Why are my potatoes dying?

My early potatoes (sante) have gradually gone yellow then brown then dead, starting at the end of the row which is closer to the lawn. The other variety of potatoes and so far fine.
I can't see anything on the plants and no insect damage. It has been dry but I have been watering them as much as I can.
Any ideas what it could be so I can save the others please?

 

I think they're probably just ready for eating Louise. Enjoy.

 

I think they are ready to harvest.

 

It could be caused by an ants' nest down amongst the roots. They take out several of my plants every year.

 

Louise, lift a plant or two and see what`s underneath them.

 

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Hi Louise,
Sante is a main crop potato.

Mine are planted in my allotment, have had no water since planting except a couple of showers, the foilage is normal colour for them, maybe not as tall as normal.

But I have no idea what could be your problem.

Dig up one root and have a look see!

Cheers!

 

Thanks everyone.
I dug a couple up and have left the others. I didn't realise they were main crop ( they were sold as earlies!)
There seemed to be a mass of loose stringy roots that didn't belong to the potatoes and they didn't seem to be attached to anything,but I do have some trees not too far away and suffer a bit with horsetail weed. There was some small damage to some of the spuds and the soil was a bit dry too, I have watered the rest and given them some liquid fertiliser.

 

So no sign of ants amongst the roots?

This is what my spuds look like when they nest under the plant (first of the year):



And to make things worse they attack me when I try and salvage what's underneath.

 

My entire potato garden died before it even got a chance to flower. The stems got yellow at the base and they all just leaned over and died. I have 2 varieties of spuds that all are dead in my garden. I don't see any evidence of ant hills in the general area.