This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This Aphis (fig. 346) forms a large quantity of white floc-culent wool from its back. It lives mainly on the bark of the trunk, branches, and finer shoots of the Apple, but now and again on Pear, and abundantly on the Wild Crab Apple. It also lives on the roots of Apple trees, where it works in a similar way to the aerial form, sucking out the sap, and by the punctures of their proboscis they cause boillike swellings on young wood, which burst and which later form large rough patches in the crevices of which the insects and others shelter.
The usual form is the plum-coloured wingless female, which is constantly producing pale-yellowish living young. In the summer a winged female brood may appear. The winter is passed amongst moss and lichen on the trees, under rough bark and grafting clay in the wingless female condition above ground, and also as wingless females below ground and on the roots near the butt of the trees. Now and again an autumnal sexual brood occurs, the oviparous female laying a single egg near the base of the tree, and her dried skin remains behind as a covering over it.
Fig. 345. - Apple Mussel Scale (Lepidosaphces ulmi).
Fig. 346. - Woolly Aphis or American Blight (Schizoneura lanigera).
Spraying with paraffin emulsion will destroy the aphis in summer and autumn above ground, but the washing must be done with force; a strong jet must be sent to hit the patches of aphis in the crevices. There is an intimate connection between the Woolly Aphis and canker (see p. 89).
The ground form may be attacked by injecting disulphide of carbon into the soil, 1/2oz. on four sides of the tree about 2 ft. from the trunk and about 6 in. deep, or the earth may be cleared away for 3 ft. around the trunk and the ground soaked with warm paraffin emulsion. In Australia, etc, it is found that the root form does not occur on " Northern Spy" or "Winter Majetin".