Marigold or amarillo contains a
chemical that is toxic to some pests in the soil, like
nematodes. Thus, it is good plant marigold together with
vegetable or in between farm crops. Nematodes are very tiny
parasites or worm in the soil, river, sea, rotting wood or
plants. They also thrive in other parts of the plant like the
roots, and in animals and insects.
Most nematodes are not harmful
but even helpful in the fertilizing the soil however, their
danger lies in that they feed on roots, stems or leaves of
plants they suck the nutrient.
From: Farmnews March-April