Down here on the Gulf Coast root knot nematodes can destroy gardens. Commonly people bring them home on tomato plants and once in the garden they are near impossible to eradicate.
I’ve been reading ‘Silent Spring’ in bits and pieces and tonight’s reading mentioned the use of marigolds as a treatment for root knot nematodes. After a bit of digging through old texts and online I discovered marigolds are still commonly used as a treatment for infected soils.
In ‘Silent Spring’ Rachael discusses success had planting marigolds among roses in some infected soil. Down here it’s your vegetable garden that is likely to be the problem.
The marigolds release alpha-terthienyl through the roots. The alpha-terthienyl is extremely toxic to nematodes, many insects and viruses. It works by preventing the hatching of the nematode eggs.
In addition, nematodes can not feed on marigold hosts, so you are also denying the nematodes food.
While you can always plant nematode resistant plants ( check for the N on the plant label ) Marigolds might be a nicer option.
Not all marigolds will prevent and harm root knot nematodes, do a bit of research first.
Varieties recommended for control of southern root knot nematode include: Tagetes patula, T. erecta, T. minuta.
Marigolds ( Tagetes spp. ) for Nematode Management