Observations on the control of potato cyst‐nematodes, Globodera rostochiensis and G. pallida in 35 English potato soils in pots by oxamyl and resistant potatoes

SUMMARY The increase of 35 English field populations of potato cyst‐nematodes (Globodera rostochiensis and/or G. pallida) was measured on Désirée, Maris Piper, Caxton (A25/11), Cromwell (A27/20) and clone 11233 ab 22 in pots of sandy, silty or peaty loam soil. Désirée was susceptible to all populations tested and, as in field soils, the final population (Pf) was inversely related to the initial population of potato cyst‐nematode eggs (Pi) in the soil. Maris Piper and Cromwell were resistant to all G. rostochiensis populations, with one possible exception. Maris Piper was susceptible to all G. pallida populations. Caxton was susceptible to some and fairly resistant to other populations of G. rostochiensis, indicating the existence either of two biotypes within the one pathotype (Rol) as yet encountered in Britain, or the existence of an additional pathotype. Caxton and Cromwell were fairly resistant to G. pallida. Clone 11233 ab 22 was only moderately resistant to both species. Resistance to potato cyst‐nematode increase varied considerably, especially in Caxton (to G. rostochiensis) and in 11233 ab 22 (to both species). Oxamyl greatly reduced the increase of G. rostochiensis populations on Désirée potatoes, with the notable exception of one population but it generally had much less effect on G. pallida populations, regardless of soil type. The difference in effect on the two species may be due to a longer period of hatching in G. pallida than in G. rostochiensis and also perhaps to a second generation in G. pallida.