Looks like water stress on a battered plat. What does the rest of the plant look like? (show us, please)

I doubt the Jean's version... I have encountered with the same damage on my cucumbers , but still in search for an answer

I have a couple cuc leaves that look like that too......but only a couple, so I guess I won't worry about it....yet. Earlier in the season, I saw some white flies around the area. Don't know if they do that.

No, whiteflies don't do that.

I still vote for water stress on a battered plant. Perhaps it was windy?

Check out angular leaf spot. Very common with cukes, especially seed grown ones.

catherinet,

With my cucumbers it also started with just a few leaves here and there (which I removed immediately)... Now I'm loosing them plants

Looks like some type of fungal issue (probably old damage) to me. I would not stress about it.

I think this is a kind of element deficiency like magnesium and potassium and after tissue dying fungal saprophytes attack.