AbstractOxamyl applied to field soil at 5.6, 11.2 or 22.4 kg a.i./ha prevented Longidorus elongatus from acquiring and transmitting tomato black ring virus for at least 6 weeks, although the numbers of nematodes present were not greatly decreased. In glasshouse and laboratory tests, oxamyl at 1.0 ppm in the soil water largely prevented viruliferous L. elongatus from transmitting virus to bait plants over a period of one month. Xiphinema diversicaudatum infected with arabis mosaic virus was equally affected by smaller concentrations, 0.1 ppm being sufficient to inhibit virus transmission in one test. Inhibition of virus transmission was associated with a decrease in the number of root tip galls produced by nematode feeding, especially that of X. diversicaudatum. Few nematodes were seriously affected by oxamyl, except at the greatest concentration tested (100 ppm), when numbers of L. elongatus, but not X. diversicaudatum were decreased. Viruliferous nematodes treated with oxamyl in vitro protracted their stylets, but their subsequent ability to transmit virus was unimpaired.
L. elongatus and X. diversicaudatum were exposed either to raspberry ringspot virus, tomato black ring virus or arabis mosaic virus and the effects were assessed of oxamyl on their ability to transmit viruses to several test plants, including petunia and cucumber. Oxamyl applied to field soil prevented L. elongatus from acquiring and transmitting TBRV for at least 6 weeks, but nematode numbers were not greatly decreased. In glasshouse tests soil drenches of oxamyl at 0.1 or 1.0 p.p.m. largely inhibited virus transmission to test plants for 1 month. This effect was associated with a decline in the number of root tip galls resulting from nematode feeding, especially that of X. diversicaudatum. Nematode populations were little affected by low concentrations of oxamyl, but at 100 p.p.m. those of L. elongatus were reduced.