To be most effective, crops that are poor hosts or nonhosts of the target nematodes should be included in the rotation sequence. Root-knot and lesion nematodes have such a wide host range that a practical rotation plan to reduce these nematode populations for vegetable crops cannot be recommended at the present time. Cover crops . Some plants commonly used as cover crops are naturally suppressive to certain nematode species, but no single crop is effective against all nematodes. The cover crop plant may be a nonhost and, therefore the nematodes starve, thus reducing their populations as with fallow.
Nematodes invade the roots of certain other cover crop plants, but they fail to reproduce.
Soil amendments and green manures . In general, the incorporation of large amounts of organic matter into the soil reduces populations of plant-feeding nematodes. The decomposition products of some plants kill nematodes. These include butyric acid, which is released during the decomposition of rye and timothy, and isothiocyanates, released during the decomposition of rapeseed and other plants in the genus Brassica. Maximum benefit of these natural nematicides is obtained when the plant material is incorporated into the soil as green manure.