Root-Knot Nematode of Alfalfa
There are five species of root-knot nematodes (RKN) important for alfalfa production including northern (Meloidogyne hapla), southern (M. incognita), Columbian (M. chitwoodi), Javanese (M. javanica), and peanut (M. arenaria). Northern RKN causes the greatest losses in alfalfa. Aboveground symptoms are nondescript and appear in patches or throughout a field as yellow, stunted plants. Plant dieback may be observed. Root proliferation occurs belowground, along with shallow root systems with short taproots. Root galls are diagnostic for RKN. Rhizobium nodules can be removed easily, while RKN galls develop within the root and cannot be removed. Root-knot nematodes can increase the severity of Fusarium wilt, bacterial wilt, Phytophthora root rot, and alfalfa stem nematode through the formation of disease complexes.
Northern root-knot nematode on alfalfa.
Craig Grau
Second stage juvenile nematodes infect alfalfa roots and establish feeding sites that enlarge into root galls. Several generations can occur annually. Root-knot nematodes are often more problematic in fields with sandy soils.
Root-knot nematodes are best managed by planting resistant cultivars, especially in sandy soils.
Prepared and reviewed by the Alfalfa Pest Management Working Group.
Northern root-knot nematode on alfalfa.
Gallery images courtesy Craig Grau.
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