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 acarus is related to the mite causing the Big Bud in the Black Currants, but it lives in a different way.
The mite is the cause of the numerous pale blister-like galls one frequently sees on Pear leaves. These leaf galls are each caused by a single minute Eriophyes which enters the leaf by the stomata or breathing pores. In the soft leaf tissue they breed, and as the tissue becomes destroyed they spread farther and farther over the leaves and branches. The galls turn black later, and the whole leaf may die or more usually falls off. Young fruitlets are also attacked and ruined by small reddish blister-like galls being formed on them.
The acari all winter under the bud scales, and as soon as the buds commence to burst get out on to the leaves or blossoms and enter the tissue. For many years this mite did little harm, as it increased so slowly, but recently it has spread in some places with great rapidity, and has done much damage.
Treatment consists of late winter spraying with the following: Quicklime, 6 lb.; sulphur, 3 lb.; salt, 3 lb. Mix these together and enough water to slake the lime. Whilst still hot add more water and boil for forty-five minutes, then add sufficient water to make up to 10 gall.
Another wash is made by adding to the above 1 lb. of caustic soda. The soda and lime are mixed together and slaked in hot water in which the sulphur has been incorporated. This requires no boiling. If the pest continues it is necessary to summer spray with paraffin jelly.