If there were droplets of fertilizer/water left on the leaves, that could have caused those little burnt marks. Are they still appearing?
Two things to consider: First always water in the early morning so the leaves have a chance to dry off during the day. If you are using the MG as a foliar spray, rinse it off with the hose before the sun hits the leaves. Again do this in the morning ALWAYS! Second, water the ground under the plants, and try not to wet the leaves. If you're using a sprinkler, consider going to a soaker hose system or something that keeps the water low down, under the plants. Wet leaves are an invitation to fungus infection. I really like micro-irrigation, and it's pretty cheap and fun to install too.
I also agree that you must not expect perfection in plants, and not worry about every little spot or bug. As long as you have lots of healthy green leaf tissue, the plant is still making food for itself. If you do see a lot of aphids or other bugs, don't resort to a spray right away, try the hose-em-off method first. (but don't do it at night!!) Especially with edibles you must be so careful what you use.
I keep a spray bottle of soapy water for insects, one of baking soda and water for fungus prevention, and one of Bt in case of caterpillars. Those are the extent of my "sprays" that I'm willing to use on my edibles. I'm not a strict organic gardener either, but I do want to harvest healthy (to eat) veggies - that's the whole reason I grow my own.
