Willow Oak Leaf Distortion: Curling and Midrib Damage

A 50-year-old willow oak shows distorted, curled leaves on several branches. The undersides have a ¼-inch green strip running the leaf length, including the midrib, while the upper surface appears to have the midrib "cut out," leaving a gully. Leaves are leathery with no other spots. The issue appeared suddenly, six weeks after an arborist visit for deadwood removal. The tree stands 85 feet tall and is a prized specimen.

Sudden leaf distortion with midrib abnormalities strongly suggests insect activity. Likely culprits include:

• Gall midges or gall wasps—lay eggs in developing leaves, causing curling and tissue deformation around the midrib
• Leafminers—larvae tunnel between leaf surfaces, sometimes following the midrib
• Aphids or psyllids—feeding on young leaves causes curling and stunting

Nutritional stress typically causes more uniform symptoms (chlorosis, necrosis) rather than the precise midrib alterations described. Collect fresh affected leaves—including the curled portions—and submit them to your county extension office. Their entomologist can identify the pest and recommend targeted treatment if warranted. Early intervention preserves tree health and prevents spread.