These are galls that form on the leaves in response to the feeding activity of an aphid-like insect called a pecan leaf phylloxera.
If there is a bad infestation where many galls form on many of the leaves, the tree may experience early leaf drop and the tree may become stressed. This is a worse case scenario.
Often control measures are not needed. If control is necessary, Bonide Eight can be sprayed in early spring just as the leaves begin to grow and before the galls form. Once the insects are surrounded by the galls, they are protected from chemical sprays.
Bonide All Seasons Oil can be sprayed on the trunks and branches in the late winter to smother the eggs that are laid on the bark.
Read more about galls on our Viette's Views blog