The population dynamics of Heterodera trifolii in a Manawatu pasture

Abstract

Changes in numbers of all stages of clover cyst nematode Heterodera trifolii in white clover roots and in soil were studied in a white clover/ ryegrass permanent pasture Soil samples were taken with a soil corer at fortnightly intervals between March 1999 and March 2001 There were two distinct cycles of H trifolii invasion and development in a year Distinct peaks in numbers of J2 in soil were seen in late winter and again in late summer followed by peaks in J2 numbers in roots possibly reflecting optimum soil temperatures in spring and autumn The numbers of females peaked 24 weeks after those of J2 in roots No distinct peaks were found in the numbers of new and old cysts Amounts of clover root in cores were generally higher in autumn and in spring Numbers of all stages of H trifolii and weights of clover root tended to be lower in 2000 than in 1999