Spots on Leaves, what is this?

Hey guys,

I've already gotten this plant out of the garden and destroyed it. However, I still want to know what this was. I'm feeding organic so probably not nute burn. Also, there's no sign of this on my other four plants and no signs of bugs in the room or on the plant. Any input would be helpful, I was thinking some sort of blight or fungal infection? I noticed it this morning and visibly got worse during the day.