Not guaranteed, but I have found that with a couple of collard plants in the growbed, the pierids lay their eggs exclusively on it and leave all my other brassicas alone. I'm just up the street from you, so I'll assume that cabbage loopers are what you're experiencing.
I'm on the other side of the planet and cabbage loopers still seem to love my bok choi (and other brassicas). I've been using a Bt (Bacillus Thuringiensis) based product. Mine is a brand called "Safer" and it seems to work well, but I know that other aquapons have used things like Dipel and Thuricide (they are all Bt based products with the same active ingredient) with good results.
Now, keep in mind any Bt product you use is going to require that the caterpillars ingest some of it in order for the bacteria to do them in. So you'll have to put up with a few more holes in your bok choi even after spraying with Bt...
Viad, i have read some about bt but was wondering about the run off into raft bed water?
Jeffery, i'll try any thing to maintain a pest free garden so collard in raft beds it is..
i'm in oceanside where are you?
I work in O'side and Cardiff (MiraCosta College), but my home is in San Juan Cap.
I'll be interested to see if the collard trick works for you as it seems to in my AP bed. I know that my pepper-growing friends will use an eggplant as an aphid attractor with the effect of keeping their beloved Capsicums aphid-free.
Trap plants are great. Currently I'm using watercress to keep my beloved capsicums aphid free (thanks again for the seeds Jeffery, they're all doing great). The cress is full of aphids, yet not a one on the peppers. Every now and then I'll lightly blast the cress with a pyrethrin mix (which unlike Bt, is not entirely fish safe so you can't go and use it indiscriminately).
Bt isn't a problem though for the fish. Neither is Spinosad A or D, nor is Beauveria bassiana harmful to fish. There are probably some other fish safe "bio" pesticides out there but those three (Bt, Spinosad and B. bassiana) are the ones that I've used without issues.
untreated, pest-loaded trap plant foliage can also be fed to chickens, who appreciate the extra yum.
Glad to hear the peppers are coming up, Vlad. I have a couple of kapija (one of each type) growing as late-starts and summer choi is in the AP bed now.