RE: Insecticides for apple trees?
Duckwhacker; what type of insect are you talking about? Is it in the fruit, in the tree or on the the tree? If it's a borer or diseased limbs pruning is often the best clean-up method. Deer don't mind a few worms in their apples. Unless you want some fruit for yourself it's usually best to spray as infrequently as possible, basically only spray when there's an outbreak. Otherwise you can upset the natural balance that takes place.
Like Early Riser says dormant oil is pretty essential to lower overwintering populations.
Dan O.