Control of potato cyst nematode (Globodera rostochiensis) by nematicides and a resistant potato cultivar at four sites in Scotland

SUMMARY The control of potato cyst nematode (Globodera rostochiensis) by the oxime‐carbamates aldicarb and oxamyl was tested in four fields in Scotland. Dazomet was tested in three of these fields and carbofuran in one. In untreated plots in the three most heavily infested fields Maris Piper (resistant) yielded better than Pentland Crown (non‐resistant). All nematicides increased the yields of both potato cultivars but had a greater effect on the yield of Pentland Crown. Dazomet increased yields of tubers most. Heavy nematode infestation reduced yield of tubers more in a sandy soil than in two sandy loams. In a field with few potato cyst nematodes nematicides did not significantly affect tuber yields. Although the nematicides greatly increased yields, they were not completely effective in controlling potato cyst nematodes. In treated plots in the lightly infested field, there were more nematode eggs following a crop of Pentland Crown than before. In contrast, Maris Piper markedly decreased post‐cropping populations and except at one site, where dazomet further decreased nematode numbers, combining nematicides with the resistant cultivar failed to decrease nematode numbers further. Nematicides decreased the numbers of larvae invading potato roots by up to 95%, oxamyl at 5–6 kg/ha being consistently the best treatment.