Tests were made of the solubility of a number of copper compounds in mineral and vegetable oils. Phytocidal tests on onion foliage showed that turpentine, pine oil and white spirit were damaging whereas cottonseed oil and white oil were innocuous. Copper salts in white oil, white spirit, turpentine or pine oil showed a higher fungicidal value than in cottonseed oil. In laboratory tests, a solution of copper 3:5-di-isopropyl salicylate was more fungicidal than Bordeaux mixture of the same copper concentration. In a small field trial, copper 3:5-di-iospropyl salicylate dissolved in white oil to give a concentration of 0.01% Cu was atomized three times at monthly intervals on to onion foliage without damage. The same material at 0.1% Cu in white oil was phytocidal. No control of onion downy mildew (Peronospora schleideniana) was obtained in this trial. The method of atomization was convenient and practicable for small-scale operation. It gave perfect wetting of the foliage and was very economical of material.