I guess I could kind of see an argument for regulating what can be grown to some extent, like a government might want to have domestic food production in case of loss of access to imports, and might therefore have reason to make farmers grow food crops rather than some inedible crop that might have more value, but that still doesn’t explain regulating individual varieties of potato, particularly for this reason. If they clog machinery when harvested, won’t that by itself incentivize farmers not to grow them?