Another pic of yellow leaves...

That leaf in the second photo: I've never seen anything like that on a cucumber. Roundup damage on tomatoes bleaches out the green, but I don't know how Roundup (or other herbicide) would affect cucumber leaves.

I can't see enough of the white stuff on the stem to guess what that is.

If you don't get more definite answers here, post on the Vegetable Gardening forum.

Thanks. I did post in veggie growing forum too, with no hits. If by roundup you mean weed killer, it hasn't been exposed to any. Whatever it may be, it doesn't seem to be progressing rapidly.

I haven't seen that yellowing pattern either (though I'm also a beginner pretty much). I would make sure to water consistently and keep an eye on it - maybe just transplant shock of some kind? Hope it clears up!

There are many weedkillers besides Roundup (glyphosate), but Roundup exposure does result in pale leaf areas (on tomatoes, anyway -- but iirc, leaves affected by Roundup are also stunted). Other herbicides have different effects (twisted, malformed leaves, for instance).

But what most folks don't know is that sprayed herbicides can blow on the wind for long distances. Might not even be someone in your neighborhood!