Seasonal Fluctuations of Globodera tabacum solanacearum as Estimated by Two Soil Extraction Techniques

Two soil extraction methods were compared to determine their efficiency in recovering cysts and juveniles of a tobacco cyst nematode, Globodera tabacum solanacearum. The methods were equally efficient when extracting nematodes from soil samples seeded in the laboratory; however, there was a significant extraction method x month interaction when the methods were used to estimate field soil populations over 2 years. The centrifugal sugar flotation method recovered greater numbers of cysts when densities were near 400 cysts/100 cm(3) soil and greater numbers of juveniles in all samples. The sugar flotation method recovered greater numbers of cysts during months when densities were less than 400 cysts/100 cm(3) soil. Numbers of cysts and juveniles were lowest in June and July following land tillage in May. A soil freeze in January 1982 may have been responsible for unusually high numbers of recovered cysts in February and March 1982, a pattern that did not occur in 1983.