When should I apply a dormant oil spray to my fruit trees?
Dormant oil sprays are highly refined petroleum products that are mixed with water and applied to trees and shrubs to control aphids, spider mites, and scale. Dormant oils destroy pests by suffocating them. When applied properly, the thin film of oil plugs the spiracles or pores through which the mite or insect breathes.
Proper timing is critical when using dormant oil sprays. Dormant oils should be applied in late March or early April in Iowa before the trees show signs of breaking dormancy (before “bud break”.) Dormant oils applied in February or early March are not effective as insects are not actively respiring at this time and, therefore, not vulnerable to the oil’s suffocating effects. Dormant oil sprays should be applied as close to bud break as possible.