Apply 2 litres of oil and 2.5 kilograms of washing soda in 100 litres of water in early December and late March for pink wax scale, and two sprays, two weeks apart in the December-February period for white wax scale. Avoid spraying during a heat wave, or when the plants are stressed for water, since the foliage may be burned in these situations. This control is equal to that obtained by insecticide alone and is not detrimental to the natural enemies that keep other scale pests in check. The spray must be applied after all eggs have hatched and the crawlers are in a vulnerable position on the leaf surface. If the oil spray is absorbed into the plant, injury will result.
Oils vary in their potential to cause phytotoxicity.
The lower the viscosity of the oil, the less likely it is to cause phytotoxicity. The lower the viscosity of the oil, the lower the number of carbon atoms in each molecule of oil. For example, an oil with 21 carbon atoms per molecule is less likely to be phytotoxic than an oil with 25 carbon atoms per molecule. The situation is complicated by the fact that all oils have a range of molecules with different numbers of carbon atoms. As the range of molecules with different numbers of carbon atoms is reduced, there is less chance that the oil will contain a number of molecules of sufficient size to damage the plant.