Nematodes, marigolds, and crop rotation

Marigolds as a cover crop: they are not only useful, but also beautiful and
attract butterflies and bees.

This summer, for several reasons, I skipped most of the summer crops and planted a cover crop of marigolds. I'd also planted a lot of marigolds around the tomatoes earlier in the season--about 3 marigolds for every tomato plant.

This is my experiment to see if I can reduce the root-knot nematode populations in my gardens.

First, as I've been preaching in my talks, just planting marigolds around the tomatoes does not prevent nematode damage. Here is the result...