SEASONAL POPULATION DENSITIES OF HOPLOLAIMUS COLUMBUS AND THEIR IMPACT ON SOYBEAN YIELD

During the 1991 and 1992 soybean growing seasons an experiment was conducted near Blackville, South Carolina to study the seasonal population fluctuations of Hoplolaimus columbus in soil and roots and their relationship to seed yield of soybean. The soybean 'Braxton', susceptible and intolerant to H. columbus, was planted in a field naturally infested with H. columbus on 17 May 1991 and 19 May 1992. Nematodes were recovered from soil samples at planting and from soil and root samples at various times during the soybean growing season and at harvest. Nematode/g dry weight of root was highest on early sample dates. Nematode numbers from soil increased over the growing season, with highest numbers from 16- to 20-weeks after planting. Hoplolaimus columbus juvenile recovery from soil increased through the growing season and was generally higher than adult recovery. Recovery of H. columbus adults from soil or roots remained fairly constant throughout the growing season. Soil population densities were consistently associated with seed yield during the 1991 season and at some dates during the 1992 season, whereas nematode densities in the roots were not associated with yield in either season. In both seasons at 16-weeks after planting, total (adults + juveniles) H.columbus/100 cm3 of soil were significantly (P =0.05) correlated with soybean seed yield.