Foliar feeding isn't scary! In fact, it has application in treating observed deficiencies WHILE you are trying to figure out how you got them, by bypassing the roots.
I like to feed my plants with a weak solution of the 'GH Micro' from the GH 3-part. I mix it up at about a tablespoon in a quart spray bottle, with a drop of dish soap to make it 'stick' (surfactant), and mist lightly. That buys you more time to fix the source of the problem.