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.
Two Mealy Bugs attack the Vine. They can at once be told by longispinus having long lateral and tail processes, whilst citri has short ones. They live in any crevices on the Vines, and even amongst the fruit and under the skin of the rods and stems. They secrete a quantity of white wool at times, and their eggs are deposited under these woolly masses. Under glass they breed all the year round. The males are winged, and appear in the summer: they are reddish brown and mealy, with two iridescent blue wings and two long caudal filaments.
Fig. 390. - Scalded Grapes.
A, Bunch of Lady Downes (reduced); a, scalded side.
B, Partly scalded berry; 6, scalded portion.
All nat. size.
C, Shrivelled berry, after scalding.
D, Partly scalded berry; c, shrunken patch; d, seeds.
E, Sound berry at time of scalding.
F, Perfectly finished berry.
Mealy Bugs are best destroyed by fumigation with hydrocyanic acid gas as follows: On dormant Vines, for every 100 cub. ft., use 1/5 oz. of sodium cyanide, and for each ounce of cyanide 1 liquid oz. of sulphuric acid, previously diluted with 3 to 4 oz. of water; if potassium cyanide is used the proportion is 1/4 oz. (See Vol. I., p. 169.)
Care must be taken in using this deadly gas. The cyanide must be dropped into the acid and water so that the operator does not inhale any of the deadly gas generated. This can be done by special apparatus sold by horticultural sundriesmen. The fumigation should last forty-five minutes, and is best done towards the latter part of the day, and the house freely ventilated from above before anyone is allowed to enter.
Painting with paraffin and methylated spirit is also useful for this pest.