Unfortunately there is not effective treatment for wire worm..I know you probably dont want to hear that ..but there are steps you can take to help minimise the damage ...some of these I am sure you are already doing but thought I would mention them anyway ..
1 ..buy a resistant potato ...I sow piccasso .main which has some resistance and also crops a couple of weeks earlier than others which also means that 2. lift crops as early as you can to minimise damage ...I lift piccasso in late august ....
3 incourage insect eating birds with feeders etc ...
4. Turn the beds in autumn to expose the worms to predators ....
5. keep the beds regularly cultivated through spring & summer ..
Sorry I can offer not more advice ...hope you have better luck this year