The use of chemical soil treatments to control the nematode, Longidorus elongatus, which transmits raspberry ringspot and tomato blackring viruses was studied in a 4-year field trial.
In untreated soil, after an overwinter fallow, the nematodes lost their infectivity, but regained it in the spring from germinating infected weed seeds. In soil treated with D-D (with or without a surface seal of solubilized xylenols) at 400 lb./acre, 95 % of the L. elongatus were killed. This treatment, and that with 20% quintozene at 1200 lb./acre, prevented transmisson of virus to Talisman strawberries throughout the 4-year experiment.
In both treated and untreated soils, L. elongatus populations increased about fourfold each year after strawberries were planted but, because of the initial kill, the populations in the D-D plots at the end of the experiment were approximately only one-eighth of those in the control plots.
After the first year, both D-D and quintozene treatments led to significant increases in crop, reaching 130% in the third fruiting season.
Metham-sodium and thiram, at the doses used, were only partially effective as nematicides: by the end of the second growing season the numbers of L. elongatus in the plots receiving these treatments equalled those in the untreated soil, and the infectivity had returned almost to its original level.