Squash Leaf Problem

[GoDawgs]

Yesterday while I was watering I found this fungal or whatever problem on one of the two Butterbush plants. They're young, 18 days out from germination with each having two 5" wide leaves, both of which are funked up. The several younger leaves are clean... so far.

Front of leaf:



Back of leaf:



Leaf petioles were clean. There seems to be a whitening along the edges of the main veins. I checked photos online last night and it doesn't seem to be septoria or phytopthora. It's almost like a severe angular leaf spot but it came on this plant a lot faster than angular leaf spot hits my cukes.

Got an e-mail w/photos sent to my extension guy but was just wondering if anyone has seen this before.