WHOA........Check THIS out........Report from Texas A&M AgriLife Extension........
"Organically, only the planting of cereal rye (Elbon) in the fall to grow during the winter will decrease nematode populations. Excessive drying of the soil during July will also help. Another possible solution may be the solid planting of French (small blooms) marigolds for 3 months in areas heavily contaminated with nematodes. The French marigold, when grown on soil infested with nematodes, suppresses the population of these nematodes and reduces the numbers found in the roots of susceptible host plants. Three compounds of an a-terthienyl type, toxic to nematodes, have been identified in root exudates from these plants. Terthienyls are released from growing roots, even without their decay, but benefits require three to four months to become clear. There is some evidence that a-terthienyl is inhibitory to some plant-pathogenic fungi too. Marigolds also function as a trap crop since larvae which penetrate the roots do not develop beyond the second larval stage and do not lay eggs."