Michigan State University Extension
Ornamental Plants plus Version 2.0 - 00000468
01/01/98
The first noticeable symptom of fire blight is the browning of branch tips. The tips appear to be burned or scorched and the leaves droop but hang on the tree. Cankers form and the bacteria is washed farther down the branch by rain. The bacteria is spread from diseased to healthy twigs by bees. There is no satisfactory chemical control. Prune out blighted branch tips by cutting well beyond the diseased wood. High nitrogen fertilizer may increase tree susceptibility to fire blight.
Leaf blight caused by Fabraea thuemenii attacks most hawthorns but especially English hawthorn. The symptoms are small reddish brown spots on the leaves which may run together. Infected leaves drop in August and severely infected trees may be completely bare.
Cedar hawthorn rust causes orange or rust colored spots on the leaves leading to early defoliation. The fruits and twigs are also attacked. Juniper is an alternate host. Washington and cockspur hawthorn are resistant to rust diseases.
Scab causes leaf spotting and defoliation. The fruit have black raised spots on them.
Powdery mildew causes a white powdery growth on the leaves.