Eventually, the leaf falls off. This accounts for the defoliation seen in spring. The leaves appear green when they fall leaving a carpet of green leaves on the ground. The tree responds by producing a 2nd growth of leaves. During the long winter and early spring the roots die because of the shortage of carbohydrates reserves.
Crown die back occurs to compensate for the loss of feeder roots.
This explains why so many ash trees in the metro area are showing symptoms of die back and decline especially ash trees already weakened by other stress factors. Depending on the weather a 2nd application may be needed later on in late spring. If it is dry, the 2nd application will not be necessary. Suggested products are Daconil or other chlorotholnil products. Fire blight causes disfigurement of the branches and may cause death.