The yellowish appearance? Likely overwatering or moisture retention in the medium. (which looks like it could use some perlite, by the way) Either way, the soil is retaining water which can drown the roots. No need for spray if they're properly watered. Cannabis prefers a wet-dry cycle. Wet roots causes serious problems from stunting to root rot. Don't be a Root Rotter.

A good rule to follow when growing cannabis...is one plant per pot. You should either cull the little ones, or dig 'em out with a spoon or fork and transplant with care. Do it carefully enough, they might survive and thrive.