184 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



The action is complete in a quarter of an hour (Dubray), three- 

 quarters of an hour (Ritzema Bos), and five hours to destroy kermes 

 (Heh). Johnson says that disinfection is complete in a very short time, 

 and that with ten apparatus, 200 trees may be disinfected in a day, the 

 operation lasting half an hour. A method much in vogue in America 

 consists in disinfecting the roots of young nursery plants as far as the 

 crown. For this purpose all the trees are dug up, and placed in 

 closed cupboards or chambers in which prussic acid is disengaged ; 

 10,000 3'oung trees can be disinfected in this way at a time. Dr. 

 Koenig has introduced the practice of this style of disinfection at the 

 Agronomical Station of Nice, where it is employed for vines, ornamental 

 plants, as well as the branches of ornamental plants intended for ex- 

 portation. Waite and Howard recommend for the disinfection of 

 purchased trees hermetically sealed cupboards, in which they are en- 

 closed for an hour in an atmosphere of prussic acid before replanting ; 

 although the majority of plants resist the action of these poisonous 

 vapours it is preferable to operate during the repose of vegetation, for 

 in that condition they resist stronger doses capable of destroying the 

 parasites and their eggs. The action may be prolonged, and even last 

 an hour. The result is only the more complete. Tuille recommends 

 for the destruction of the larvte of the cockchafer (Melolontha vulgaris, 

 L.) to plough in colza or mustard during the flowering season along 

 with a ton of gypsum or lime per hectare (8 cwt. per acre). Amongst 

 the poisonous gases given off in consequence of the fermentation of 

 these plants is sulphuretted hydrogen, but also a certain amount of 

 prussic acid. 



Scolytides. — In America prussic acid is regarded as an excellent 

 substance for destroying the insects which dig galleries in the trunks 

 of trees. It may iDe applied at the moment the Scolytides or the 

 Bostriches attack the young trees. 



Wasps. — Gardner recommends the use of a solution of 120 grammes 

 in a litre of water (1'2 lb. per gal.). A plug of waste is attached to 

 a rod dipped in this solution, then introduced into the orifice of the 

 nest of wasps. The effect is instantaneous. 



Nematus Bibesii, Scop, (gooseberry saw-fly). — The highly voracious 

 larvie of this saw-fly are destroyed in Canada by cyaniding, working 

 under small tents as already mentioned. The gas acts in fifteen 

 minutes. To destroy the butterflies injurious to cotton plantations, 

 Mally plants haricot beans between the rows. As soon as the latter 

 are in flower they are sprayed with a dilute solution of potassium 

 cyanide. That kills the butterflies which settle on the flowers. 



Carpocapsa poiiiojiella (the codlin moth). — It is in winter that 

 fumigation under a tent with prussic acid may be very effectual. The 

 process is in common use in Canada. 



Diplosis violicola, Coquillet (violet fly). — Chittenden advises treat- 

 ing the violet stocks with potassium cyanide, so as to kill the larvifi of 

 this fly. 



Phylloxera rastatrix, Planch, (phylloxera of the vine). — Expert- . 

 ments on the pJiylloxera action by contact. — A phylloxera-infected root 

 was immersed for two minutes in a 1 per cent solution of potassium 



