Can you please send some pictures of the underside of the leaves so I can see if there are any eggs, webbing or pests on the plants? With that much devastation, it seems like there should be a culprit nearby.

Attached are three photos of underside of the leaves

I think it is very possible that you have earwigs or Japanese beetles, both of which can be tricky to see and find during the day. Here is some information on both of these:

https://extension.colostate.edu/topic-areas/insects/european-earwigs-5-533/

https://extension.colostate.edu/topic-areas/insects/japanese-beetle-5-601/

I think it is more likely earwigs and you can try to set out some traps to see if that helps. Fill a shallow plastic container with 1/2" vegetable oil and push into the soil a bit, so the earwigs can easily crawl into the container. The oil prevents them from getting out of the container. 

I hope that helps and good luck! 

I know there are earwigs in the garden.  I noticed a bunch around the stem of some bok choy. Do earwigs eat the leaves of arugula and brassicas  like kale and mustard greens as well as beans?

Hi,

Yes, they certainly can. They like moist and decaying plant matter, so if your mulch is consistently moist you may want to let it dry out once or twice a week after you trap them and eradicate most of them. Here is an informational for youhttp://csuhort.blogspot.com/2014/08/earwigs-case-of-ewhttp://www.html

Another pest that eats kale and mustard greens are aphids: https://planttalk.colostate.edu/topics/insects-diseases/1402-aphids/

Here is a handy list that may address the pest(s) targeting your brassica vegetables: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2617&context=extension_curall

Hope this is helpful!

Kind regards~

Thanks!

I tried the veg oil trap  - worked pretty well!  Two traps and got 20 or so earwigs, and a ton of little black bugs, about the size of a pinhead.  I didn't think aphid to begin with, but read the article on aphids at the link you sent, and see that they can be grey and brown.  These look black to me, and sort of iridescent black.  I've attached a photo of them in the trap.  Are these eating the plants and if so, anything other than the oil traps that can deal with them - hopefully not a pesticide? 

Hi,
 It looks as though you have Flea Beetles, which are quite common. Here is some information about them:

https://extension.colostate.edu/topic-areas/insects/flea-beetles-5-592/

Hope this helps, but please do let us know if we can be of any further assistance.

Best regards ~ Boulder County Master Gardeners