If infested plants manifest distinctive symptoms early in the growing season, they could be removed to prevent nematodes from infesting surrounding plants.
Daffodils infested with stem and bulb nematode (Ditylenchus dipsaci), for example, have distinctive symptoms on the leaves called spikkles consisting of raised bumps and yellowing.
This same nematode also results in distinctive symptoms on alfalfa, healthy on left consisting of shortening of the internodes.
An aware grower could removed infested plants from a field which would limit spread to other plants.