Looks like leaf burn to me. Did they get exposed to more intense or accidental direct light (from opening the cold frame on a warm day, etc.)?

I'd also check carefully for pests, but pic #2 looks like burn to me.

We've had a lot of days with above normal temps ... 70s/80s ... so I open the cold frame completely then, removing the tops. On days in the 50s/60s I just vent. Have always done the same, but never had this problem.

Thanks for your help.

Was it windy on the days you opened up the top? Looks like burn to me too. They should be fine.

Yes, they will recover. I might throw a very light shade cloth over them on days when you remove the cover. That will provide some protection from both wind and intense sun.

Again, thanks to both of you! Your information was confirmed by a local Ag Center agent.