I'm into the 5th week of flower and there seem to be little yellow patches popping up on the sugar leaves on main colas. Should I be worried? Using 600w hps
No worries, it's completely normal. The last half of flower, the plants put everything into bud development, which means taking as many nutrients stored in non-reproductive parts of the plant and routing it all to the buds. I'd guess you only have 3-4 weeks to go till harvest. Good job.