The way the anti-nematode marigolds work is one has to plant the whole field with the right type of marigolds for 2 years running to reduce the nematode population. That means no tomatoes for those 2 years on that patch of land.
The nematodes go into the marigolds and die. One also has to keep the weeds away for the 2 years.
I have never had to deal with that pest, but I was taught about them extensively in college. It may be that things have changed, so take my advice with a grain…
