Leaves have black spots of insect excrement, especially on lower surface.
Insecticides are warranted if the tree is small or under stress. Damage to large, vigorously growing trees is often aesthetic. Carbaryl, cyfluthrin, imidacloprid and malathion are insecticdes labeled for control of this pest. Quince fruit affected by quince rust. Rusts have been very serious on hawthorn trees in Missouri in recent years.