I recommend applying a horticultural dormant oil i n late winter or early spring. Applying this dormant-season spray protects apple trees, pear trees, pie cherry trees, and grape vines from scale, mealy bugs, aphids, mites, and pear-psylla.ormant-season sprays are a great preventative and growing-season sprays help provide control as needed. After the very unusual spring experienced in most parts of the country, our best offense to a better fruit harvest this year is a well-executed spray schedule.