AbstractIn laboratory experiments, D-D, dazomet and quintozene gave good control of Longidorus elongatus and Xiphinema diversicaudatum and largely prevented virus transmission by them. Treatments were equally successful at 7, 14.5 and 22°C. Methomyl, at the normal rates used, was only slightly nematicidal but completely prevented the transmission of virus. In a field experiment, methomyl prevented virus transmission in a rye-grass crop for only a few months and L. elongatus populations in the treated plots were as high as those in untreated ones; D-D and quintozene were the most effective treatments. In laboratory experiments, low concentrations of methomyl were shown to cause a continuous nervous excitation of muscular contraction in the nematodes, but high concentrations were immediately toxic.