Just as in many other situations, pesticides are not the solution to a leaf miner problem. The miners are in between the layers of the leaves protected from any pesticides. I think this was pointed out to you in your previous post about this a week ago, right? So if you haven't actively intervened in any way since those original posts then there is little you can do now except cross your fingers and hope.

Have you been removing all the eggs pictured on the spinach leaves you posted photos of or removing the obviously infested leaves from either crop? Look at the beet pics - see the unaffected new growth? When you just leave all those damaged and infested leaves on the plants the infestation just spreads as the larvae on the old leaves emerge and spread to the new leaves.

Dave