FUMIGATION WITH HYDROCYANIC ACID OAS. 
303 
FUMIGATION WITH HYDROCYANIC ACID GAS* 
By Mr. H. H. Cousins. 
For Black Currant Bud-Mite and Mealy Bug. 
These two pests are widely recognised as among the most dangerous and 
elusive of the enemies of the greenhouse and garden. So severe have 
been the losses incurred by the spread of the Black Currant Mite that the 
industry is in a very critical state, and many hundreds of acres which 
once produced large and highly profitable crops have had to be " grubbed " 
and the culture of Black Currants abandoned. One grower recently 
informed us that his average returns from this crop had fallen from 
£^1,400 a year to nil, owing to the terrible havoc wrought by the mite. 
" Mealy Bug " is a well-known and widely dreaded foe of the vinery, and 
few are the gardeners who have succeeded in its complete destruction 
without the most drastic of remedies. 
" Washes " having proved of little use for these two pests, it became 
necessary to devise other means of attack. Reports of the great success 
of cyanide fumigation in America for the treatment of the San Jose Scale 
suggested a trial of this method, and the following experimental results 
justify a confident expectation [in regard to one of the pests, and a hope in 
regard to the other] that a successful means of attack has at last been 
found. 
1. Experiments on Black Currant Bud-Mite. 
The spread of the disease is clearly due, in the first place, to the propa- 
gation by cuttings from infested stock. Buds of apparently normal 
dimensions frequently contain a few mites capable of indefinite increase. 
In the case of the Baldwin Currant, it is most difficult to find a shoot free 
from mites even when the buds appear quite healthy. 
Secondly, diseased stock undoubtedly spreads the infection by the 
mechanical distribution of the mites on the clothes of the men engaged in 
hoeing, &c., or through the agency of the wind or of birds. 
Given a means of cure, this disease should be proclaimed as infectious, 
and every effort made to stamp it out. 
Preliminary experiments indicated that at least forty minutes' exposure 
to the cyanide fumes was necessary to ensure the complete destruction of 
the mites. Shorter periods were apparently successful at a first inspection, 
but a further examination showed that many individuals recovered after 
twenty-four hours. Doses of cyanide varying from 0*05 gramme to 
0'4 gramme per cubic foot were tested, and a minimum of 0*2 gramme per 
cubic foot was arrived at. A stronger dose than O'B is not called for. 
Fumigation of Cuttings and Young Bushes. 
On January 8, 2,000 diseased bushes which were intended for planting 
out were treated as follows : 
The bushes were tied in bundles and placed in a heap on the ground. 
* Reprinted by permission from the Journal of the Agricultural College, Wye,. 
Kent. See also R.H.S. Journal, vol. xxv. p. 298. 
