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White scale (Plate 45) derives its name from its appearance on the plant. The causative insects, Aulacas-pis rosae or Diaspis rosae, begin life as very small winged creatures. After mating they become sedentary, lose their wings, and degenerate into enormously distended bags of eggs, protected by a shield, or scale, that is impenetrable to water, frost, and sprays. Shade and overgrowth by weeds or annuals predispose to infection. The more sheltered, older parts of the roses are the most frequent sites of attachment.

Close examination will reveal the large number of component scales in what at first will have appeared to be one scale. Each scale is only about one-twelfth of an inch in diameter, but the colonies average about one-third of an inch in length and about one-sixth of an inch in width. The colonies in bad infestations cluster so closely that they overlap, making large areas of greyish-white colour.

From beneath each scale comes a young insect. Wingless females increase the spread of the disease on any already affected plant; winged females carry the scale to other roses. Males are all winged, and mate with either type of female.

The best mode of attack is to aim at sealing the scales and so prevent the insects from breathing. Red oil may be used as a spray or paint in winter, but it burns foliage at other seasons. White-oil preparations, kerosene emulsion, glue, or thin boiled starch may be used at any time. The under-surfaces of leaves and branches must not be missed; small patches can be scrubbed.

Red scale, due to Chrysowphalus aurantii, is most common on old plants in hot, dry weather. The female varies from yellow to reddish-brown, is round and has a small pedicle giving a ringlike central marking. The male is ovoid in contour, much smaller, and winged. Red scale is much less common than white scale; it feeds in the same way, by sucking, and can be controlled by the same means.

San Jose scale (Aspidiotus ferniciosus) infects roses only occasionally, but can be very destructive. The adult female scales are round and grey, with raised golden centres. Young scales are smaller and darker. The male scale is oval and only about half as long as the diameter of the female scale. Control measures are the same as for white and red scale.