Question
Spraying zinc sulphate at dormant season on apple orchard provide some benefit or not.

Answer
Dear Vivek, I apologize for the delay in answering your question - computer trouble.  At any rate, the zinc sulfate probably wouldn't be very beneficial during the dormant season, because zinc sulfate is a fungicide.  Typically fungicidal sprays for agricultural purposes are used as foliar sprays (meaning on the leaves) because most of the fungus that a tree is susceptible to would be evident on the leaves.  Since at this time you have no leaves, it wouldn't help any of the typical fungus.  Should you have rot on the trunks it might help some, but that is better handled mostly through pruning.  If you have moss on the trunks, the zinc would probably help that situation.  I would definitely read all the directions on the packaging, but unless you are spraying for moss, it probably wouldn't do any good at this time.  Bear in mind that the zinc would help only for fungus, not insects, so any overwintering pests would need an insecticidal spray.  Again sorry for the delay, and I hope I addressed your concerns.  Good luck, Melissa