Mountain ash sawfly
Sawfly larvae vary from 1/16 to 5/8 of an inch long in Grand Rapids. There are generally two generations a year. So watch for this one again later this summer.
Reports of anthracnose on green ash were received at Perham in Otter Tail County in late May. Leaves appeared blackened and deformed with brown sunken spots. This fungal disease is particularly a problem in cool, wet springs but, can also be initiated if wet conditions follow hot humid conditions during leaf expansion. In severe cases, twigs die back and defoliation can occur however, new leaves will form again in mid-summer.
Destroying the fallen leaves usually is all that is necessary to maintain control. Watering trees in late morning may aid trees in leafing out again, especially during a droughty period. Late evening watering may fit with your work schedule but only favors the development of the disease.