u/Familiar-Bike-3870

I have over 200 flats of Vinca Flowers in several locations that are dying and i cant figure out why. They first start to wilt a little but soil is moist. Not long after they start to wilt they look like the pictures. We had a bunch of rain so I turned the irrigation systems off. I sprayed them with a fungicide, 3336. Doesn't seem to have helped. I just put a granular fungicide on them since we have rain coming. They are all on drip irrigation so it's hard to get any chemicals to them. They as all in full sun. Is this some type of Fungus? Is it something else? Is it treatable? If treatable then how? Any help with identifying this problem would be a great help.