Mild to medium (Mg) deficiency, flush well on the last flush apply 1 teaspoon of Calmag or Epsom Salts, of more immediate concern is the extreme to serious nute burn of the distant top right plant see pic! ..to my blog: http://forum.grasscity.com/blog/1093/entry-9829-flush-baby-flush/
I don't know if cannabis is vulnerable to powdery mildew, but that's exactly what it looks like on a squash plant. If it's not nutrients you can try a simple mildew recipe - 1 part whole milk - 1 part dish soap - 8 parts water, spray lightly. It's harmless in the event that it is a simple nutrient problem.
PM or powdery mildew a mold is best handled with Neem Oil, to test wet your thimb and wip it of, if it wipes off is white-ish or grey you can guess its Pm, if it don't wipe off see it as nute burn
i would say neem oil as well. what do the undersides of the leaves look like? get a magnifier and see if you might have some tiny sucking insects on the plant. j