>Growths on acorns are typically caused by gall wasps, most commonly the knopper gall wasp (Andricus quercuscalicis), which lays its eggs in the developing acorn buds of Pedunculate Oak.
>This induces the tree to form abnormal, knobbly, bowl-shaped galls that start as sticky, red growths in August and later turn woody and brown.
>These galls serve as a protective environment for the wasp larvae, which feed on the host tissues, but the damage to the tree is minimal and does not threaten its overall health.