Elizabeth, you asked above about species. There are only four species of RKN's known. M. hapla is the so called Northern RKN and there are no tolerant varieties known, so we can eliminate that one ASAP. In all the years I've been posting about tomatoes I know of only ONE documented ID of hapla and that was in MI.
There are three species of Southern Root Knot Nemtodes, incogonita,javanica and arenaria. And at least 4 races are known.
What you have where you are is Southern Root Knot Nematodes and far and away the most common species is M. incognita, according to my tomato pathology monograph.
But they make no distinction between symptoms of the southern RKN's and while I've never researched the N tolerant gene source, it would appear that the tolerance is against all three of the species.
That being said, I don't see that there would be any great difference in using the Tagetes marigolds, the specific cultivars you mentioned above, if that's one route you're pursuing. However dense planting is the rule and letting them grow for the whole season and then turning them under does take the gardening area out of use for the whole season.
You can try that if you want to or any of the other suggestions folks have made such as the products that Suze mentioned that have worked well for her or continually adding more and more organic matter as Jack and others suggested to limit the spread and multiplication of them.
You're fighting the same fight that many before you and many now are fighting when it comes to RKN's so take solace in knowing you aren't alone if that helps just a bit.
