Something is cutting the leaves off my cucumber plants. What is it and how can I stop it?
There are several pests that could be doing this, such as slugs, cucumber beetles, and cutworms. Regardless of the pest, neem oil should help. Here is more information: https://www.gardeningknowhow.com/problems/pests/neem-oil-uses.htm
These articles should help pinpoint the culprit: https://www.gardeningknowhow.com/plant-problems/pests/facts-about-slugs-and-how-to-kill-garden-slugs.htm