I've done the same thing! Purchasing certified seed potatoes is not a deal breaker! Rotating your crops is crucial. I get my stock from Potato Gardens in Colorado. I have to limit myself purchasing potatoes otherwise I end up with a big bill and those potatoes have to be used immediately. A few years ago my main crop was Potatoes!! Not much room for anything else! I got carried away! I am working on a potato cellar with the correct humidity and temperatures that stay stable...and extend the usable life of my potato crops (and garlic, onions, rutabagas, carrots, fennel bulbs...).
Potatoes and tomatoes are horrible with disease (to include peppers and eggplant). Once you have blight it is a done deal, death and destruction and all of your work, fertilizer, watering...was just wasted. Makes those seed potato expenditures look really CHEAP.
There is no fungicide I would use on my plants my edibles to control this BLIGHT stuff. There is no control. There are ways to reduce exposure to soil containing spores that splash up on the plant and then kill it...lots of work. Pots really work well. Just One spore infects your plants and they are done. And so is that bed for use by the family Solanaceae for a minimum of 2 years! You can see how pots and sterilized potting soil would enlarge your garden and prevent heartache!
I use pots and potting soil for my tomatoes and peppers to enlarge my garden and heck potting soil is sterilized. Potatoes need very acidic soil so creating acidic beds to grow potatoes, blueberries really reduces the amount of space for productive growth of other vegies not liking that low of a pH. Potting soil is easy to get to the proper pH as well. I'll go find my catalog and send you this potato site or you can look them up. Extremely helpful small ma and pa and kids...family business. I've had many discussions with the owners!
Yes, always always always get certified seed potatoes. If you don't you will effectively ruin a bed with disease and that will take longer than a few years to eradicate and be able to plant that family in that bed again. Certified plants, starts, non-gmo seed are worth their weight in gold!
Here they are. I've had top notch service from this company. They'll send your order to arrive on whatever date you want. Excellent product, I've not seen one bit of decay and my taters arrived ON THE DAY I asked! Also, the owner's son or nephew...is a soil expert. A real soil expert and they have a product to help reduce the pH of the soil as well as feed soil organisms. A little boost to add to a correct maintenance program. And you can call these potato specialized growers to ask questions! This expanded my 'potato harvest' world and all I can say is the investment is no big deal and the success really is a big deal.