Grapes 



199 



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. 



Mealy Bugs are best destroyed by fumigation with hydrocyanic acid 

 gas as follows: On dormant Vines, for every 100 cub. ft., use ^ 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 \ 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. 



Other Vine Pests. The Grape-fruit Fly (Drosophila melanogaster), 

 Vine Scale (Pulvinaria vitis), and the Phylloxera (Phylloxera vastatrix), 

 which has now and again occurred in England. [F. v. T.] 



Powdery Mildew of the Vine ( Uncinula spiralis). This very destruc- 

 tive disease was first noticed in a vinery at Margate in 1845, and within 

 a very few years it had 

 invaded Europe, Syria, 

 Asia Minor, and Algeria, 

 and, as usual on the first 

 introduction of a new dis- 

 ease, caused very serious 

 in j ury for some years. For 

 many years the summer 

 fruit of the fungus alone 

 was known in Europe, 

 and was called Oidium 

 Tuckeri. Of late years, 

 however, the winter fruit 

 has also been found, spar- 

 ingly. The latter is com- 

 mon on native plants in 

 Japan and the United States. This is one of those parasites where the 

 spawn or mycelium does not enter into the tissues of the plant, but forms 

 a thin white film on the upper surface of the leaves, young shoots, flowers, 

 and fruit. After a time these mildewed patches become densely covered 

 with the white spores, and look as if they had been powdered with flour. 

 This powdery appearance serves to distinguish the present from another 

 white mildew attacking the Vine. When young leaves are attacked, growth 



Fig 391. a, Mildew of Grapes, Uncinula spiralis. b, The summer 

 form (Oidium Tuckeri) with conidia germinating ( x 200) 



