Vinegar that strong could harm the plants. Table strength vinegar is standardized at 5%, and while it isn't as good as 10% as an organic weedkiller, it can do it if you apply more often. I think applying half water half vinegar can harm the tender plants in the pot. If you choose vinegar, dilute it more.

Cornmeal is a good fungicide. If you have the corn gluten meal that they sell in garden centers, you could put a light sprinkling over the surface if you don't have any seeds still to sprout. It will block germination, it's only for a fungicide and fertilizer on established plants. If you don't have corn gluten meal, then put some cornmeal (if it is for a garden, a cup per gallon will work, but scale back according to your needs. Soak it for a few hours then strain the cornmeal and use the water on the soil. You might keep it in the fridge and water with that, it will fertilize and it will fight the fungus.

Another good fungicide is home-strength (3%) hydrogen peroxide. The stuff that costs $.50 a quart at the grocery store. Put it in a spray bottle and spray it over the plant and soil full strength. It won't harm the plant but it will take out the fungus. It's also a good treatment if you notice powdery mildew starting on plants in the garden. But I agree with Q about the diagnosis - you're probably overwatering. Let the plants wilt a little before watering. (A little - don't stress them out!)

SRS