Hi there - I'm growing cukes in Earthboxes with Sunshine Mix this year (first time trying them in these boxes).

They're growing vigorously, but I'm seeing pitting and yellowing (see pics). The bottom older leaves are really looking ragged with holes. The mid-upper leaves are starting to fade.

Is it Spider Mites? Cucumber spot? Too much fertilizer?

Any help appreciated, thanks!

(bottom leaf)

(about midway up the plant)