This section is from the book "The Standard Cyclopedia Of Horticulture Vol2", by L. H. Bailey. See also: Western Garden Book: More than 8,000 Plants - The Right Plants for Your Climate - Tips from Western Garden Experts.
Emulsions are oily or resinous sprays in which these substances are suspended in water in the form of minute globules, a condition brought about by the addition of soap. They form an important class of contact insecticides, useful particularly against scale insects and plant-lice.
Kerosene emulsion is the oldest of our contact insecticides. It is especially valuable for use against plant-lice and other small, soft-bodied insects. It is prepared by the following formula: Soap, one-half pound; water, one gallon; kerosene, two gallons. Dissolve the soap in hot water; remove from the fire and, while still hot, add the kerosene. Pump the liquid back into itself for five or ten minutes or until it becomes a creamy mass. If properly made, the oil will not separate on cooling. For use on dormant trees, dilute with five to seven parts of water. For killing plant-lice on foliage, dilute with ten to fifteen parts of water. - Crude-oil emulsion is made in the same way by substituting crude oil in place of kerosene. The strength of oil emulsions is frequently indicated by the percentage of oil in the diluted liquid: for a 10 per cent emulsion, add seventeen gallons of water to three gallons of stock emulsion; for a 15 per cent emulsion, add ten and one-half gallons of water to three gallons of stock emulsion; for a 20 per cent emulsion, add seven gallons of water to three gallons of stock emulsion; for a 25 per cent emulsion, add five gallons of water to three gallons of stock emulsion.
Distillate emulsion is widely used in California. Distillate (28° Baume), twenty gallons; whale-oil soap, thirty pounds; water, twelve gallons. Dissolve the whale-oil soap in the water which should be heated to the boiling point, add the distillate and agitate thoroughly while the solution is hot. For use, add twenty gallons of water to each gallon of the stock solution.
This spray is used in California for mealy-bugs, plant-lice, and the soft brown scale: Whale-oil soap, forty pounds; crude carbolic acid, five gallons; water, forty gallons. Dissolve the soap completely in hot water, add the carbolic acid, and heat to the boiling point for twenty minutes. For use, add twenty gallons of water to each gallon of stock solution.
There are now on the market a number of concentrated oil emulsions, known as soluble or miscible oils, intended primarily for use against the San Jose scale. For this purpose they are fairly effective when diluted with not more than fifteen parts of water. To lessen danger of injury to the trees, applications should not be made when the temperature is below freezing, nor when the trees are wet with snow or rain. Methods have been devised for preparing these concentrated emulsions at home, but as there is considerable danger attending the process, it is better to buy them ready-made.