Thank you for your question. Although the photo isn’t clear, it would appear that your plant has anthracnose, that you can read about here: https://www.extension.umn.edu/garden/diagnose/plant/vegetable/cucumber/leavesspots.html In order to get a definitive diagnosis, and some help with control, I suggest you visit the diagnostic center identified here: http://ccenassau.org Take more photos and some browning leaves, since they may wish to use a microscope. Good luck!