This damages looks mechanical, i.e. like they took a battering.  You'll notice that the newer leaves look fine.  We don't think this is insect related.  You should see insects if they are there.  About the only insect possibly active now on cucumber would be cucumber beetles and you should be able to see them: http://extension.umd.edu/hgic/cucumber-beetles-spotted-or-striped-vegetables 

 Give the plants time to grow and put out new growth. If they are too damaged already, and don't take off soon, you may want to replant with new transplants.



ECN

Thank you so much! 

You're welcome!