Keeled slugs could be the problem; infestation made easier as the tubers appear to have scab. If this is the case then I wonder whether the seaweed has made the soil a little on the alkaline side. As far as the slugs are concerned, lets hope for colder winter and a few hard frosts.

I'd go for slug damage or eelworm damage.

For slug damage I've tried putting a few pellets in the planting holes but its hard to know how much difference it made. If you dig all the potatoes as soon as they are ready rather than leaving them in the ground this can cut down the damage too.

Thank you Jommyeone, Seaburngirk & Steragram.
I did not find any snails,or worms in the potatoes and very little earth worms.
I did use a fair bit of non washed seaweed, I will cut that down next season. I also used slug pellets mixed through the soil. If you have any more advice I would be most grateful.

John

I think it would be slugs all the same. You were just lucky they weren't still there...can't think of anything else that would help - these things happen...but do dig them up rather than leaving them in the ground if this is a regular problem.

Thank you Steragram. I have removed all the potatoes from the plot. I did check carefully to see was their any sign of the slugs and did not find one. A fellow gardener uses lime in his trench before he plants his seeds potatoes and had no problem with his. What would you think ?

You don't always see them - they are not the usual big ones but very small black or dark brown ones

I was wondering about lime but Jimmytheone was suggesting that the seaweed might have made the soil too alkaline, and lime would make it more so. Why not try it on some and not others and compare results? You could send a PM to Hank - he grows heaps of veg.