Tulip-root of oats, caused by the eelworm Ditylenchus dipsaci, has been controlled satisfactorily by surface treatment with 40 to 50 gallons per acre (450 to 653 Kg. per hectare) of I in 1,000 mercuric chloride solution. This was applied from a suitable fan-jet sprayer followed by a surface-mixing device, several forms of which are mentioned. The treatment was fully economic and resulted in a full yield when given to lightly infested oats grown in a rotation having a previous history of severe infestation. Surface treatments on severely infested fields gave increases in yield but not a full crop. Treatments were given immediately a f ter sowing the oats; increased rates of application brought no enhanced control, whilst treatment with half the volume of liquid was ineffective.