Thank you for your question about preventing scab on your potatoes. Unfortunately, continuing to grow your potatoes in the same location year-after-year can cause the buildup of scab in your soil. It is recommended that you rotate your potatoes:

“Avoid growing potatoes in the same section of the garden year after year, since this causes a buildup of soil-borne diseases including verticillium wilt and scab. Tomatoes, strawberries, and eggplant also are susceptible to wilt and should not precede or follow potatoes in the cropping sequence.

Common potato scab first is expressed as minute reddish-brown spots around breathing pores (lenticels) in small tubers. The lesions become larger and darker to form circular scabbed areas that may be isolated or coalesced to form large corky masses. While scab does not affect food quality, severely affected tubers are unmarketable. Most russet varieties are resistant to scab.”
Source: Grow your own potatoes | OSU Extension Service (oregonstate.edu)

If you need additional information, I recommend you call the Deschutes County OSU Extension office in Redmond at<personal data hidden>. Ask to speak with Amy Jo Detweiler (oregonstate.edu), a member of the Horticulture Staff. Amy Jo welcomes your home garden questions and is a great resource.