TreeBowl, you have come to the right place for help. Welcome to treebuzz.
As far as Insect and Disease Control, Hort Oil, will take care of adelgid, scale and many other soft body insects. You can start as soon as the Growing Degree Days do.
Then once Apples, cherries, Hawthornes, (and Anything else with Leaf Disease problems) buds start to enlarge. Start Spraying a good Fungicide, such as (Eagle, Propcanozal, Compass)
while you are doing these you can start with the Ferts (deep Root), can be done on light rain days, and any other time you are not spraying. also a good time for Systemic Insecticides such as, Merit for Harder to control things that come in to play later in the season (Lacebug, psyllid, BVW, List goes on)
late spring-early Summer time is PHC time (dont be a cover sprayer). Monitor landscapes and treat acordingly, start looking of abiotic problems, Girdling roots, heat and drought stress, over/under watering. Biotic problems such as aphids, Spider Mites, psyllid.. list goes on
Thats a start..... i will let another fellow tree buzzer fill in the rest