need help with yellow patches on new growths

I just recently topped my plant and a few weeks later one of the 2 main tops started producing yellow patches on its new growth. Before tis happened the lower leaves started curling with Brown edges. What should I do.


Here's a pic...

thats a standard deficiency or lockout of a particular nute, ill look for the page

Its a sulphur deficiency, easy fixed
http://www.cannaversity.com/cannaversity/article.php?id=057

well I shouldnt say easy I wouldnt have the first clue but.....