Cause Meloidogyne spp. are soilborne nematodes with a wide host range. Many weeds such as dandelion and nightshade are alternate hosts. Most root-knot nematodes on alfalfa in the Pacific Northwest are northern root-knot nematode (M. hapla). However, some fields are infested with the alfalfa race of Columbia root-knot nematode (M. chitwoodi race 2), which does not produce galls as large as M. hapla does. Occasionally both species infest a field.
Symptoms Small distinct galls on roots. In some cases, the disease may produce a hairy-root condition near the crown. Plant vigor is reduced, and roots may be more susceptible to attack by root-rotting fungi.
Sampling Before planting, take soil samples with sufficient lead time to implement management procedures if necessary. Fall sampling for crops to be planted the following spring is an excellent strategy. In established plantings, samples can be taken any time during the growing season, but numbers will be highest during late summer. When sending samples for diagnosis, it is best to include roots as well as soil.
Cultural control
- No presently recommended variety is resistant, but a few resistant varieties such as Archer by Agri-Pro and University of Idaho have been developed. Relative resistance ratings of varieties are provided by the National Alfalfa and Forage Alliance (alfalfa.org).
- Good weed control practices will reduce population levels of nematodes.
Chemical control Experiments with nematicides indicate it is possible to improve the stand and increase yield in some infested fields with preplant soil fumigation. However, it has not been economically practical.