Nematode population densities were monitored and carrot yields and incidence of defects were assessed on three farms, one under organic management. The lowest proportion of marketable carrots and the lowest mean carrot weight were observed at the organically managed farm. Initial population densities of most nematodes were higher at the organically managed farm especially those, such as Meloidogyne javanica, known to be damaging to carrots. The tray method was reliable for assessing high nematode population densities at planting but was unreliable for detecting M. javanica in fumigated soil until 14 to 17 weeks after planting. Metham sodium (at 300 L/ha) was inadequate to provide effective control of nematodes, especially in early-season crops. Nematodes with high multiplication rates (> 5) over the growing season included M. javanica, Hemicycliophora saueri, Helicotylenchus spp., Scutellonema brachyurum and Paratrichodorus spp. The proportions of forked, galled, constricted and split carrots, and the weight of unmarketable carrots, were correlated with population densities of M. javanica in soil. The proportions of constricted and misshapen carrots were strongly correlated (adjusted r² 0.73–0.84) with population densities of H. saueri in soil. The proportion of split carrots and weight of unmarketable carrots were also correlated with population densities of H. saueri.