything underneath the tree. Often, a black, sooty mold will form where this honeydew is secreted. You may want to read the Ohio State Extension publication: Aphids on Trees and Shrubs HYG-2031-90.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.