Ll. Lloyd 21 



Table V. Showing the mortality of A. vaporariorum obtained with 



tetrachlorethane. 



(3) Tobacco preparations. It was recently stated by a correspondent 

 in a trade journal that some twenty years ago when white fly first started 

 to give trouble to nurserymen in this country it was only necessary to 

 burn a little tobacco in the greenhouse in order to control it, but that 

 now such preparations only stupify it. Whatever they were once, they 

 are at any rate at present of very little use against the pest as they drive 

 enormous numbers of the insects outside and many of those which fall 

 are merely stupified. They have no appreciable effect on the young stages. 

 The various tests made will not be discussed in detail. They included the 

 burning of "shreds" at five times the strength recommended by the 

 maker, fumigations with a proprietary nicotine and camphor fumigant, 

 also with pure nicotine at the rate of | oz. per 1000 eft. and | oz. with 

 f oz. camphor per 1000 eft. In each case less than a 50 per cent, mor- 

 tality of the adidts was obtained. These preparations have also become 

 almost prohibitory in cost to the commercial grower. 



(4) Cyaniding. Fumigation with hydrocyanic acid gas or, as it is 

 generally called, "cyaniding" is the most effective method of controlling 

 the pest and is the only one known sufficiently economical for use in 

 trade nurseries. High grade sodium cyanide, 98 per cent, purity (often 

 described as 130 per cent, in reference to the strength of pure potassium 

 cyanide), is employed, and the gas is generated by means of sulphuric 

 acid. Potassium cyanide and phosphoric acid are sometimes used as 

 alternatives, but they have no advantages and are more costly. The 

 proportions in which to employ the materials are : 1 oz'. of sodium cyanide 

 in 1| fluid ozs. of sulphuric acid diluted with 3 fluid ozs. of water. An 

 error which had become almost universal among Lea Valley growers 

 and in other parts has led to most of the failures in the use of these 

 materials in the past. Fear of the poisonous nature of the gas has led 

 the users to drop the cyanide into the acid enclosed in a sealed envelope 

 or some other type of paper packet. When the acid enters the packet 

 and evolution of the gas commences the pressure prevents the free access 

 of the acid and the heat of the reaction chars the remaining cyanide. 



