Some of these kinds of sprays will burn tender new growth, so — as a class — they are reckoned to be damaging if applied too late. This is not true of all, however. Modern light-weight oils can be applied for some purposes to growing foliage. When used as dormant spray, horticultural oil smothers insects coming out of hibernation. Its action is mechanical rather than toxic, so it needs to be applied while pests’ respiration is increasing — above about 40° F. The latest that such benefits are obtained is about 1/4-inch green, which can be a tolerably narrow window. If you miss it, don’t sweat it. It won’t do to apply in the rain or when rain threatens of course. It won’t do to apply when the weather is too cold, when it is too hot — above 80° F, when it is too dry, when it is too humid, or when it is too windy because the emulsion will either freeze, separate, or evaporate before killing insects and their eggs.