Tree leaf gall
What causes gall (nipple like protrusions) on back of hackberry leaves? Is it preventable? Tree is approx 10' tall & this is second summer in our yard.
Stearns County Minnesota
Nipple galls are caused by the feeding of a small insect called a psyllid:
Nipple galls do not harm the tree, so no control is necessary. You can reduce the number of psyllids by raking and burning the leaves in the fall.