This is a common trouble with the apple orchards in about all parts of the Union. During the summer little can be done, as the insect is well housed under its scale. In the spring the scales cover a number of light-colored eggs that usually at the North hatch in May. When exposed the young insects may be seen in great numbers on the younger growth.
Before growth starts in the spring the eggs can be largely destroyed by spraying with kerosene emulsion made very strong. The kerosene and soap solution penetrates the scale and destroys a large proportion of the eggs. When the young insects appear in May the spraying is repeated with the emulsion of ordinary strength. This plan of spraying also destroys the woolly aphis and the scurvy scale-louse. It is not yet certain that the spraying in the dormant period with raw petroleum of good quality or a good grade of petroleum will harm the trees. The kill or cure methods of warring with the San Josť scale has seemed to demonstrate that petroleum and kerosene are not as harmful to the bark and buds of trees as had been suspected, and this agrees with the writer's experience on a smaller scale. But we have had more favorable experience on dormant trees in killing scale insects with kerosene and soap emulsion made with larger proportion of kerosene than usual than with the modern pumps using a mixture of kerosene and water, and far better than with whale-oil soap.
With proper care the scale-lice of the deciduous fruits can be controlled largely by spraying in the dormant season. But the different scale insects of the citrus fruits are not so easy to manage, as the persistent foliage prevents the use of kerosene or petroleum strong enough to penetrate the scales without injury to the leaves. Some of the least harmful species are kept in check by spraying when the insects are exposed with kerosene emulsion, whale-oil soap, or the resin solutions. But where the San Josť scale joins forces with other species the tent system with fumes of hydrocyanic-acid gas is the only certain method. In California parties with proper outfit make a business of clearing orchards of scale insects by this method. Nursery stock is now also fumigated with this gas in tight boxes or houses since the advent of the San Josť scale east of the Rocky Mountains.