Gosh darn, I hope you have tremendous success with perennial peanuts as a ground cover in that landscape.
I don't know if nematodes could be your problem, they ate my attempt at tomatoes in north Florida.
Let's see what pfaf. org has to say about
Nematodes
Ok,this sounds like it might do well as a companion plant in your climate:
Chop-Suey Greens "Possibly a good companion plant, protecting neighbouring plants from caterpillars etc. There is a report that secretions from the roots can be effective in controlling nematodes in the soil, but this has not been substantiated" Wow! It's used in the treatment of syphilis! Your renown as a witch doctor is assured!