Sap from my oak trees

Asked July 15, 2017, 10:10 PM EDT

My oak trees have been leaving sap on my car. Usually this happens in the spring but has continued into July. Is there something wrong with them?

Washington County Minnesota trees and shrubs

1 Response

Thank you for your question. In the absence of other symptoms such as cracks or decreased canopy, 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 following links to confirm that this is the problem and get ideas on how to control the problem. http://www.extension.umn.edu/garden/insects/find/aphids-on-deciduous-trees-and-shrubs/ http://ohioline.osu.edu/factsheet/HYG-2031-10