Several species of insects feed on it; common ones include hazel sawfly, winter moth, buff-tip moth, grey dagger moth. Look for caterpillars on the leaves, particularly between any leaves stuck together with webbing.

Note: it is a cultivar of Hazel (Corylus avellana), not of Filbert (Corylus maxima).

Resin

thank you i will give a good looking over when the sun starts to go down or early in the morn when im out in the garden. thanks for the note, I name all the trees i have planted i got filbert, wolly willow(corkscrew willow,and Jacob (pine i riped out of my brick planter in front of the house and stuck in a hole) so far not sure what next springs trees will be