neem oil is a little better than general dormant oil.
It's main use is to smother immature insects and insect eggs, basically choking thei air supply off. The neem does have some properties that can help with bacteria and fungus to an extent. I only spray before buds start waking up. Some swell is ok. Done properly you see a light coating of oil on the tree.
I have never sprayed that on a tree with leaves.
This year I did spray with copper twice before leaf out. mainly for my peaches for peach leaf curl. I also sprayed trees with cedar apple rust issues and a bartlet pear tree that gets fireblight. I used bonide copper spray. The nurse branches on droptine and pristine dont have a spot of rust on them. I am converting those trees to kerr and trailman. Golden delicious is staying that way and looks good too. One peach tree is curl free so far, the other has it in some spots, but looksa ton better than last year with no treatment.
I mainly use malathion for insects. Works great, not too nasty of a chemical either. No residual effects. Usually spary early to mid may, then late may to early june, and maybe one late june for japanese beetles.
Only sprayed once this year so far 2 weeks ago. Looking pretty good so far. Think I hit a sweet spot in critter development.
You able to reach the top of the trees. Sometimes the mid level brnaches get soaked too much trying to get the top of the tree.
I use a leaf blower with a tank. However, I have a 4ft extension wank for my pump sprayer. Can reach 10ft tall younger trees easily with it.
Malathion can be bought at bix outdoor stores like lowes and home depot. Spectracide one seems to work OK for me. Will likely buy a more larger bottle next time.