Leaf fertilizing by spray - experiences

[tedburn]

I have some citrus which after winter show deficits by their yellowish leave color, I suppose Iron and mangan.
With soil fertilizer I don' t get it totally fixed, especialy the one year old leaves.
Who made good experiences with leaf fertilizing by spraying and can tell me some rules, as at which time to spray, can I also affect older leaves, how often has to be sprayed, how long does it take to see success ?
Thanks for your information, regards Frank