Kerosene Emulsion. - The scale insects, plant-lice, and the true bugs (Heteroptera) that suck their food from the leaves or young growth of plants and trees cannot be controlled by spraying with the arsenites or other poisons used for the bud- and leaf-eating insects. The leading remedies for this numerous family are whale-oil soap, kerosene emulsion, and infusions of and powdered tobacco. But the standard solution that can be used profitably on all types of the sucking insects is kerosene emulsion. Kerosene has been used for many years in a pure state by carefully applying it to the insects or wiping them from the leaves and stems with a cloth moistened with kerosene. The next move was to mix it with water for spraying. But not until soap or oil was added to the solution could a perfect mixture of the oil and water be effected. It is said that dealers in kerosene, when it commanded a higher price than at present, first made the discovery that oil and soft water would mix when a solution of soap was added. The use of the kerosene emulsion was quite common, when the writer visited west and east Europe in 1882, for the destruction of the several species of aphis in greenhouses, and at Proskau in north Silesia it was used for the bark and leaf lice of the orchard fruits. In this country the first one to use it known to the writer was Professor Cook, then professor of entomology at the Agricultural College of Michigan. During a visit to the Michigan station in 1878 the writer was shown the beneficial effects of spraying for sucking insects with a mixture of kerosene and soapy water.
The usual formula for making kerosene emulsion is to shave one half pound of ivory soap or whale-oil soap in one gallon of soft water and boil until dissolved. The kettle is removed from the stove and while boiling hot two gallons of kerosene are added that has been previously warmed in the sun or in a warm room. The mixture is then agitated by active stirring for ten minutes. If not very hot the mixing is often effected by forcing it through the sprayer back to the vessel until it is creamy in color and will flow evenly down the sides of the pail or tub.
This stock mixture is diluted for use with from eight to fourteen parts of additional water. The apple- and pear-leaves when mature will bear an admixture to the stock of twelve or thirteen parts of water. But the stone fruits require a weaker solution of fourteen parts of water. In the dormant period spraying for aphis, to reach the eggs, only enough water is used to make it possible to use the solution in the sprayer.