leaves on oak falling off

[hedgesparrow]

did post in the poorly tree section but no response. have some small oaks and on one the leaves have curled turned brown and fallen off. the whole tree is infected and on looking found a small aphid like creature on leaves silvery grey colour the others have it but not as bad. will try and download the photos if i can any ideas and will it effect the health of tree it is on the boundary of property and overhangs there garage. if it will effect tree what is the best thing to do. if you say it needs taken out then going to be a hole in hedge

[woodyguy]

More likely to get a response if you upload promised photos. Generally oaks can lose all of their leaves and will happily regrow them. Although not every year.