Any idea on what this is?

[sniffs]

All my lower cucumber leaves have this. It looks like some sort of trail or path that some creature traveled on but it's not going away. Thoughts?

https://goo.gl/photos/5PR9yQAeY2RrYB3F9

[digitS']

Leafminers?

LINK

Note that this pest is making trails inside the leaf.

Steve

[rainbowgardener]

Yes, indeed leaf miners. There are various types of them that attack different crops. All of them are insect larvae that chew their way around inside the tissue of the leaf.

As pests go, these are far from the worst, as long as you don't have a major infestation of them. The plant can lose a lot of leaf tissue that way before it really even notices. Just keep removing and destroying all the leaves with squiggles in them. Insecticides whether organic or poisons have no impact on the larvae, since the spray is on the outside of the leaves and the larvae are very protected inside. Besides removing squiggled leaves, you can put plastic down around your plants. When the larvae are full sized, they chew their way out of the leaf, drop down, burrow into the soil and pupate. If they can't reach the soil, the formation of a new generation is interrupted.

Lambs quarters and velvetleaf are good trap crops for them. The leaf miners will differentially attack these plants. You can just keep pulling squiggled leaves off these and your crops will mostly be left alone.

[ButterflyLady29]

You don't really have to remove the leaves. If you look close you can see the larvae inside the leaf. Just squish the larvae. For some reason that seems to prevent more eggs from being laid in that leaf. At least from what I've seen in my yard.