Dude you sure better look on the underside of that leaf in the pic!!!!! That looks just like the mite damage that my gurls suffered! Got a magnifying glass?Check for the crawling critters!The damaged parts on my leaf was white to brown to black! They even started to yellow some as well!I know for a fact my problem was not nute burn! It was FREAKIN' MITES! I hope it is just a nute burn!

Ga Grown!