Aphid Honeydew on Red Oak: The Real Cause of "Sap" Dripping

Diagnosis

"Sap" dripping on driveway and cars from a 13-year-old red oak in zone 8b is almost certainly aphid honeydew. Aphids feed on leaf phloem and excrete sugar-rich liquid; sooty mold grows on it, blackening leaves.

Solution

1. Systemic insecticide: Imidacloprid (Merit) soil drench or trunk injection—translocates to leaves, kills aphids for a season.
2. Foliar spray (alternative): Insecticidal soap, horticultural oil, or pyrethroid for immediate knockdown.
3. Timing: Apply at bud break or first sign of aphids.

Result

Controlling aphids stops the honeydew (and sooty mold) completely. The oak itself is not "weeping sap."