ALDEVAUX

Yes, there are two dormant sprays : one for diseases (copper or sulphur)and one for insects and mites (horticultural oils) and they should be used at the recommended dose or dilution even when the trees are small or in pots.They could also be miixed together in the same sprayer.
Copper sulfate (sometimes called "fixed copper") is the best and most widely used dormant spray. As it is a powder that is mixed with water, it tends to settle out of solution, so you need to keep shaking the sprayer often.
Lime sulfur is as effective as copper and maybe easier to spray although it smells like rotten eggs, however, it is very irritating to the skin and eyes.
As I said, the dormant spray oil can be added to either material in the same spray mix.
Since both copper sulfate and lime sulfur can be irritating to the skin and eyes, it is very important to wear gloves, long sleeves, and goggles when you spray them -- especially if it's likely to drift with wind. The dormant oil is very low in toxicity.
If it rains on the tree within 24 hours of spraying you should spray again because the spray did not have time to stick well enough. It might be better to protect the tree from rain until the spray is well dried.
It does not matter if the spray falls on the soil but wait at least 2 days after application before wetting any part of the tree that was sprayed.