Keep trees healthy with regular fertilizer applications. Scales of several types infest prunus. Dormant oil is used to control overwintering stages. Sevin, Orthene or malathion controls crawlers when present. Identify the scale for proper timing of crawlers.
Spider mites cause yellowing or stippling but are very difficult to see.
Tent caterpillars make large webbed nests in trees then eat the foliage. One defoliation may not be serious and small nests can be pruned out and destroyed. Use Orthene, malathion, or Sevin when webs are first seen and insects are still small. Bacillus thuringiensis may also be used. Visuals associated with this text.