Usually caused by overly wet soil combined with overly cool air temps. When the leaves are having difficulty with transpiration they tend to swell and bow out like that trying to expand the leaf surface. You can'r control the air temps except with covers and when the overly wet soil is due to rain there is little you can do but it poses no real threat to the plants in the long run. But if the wet soil is due to over-watering - that you can correct.

I assume you plan to pull all the weeds ASAP? Easy to do when the ground is so wet.

Dave

I'm uncertain it's physiological leaf curl.

Looks more like herbicide damage. Any chance of that? Perhaps someone was trying to get rid of the weeds. Possible causative materials are anything with 2,4-D or triclopyr in it.

If you added manure to the soil, before or after planting, also could be herbicide-carryover in organic matter.

Review the images and text at http://smallfarms.oregonstate.edu/sfn/f09Herbicide -

Unfortunately, some of the links in the above article are broken.

If you suspect the latter, do the bioassay as described here - https://content.ces.ncsu.edu/conducting-a-bioassay-for-herbicide-residues

That's very detailed. But all you need do is plant pea or radish seeds in the same area. If the seedlings are distorted, you can safely plant grass crops this year (e.g.: corn) in the area but no broadleaf crops. Tomatoes are particularly sensitive.

Here's the original, well-illustrated site.

http://whatcom.wsu.edu/ag/aminopyralid/index.htm

Find Bioassay info via the menu at the left.

digdirt2 You are quite right! Dave I'm getting on to the weed issue. Thanks

Yeah other than 1 plant in the first pic (which shows no herbicide damage I can see) it is difficult to tell the potato plants from the weeds. ;-)

Dave