I had something plaguing my California Wonder Red Bell Pepper Plants, I wasnt sure if it was a fungus or a pest (I was leaning more toward pest after I found a small beetle of some sort residing under a leaf). Luckily there is this great organic product called Neem Oil. Neem Oil will treat for bugs and for fungus. It should be applied about once a week to once every two weeks however it is an oil so don’t apply it when the plant is getting direct sun, or it will get sun scorched. Applying in the evening is best. My bell peppers are doing much better since their treatment last week , their leaves have really gotten much larger and I’m not seeing any damage to the new growth. I also use Diatemacious earth but find it not as effective because when the elements (water or wind) wash it off the plant it needs to be reapplied, also Diatemacious Earth will kill the bees and other pollinators and we don’t want to do that.