Removing sap and honeydew from cars
Parking under large trees often results in a peppering of sticky substance coating the car. Most people assume this is tree sap, but the culprit is far more likely to be insect honeydew, excreted by aphids or -- in some cases -- scale insects, infesting the leaves and branches.
Composed of sugars and other waste products that pass through the insects' bodies undigested, honeydew becomes harder to remove the longer it's left on the car. However, if you remove the honeydew and park under the tree again, you'll just end up with more sticky stuff drizzling down on your vehicle.
You may be able to dislodge and reduce the numbers of offending aphids in the tree by blasting overhanging branches with a forceful stream of water from your hose. A hard stream of water does not help much, however, if the source of honeydew is scale insects.
Spraying with insecticides is rarely needed to protect the health of the tree.
The July 30, 1997 Fixit column in the Star Tribune suggests ways to remove pine pitch from a car. These methods should work equally well on hardened honeydew. Here is that article, by permission:
Question: How can I remove tree sap from my car's exterior?
Answer: Remove pine tree pitch with a wax and grease-removing product. Such products are available at auto supply stores.
Be sure to wash and dry the car before applying the wax and grease remover. Then dampen a clean cloth with the solvent and rub the affected area. It may require several attempts if the sap is very thick or extremely hard. The surface may appear hazy after the solvent evaporates, but a good wax application will eliminate the haze and complete the job.
Or, you can try rubbing alcohol, WD-40 lubricant or Skin-So-Soft bath oil. The way to use those materials is to let them do their work of dissolving (in the case of alcohol) or softening (in the case of oils), enough to rub off the remaining sap. If you use the oil, wash the car afterwards to remove it.