Mine look like that too and I chalk it up to late season old age combined with insect damage, possibly spotted or striped cucumber beetles with help from some squash and stink bugs. By mid Aug my cuke plants are exhausted, so I plant more by late May to prolong the harvest......prolong it a little bit as these pests love new digs.

I came here to get answers as well, because mine look the same! Was wondering if it's a fungus that can be treated before all my cucumber plants die. Planting earlier in Michigan isn't an option because of late frosts.

I did have some cucumber beetles and squash bugs but was very aggressive at eliminating them. It was very rare to find them on cucumbers.

Thanks! I do get cracking and stuff getting at them (not typically an issue for me) so I understand picking early. I thought nothing gets sweeter when picked - it may ripen but not get sweeter.

Last post was supposed to be elsewhere sorry!