While these signs may not be life-threatening, invasive insect species can do damage to oaks.
Scale insects on leaves, branches, and bark.
Aphids (small, usually green-horned insects) on the undersides of leaves.
This substance may have turned black and “sooty” from bacteria.
Sticky substance on leaves, plants, and other items beneath the tree.
To determine if your oak is dripping because of insects feeding on your tree, look for the following signs: Sticky “honeydew” and tree sap falling from your oak can be caused by a variety of insect species, including aphids, lace bugs, scale, filbert weevils, and filbert worms. Long story short, if there’s something sticky falling from the branches of your oak, an infestation of insects is the likely cause. The less common causes of oaks dripping tree sap are bacterial wetwood diseases and Sudden Oak Death, which cannot easily be treated.
Dripping sap may be caused by bacterial wetwood infection or Sudden Oak Death in some cases.
Oak may drip sap in summer and fall if insects infest the growing acorns.
Most often, a sticky substance falling from your oak is the excrement of invasive insects feeding on oak sap.
If your oak is dripping something sticky in late summer or fall, it may actually be sap, but this is caused by insects infesting the oak tree’s acorns. If a sticky substance is falling from your oak tree in spring and early summer, it is most likely “honeydew,” which is the nickname for the excrement of insects that have bored into your oak tree to eat its sap. What is the Sticky Stuff Falling from Oak Trees?