There is no need to foliar spray any plant unless its a quick fix for a deficiency or you are fighting bugs. I don't even spray cuttings when cloning. Just adding a lot of unneeded moisture to the air and if the plants have healthy roots they can take up more nutrients than they can use thru the roots. That how they get nute burn most times so why add to the load? Also increases the odds that you'll end up with a fungal disease or the dreaded powdery mildew.
And to the guy who claims that fading leaves are stealing nutrients and energy from the plant it's the other way around. They are fading because the plant is stealing mobile nutrients from them as it should be doing as it nears the end of it's life. If everything is still dark green to the bottom at chopping time it just means your plants have too much food in them and you'll be smoking it later. If the yellowing leaves are going all dry and crispy then it's probably toxic salts buildup that's killing them as natural yellowing in later flower the leaves are soft and supple before they dry up and fall off the plant.