Nematode populations requiring control usually will not be found in clay and clay-loam soils. In addition, successful fumigation of clay soils is very difficult to achieve. The main nematode problems in muck soils are root-knot, bulb and stem, or occasionally, root lesion. Bulb and stem nematode can be a problem on onions and other bulb crops. The best control is rotation to non-bulb crops for at least two years.
Lesion nematodes have a very broad host range and are difficult to control by rotation.
Rotation will control some nematode species. Northern root-knot nematode does not survive on grasses or grains, so a grass or grain crop can be used to reduce their numbers. Growing a non-bulb crop for at least two years is advised to control bulb and stem nematode. Beet-cyst nematodes only attack crucifers, beets and rhubarb. Do not grow these crops for a minimum of five years.