In 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 22C. 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.