SummarySpeed of emergence of juveniles from cysts in potato root diffusate (PRD)in vitrodiffered betweenGlobodera rostochiensisandG. pallidaand between populations within each species. Early emergencein vitrowas slower in most populations ofG. pallidathan in most populations ofG. rostochiensis. FewerG. rostochiensisjuveniles emerged from 4 or 6 month old than from 4 yr old cysts.MoreG. rostochiensisemerged in solutions of sodium metavanadate at concentrations of 10‐2and 10‐3M than in PRD and as manyG. pallidaemerged in the same solutions as in PRD. In plots of bare fallowed sandy loam, emergence ofG. pallidawas stimulated by 10‐‐3M sodium metavanadate. The emergence of two populations ofC. pallidain PRD was stimulated by the addition of benomyl at 0.1 ppm (3.4 × 10‐‐7m). In microplots, cv. Cara potatoes grown for 8 wk decreased four populations ofG. pallidaby up to 93%. During a 4 wk period in PRD, more than 20 juveniles per gravid female emerged from five of 25 populations ofG. pallida. In root observation boxes in which cv. Désirée was grown, oxamyl applied to the top 15 cm of a peaty loam soil greatly increasedG. pallidain soil 1545 cm deep. In another peaty loam, but not in a sandy loam, the same treatment appeared to increase the nematode in soil 15–30 cm deep. Oxamyl incorporated in the uninfested top 15 cm of all three soils largely prevented nematode increase from juveniles migrating upwards from untreated heavily infested soil 15–30 cm deep.These experiments suggest that inadequate control ofG. pallidaincrease on susceptible potatoes by an oximecarbamate nematicide of short persistence, such as oxamyl, is primarily due to the slow rate of juvenile emergence in most populations ofG. pallida, with a second generation and the upward migration of juveniles from deeper untreated soil later in the growing season as potential co