NOT A TA
Veteran Member
You'll want to interrupt the life cycle of the aphids that are excreting on your car (or keep cleaning the car). Depending on how quickly you want it to stop and budget that might involve neem oil or insecticidal sprays or something as simple as changing the local environment where they overwinter. Aphids can produce 100 more aphids in as little as 4 weeks during the growing season so if it's bad now it may get much worse. There are a couple different types of aphids that use oaks as hosts depending on the variety of oak and part of the country.