This is the easiest and safest method of thwarting harmful insects, such as scale, aphids, spider mites, assorted beetles and larva. Dormant oil is a fine grade of machine oil, much like sewing machine oil. It mixes with water and is easily applied.
Insects are about to hatch from under the lumps of scaly material to form new colonies.
Thankfully, we are seeing fewer aspen trees in the urban landscape. They belong in the high country where they are not beset with scale, aphids and the aspen leaf diseases. The new shoots coming up need all the sun and air they can get. If the center of the clump is dead, it means that the clump needs to be divided. The easiest method is to water the plant the day before the job, dig all the way around it with a transplant spade and lift it out to a waiting tarp.