Just planted my cucumber plants, all 2 of them, and they're both looking the exact same. Been searching for a answer but couldn't find one that matches my photo.
What zone are you in? Did you harden them off before transplanting them? It is still very cold in many parts of the country for cukes.
Also, they tend to do better direct seeded, they can be transplanted but in my experience the direct seeded ones do better.
The damage to me looks like it could be environmental... sunburn, windburn, excessive cold... this would be caused by setting them out without hardening them off first, or setting them out too early if you are not in warmer zone.
Im in zone 7, central Alabama
What have your night time temps been averaging? I'm further north but also zone 7 and I won't get my cukes going for at least a few weeks. You could give them some protection at night by covering them with an empty pot before the sun goes down and then removing it again in the morning so they don't cook during the day.
I would check with your local agricultural extension for the best dates to sow them in your area and consider direct sowing some seeds. Odds are, they will catch up and surpass your transplants.
Well unless your weather there has been much better than for other folks in that area it is too early for cukes. That looks like a plant that wasn't hardened off and either got wind burned and possibly now has nitrogen burn on the leaf edges.
It might recover and if not there is still plenty of time to direct seed. As howel said they don't like being transplanted anyway. It gains you nothing and often kills the plant.
What is hardening?
Either sunburn or due to cold.
Cucumbers tend to get yellow like that in cold temperature but as it warms up new growth should be fine.