Many states have license requirements for pesticide applications. You should check were you live, try the dept. of ag. or conservation dept. There might be a study guide or training course available. Sometimes these are run through extension offices. There is a best management practices guide (ISA) and ANSI standard for the fertilization of trees and shrubs.
The most important thing is to Always Read The Label. It is a violation of federal law to use a product in a manner that is inconsistent with it's label. Pay attention to the PPE requirements some of the chemicals are very nasty and can cause you to lose an eye or worse.
"Does anyone know if there is a course on spraying and fert where i could learn."
Other than the obvious liscensing requirements what do you want to learn? There are a number of books out on pest and disease control and a couple on fertilizing. I think an excellent starting point is to learn some ecology and soil science. Look into soil food web websites and books to get a look at an intergrated approach to improving soils that may help plant health.
It is easy to spray and fert but are you dealing with the problem?. Soil fert is a particular problem, if you kill the life of the soil all the additives will never make for a healthy tree.