|What causes the leaves to curl up early in the Spring when the leaves are just coming out?|
|I suspect you are seeing ash leaf curl caused by aphids. Aphids suck the juices from the leaves of the plant and usually deposit a sticky substance called honeydew. Their feeding results in twisted, curled leaves. If you uncurl the disfigured leaves, you will see aphids as well as white, waxy material that the aphids produce.
Ash leaf curl aphids also produce large amounts of honeydew which covers leaves, branches, and other nearby objects. Honeydew is a waste product that aphids produce while they are feeding.
Despite the appearance of the misshapened leaves, these woolly aphids do little actual harm to ash. Ash leaf curl aphids are regulated by natural enemies and should not be common on a particular tree more for more than a year or two.
An application of a systemic insecticide, such as acephate (Orthene) or dimethoate (Cygon) would effectively manage these woolly aphids. Insecticides, however, do not affect leaves already disfigured; they remain curled for the rest of the season. Be careful not to over apply insecticides to avoid negatively affecting natural enemies.