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.
Fig. 376. - Magpie Moth (Abraxas grossulariata) and Larva.
These acari are elongated, with four legs only in front and a ringed body with a few bristles. They are scarcely perceptible to the naked eye, but may be seen with a lens, especially in bright light. At their tail end is a kind of sucker. They live almost entirely inside the buds of the Black Currant, but now and then attack the Red and the White. Their presence in the bud causes it to swell abnormally and become bloated or globular in form. Large numbers of mites may be found in a single bud, where they breed. The eggs are comparatively large. As the buds die the acari migrate to other buds; this they do by both crawling and jumping, holding on to the outside of the bud by the terminal sucker. Birds, bees, etc, also carry them about. The young are much like the adults. Reproduction takes place most of the year, but less in February and the winter months than at other times. Migrations are frequent, but most numerous from April to June. A few mites have been found under the skin of the stumps left in the ground; these probably enter the new buds or young shoots.
The mites may kill the buds, which then turn brown and remain on the bushes, or the buds may burst but then seldom bear fruit.
The only satisfactory method is hand picking; this must be done about three times, namely, in autumn, spring, and late spring, and the buds carefully burnt. Certain varieties resist the mite more than others. The "Boskoop Giant" and French Currants withstand it well as a rule, whilst "Black Naples" and "Baldwins" suffer very severely. No spraying has proved to be completely successful, but results of benefit have been claimed by spraying six or seven times with soft soap and quassia in spring and early summer, and with three dustings of lime and sulphur. It is best, however, to rely on hand picking.