Vertical distribution of the plant-parasitic nematode, Meloidogyne chitwoodi, under field crops
Population dynamics of Meloidogyne chitwoodi were studied for 2 years in a commercial potato field and microplots. Annual second-stage juvenile (J2) densities peaked at harvest in mid-fall, declined through the winter, and were lowest in early summer. In the field and in one microplot study, population increase displayed trimodal patterns during the 1984 and 1985 seasons. Overwintering nematodes produced egg masses on roots by 600-800 degree-days base 5 C (DD) after planting. Second-generation and third-generation eggs hatched by 950-1,100 DD and 1,500-1,600 DD, respectively, and J2 densities rapidly increased in the soil. A fourth generation was observed at 2,150 DD in 1985 microplot studies. Tubers were initiated by 450-500 DD, but J2 were not observed in the tubers until after the second generation hatched at 988-1,166 DD. A second period of tuber invasion was observed when third generation J2 hatched. The regional variation in M. chitwoodi damage on potato may be explained by degree-day accumulation in different potato production regions of the western United States.