Dense stands of marigolds are weeds in a vegetable garden because they compete with crops for essential nutrients and water. In many gardens and landscape beds, marigolds are also a common source of spider mites. Tropical Legumes Tropical legumes are often used as summer annual forages for grazing livestock and for improving soil fertility. Some have been shown to suppress damaging nematodes. Foliage of some tropical legumes incorporated into the soil as a green manure may also reduce populations of some root-knot nematodes.
Many tropical legumes are highly susceptible to attack by all common root-knot nematodes.
Forage crops that may be used for nematode suppression in vegetable gardens and row crop fields are discussed below. Castor bean cultivars evaluated for nematode suppression are listed in Table 2. Castor beans should be plowed under as a green manure before a seed crop is set. A single seed contains enough poison to kill humans, pets, and livestock. Seed availability is limited.