518 PREVENTION AND DESTKDCTION OF INSECT PESTS. 



The soft-soap should be also boiled, and then added to the strained 

 extract of quassia ; after both have been well mixed, they may be 

 added to the 10 gallons of warm water. 



6. Caustic washes are used with great success in the winter as 

 agents for ridding the bark of trees of their vegetal incumbrances. 

 The best wash is made by mixing 2i lb. of caustic soda with 10 

 gallons of water. It must not be used until the sap is well down 

 the tree. Trees washed with this soon present a clean healthy 

 appearance, and can be told at once. 



Fumigation. — This treatment is used for nursery-stock and plants 

 under glass. For this purpose (1) Hydrocyanic acid gas is used, 

 also (2) Tobacco, and (3) Pyrethrum. The first is most useful for 

 nursery-stock and dormant plants — it kills all life. 



F(3r every 100 cubic feet of space use f ounce of potassium cyanide, 

 and for each ounce of the cyanide use one liquid ounce of sulphuric 

 acid, mixed with 4 ounces of water. The cyanide is dropped by 

 special apparatus into the acid and water, and at once the deadly 

 fumes arise. Plants are best treated in a, dull light, dry tem- 

 perature, and at about 60° F., and should be exposed to the fumes 

 for at least an hour. The fumigating chamber or houses must not 

 be entered until all the gas has escaped, and this should be allowed 

 to do so from above. If sodium cyanide is used, then a \ ounce 

 is required. One must remember that this gas is a deadly poison, 

 and so it must be employed with extreme caution. 



Soil Fumigation. — In killing insects under ground, bisulphide of 

 carbon is employed. It is injected into the soil by means of the 

 Vermorel Injector at the rate of 4 ounces to the square yard, as 

 many small injections as possible. Being heavier than air, it sinks 

 into the soil, and is fatal to insect life that it reaches. It is also 

 used for fumigating grain, &c., and must then be placed at the top 

 of the grain. Remember it and its gas are poisonons and highly 

 inflammable — no light, cigar, or live electric wire must go neai- it. 

 Various patent soil fumigants, such as vaporite, fumite, and apterite, 

 are used with success for most ground pests, as leather -jacket,s, 

 chafer larvse, surface larvae, and ants. 



The effect of artificial manures on insect pest.-i is often most marked. 

 Nitrate of soda and kainit are frequently of much service in destroy- 

 ing surface grubs, whilst on the other hand superphosphates have less 

 effect. Bone-meal and guanos encourage many insect pests. So(rti 

 forms an excellent deterrent to many leaf-eating beetles and onion 

 fly ; dusting over the seed leaves and broadcasting over beds of 



