Fungus amungus

do not water overhead. Full sun. mulch to avoid dirt splashing on leaves. In continuously rainy weather, give up. with chard, I have some experience that suggests (it could be myth) that it resists fungus better when the pH is of its liking (about 7). OTOH, I never had fungus on spinach, which is 6 feet away from chard, so you might be in a worse situation than I am. i am sure that there is also a vinegary or soapy concoction that could help.

Try a milk spray of 1 part milk to 9 parts water, spray 3 times 5 - 7 days apart.

bordeaux dust most nurseries carry it in their "organic" or "natural" section. it's the bestest solution against mold, fungi (funguy?), and powdery mildew.