From the pictures there sure isn't anything major wrong with them. Likely some early blight but I sure wouldn't pull them! Assuming they were planted at the proper time it will soon be harvest/digging time anyway. That means all the tops, not just a few leaves, will all start dying back soon. If it worries you you can always use a mild fungicide on them. The light green color could simply be insufficient fertilizer feeding. Dave

Can't really tell from the pics as they aren't close enough to see the bull's eye pattern. There are 2 very different forms of "blight". Different causes and different symptoms. If there is nothing on the stems, just the leaves, then it could be Early Blight and that is the most likely. But if the stems are also affected and if the leaves develop large dark soft spots then it could be Late Blight. See link below for pictures to compare. In either case a regular spraying program of fungicide is needed. Were these planted in a different site than last year and were they fresh treated seed potatoes or ones you saved from last year? Unfortunately too many folks planted their own saved seed potatoes this year, ones that carried the late blight fungus from last year's epidemic, and we are now seeing a resurgence of last year's late blight problems. Dave Here is a link that might be useful: Potato Diseases

I had a similar experience -- only lost a couple of plants. I used grass clippings to mulch my potato bins. Heavy rains turned the clippings into a sodden mass that wouldn't dry out. My son took a lot of the mess out of the bins. The remaining plants look healthy and got mulched late (with weeds pulled from the garden). I have no idea what the potatoes will be like. I doubt I'm giving the potato bins a fair trial.

Yes, you are definitely being too hard on yourself. Buying certified seed only guarantees that the potatoes themselves aren't already contaminated with the fungal spores for various potato diseases. It is absolutely no guarantee that the plants grown from them won't get such a disease. The spores for these diseases are widespread in the environment -- whether a plant gets them or not depends more on its health, IMO, than on exposure, since they're all pretty much exposed most of the time from what I can tell. When you think about it, these spores must be everywhere -- each infected plant can generate millions to billions of spores, and these spores can travel for thousands of miles on the winds. You could have planted certified seed and still had the same results, especially in such a wet, cool, and humid year as we've had here in the midwest. I've had good crops from certified seed and good crops from grocery store potatoes, and bad crops from each as well, depending upon the year and the weather. The main disadvantage of using grocery store potatoes is, as you stated above, the sprout inhibitors used on them. I've planted ones before which looked all ready to sprout, and had them sit for months without growing. Once they get to the point they are well-sprouted, with about 1/2 inch or longer shoots, then they'll grow for sure, in my experience.