Potato leaf brown spots
We are growing some purple potatoes in our garden, and the plants are having serious brown spots on them. We did some research on the web, and the closest we came to was early blight. But the brown spots do not have concentric circles to them. here are pics: http://janetzhou.smugmug.com/Nature/Potato/i-bc4swH9/0/L/Potato-Leaf-L.jpg
Could it still be early blight, or is it some mineral deficiency, or other disease?