Chemical treatment of soil to prevent transmission of tobacco rattle virus to potatoes by Trichodorus spp

SUMMARY Of the chemicals tested in field experiments at two sites on sandy soil in Scotland, D‐D (dichloropropane‐dichloropropene) applied before planting at 200 or 400 Ib/acre (224 or 448 kg/ha) gave the best control of potato spraing disease caused by tobacco rattle virus (TRV); it almost eliminated the disease in the first year and greatly decreased the incidence in the second. Application in the autumn was more effective than in the spring. Methomyl at 8 Ib/acre (9 kg/ha) and dazomet at 150 Ib/acre (168 kg/ha) greatly decreased the spread of TRV in the first year after treatment, but not in the second. These effects were closely related to the nematicidal effects of the chemicals on the nematode vectors (Trichodorus spp.), except that methomyl controlled virus spread more effectively than it killed Trichodorus. When data from plots treated with methomyl are excluded, spraing incidence was more closely correlated with the numbers of Trichodorus found in May than in September. In general, the infectivity of soil, estimated by infection of cucumber bait seedlings with TRV in pot tests, paralleled the incidence of spraing, but bait cucumber roots were infected more readily than potato tubers. Application of D‐D at 200 Ib/acre (224 kg/ha) is probably worthwhile economically when potato cultivars that are susceptible and sensitive to TRV are to be grown on land infested with the virus.