Changes in a Heterodera rostochiensis population through the growing season

SUMMARY Changes in the numbers of all stages of Heterodera rostochiensis in plants and soil were studied in a potato crop growing on infected land. Hatching and invasion occurred early in the season, when plants were very young and temperatures were below those considered necessary for hatching and invasion in Long Island, U.S.A. More larvae hatched from cysts nearer than away from potato roots. Males were abundant during June and July, when fertilization probably occurs. Many new cysts appeared during late June and early July. In May/June, there were many larvae in the roots of young plants but later there were few; a slight increase during August probably indicated a small second generation. The larvae for this second invasion may have come from the most recently formed cysts, which may have been stimulated to hatch either by root exudates or by substances from other soil organisms.