
nikki-phipps
Certified GKH Gardening Expert
Certified GKH Gardening Expert
Answered on August 1, 2017
This sounds like knopper gall which is due to a wasp. Generally, insect galls will not harm the tree, though the affected acorns will not germinate - but unless you're growing these this shouldn't be much of an issue.
Was this answer useful?
00