INSECTICIDES AND FUNGICIDES 261 



The box or house should be as nearly gas-tight as possible, with a very 

 tight-fitting door. The water and sulphuric acid are placed in a deep open 

 crock, then the cyanide of potassium, broken up into pieces about as large 

 as a hickory nut, is poured into the crock and the door shut as quickly as 

 possible. The fumes must be left about the trees not less than forty min- 

 utes, and fifty minutes or an hour is better. Short exposures in badly con- 

 structed houses have sometimes resulted in the sending out of living San 

 Jose scale on trees. 



In the hothouse the gas must be used with very great care to avoid 

 injury to plants. Plants of the grass family (Graminece) endure more gas 

 than most others tested by the writer. Corn, timothy, blue grass and 

 the like are not very sensitive. The leguminous plants, such as clover, 

 sweet pea and cowpea, are very likely to suffer some injury with any but 

 yen- light doses, and on this account it is best to use the less hurtful 

 tobacco extract when practicable. The extract will not, however, destroy 

 the adults of all hothouse pests, and has no effect at all on the scale insects 

 nor on the immature white fly. 



FUNGICIDES 



When all has been said the number of fungicides approved by the 

 experience of practical and scientific men is very small. Many have been 

 recommended, but comparatively few have stood all the tests as to effective- 

 ness, convenience of application and cheapness. Some are cheap and only 

 slightly effective; some are difficult to prepare; others are too costly for 

 extensive use. 



Copper Sulpnate. At the head of the list stands copper sulphate, a 

 cheap, effective fungicide, commonly known as bluestone. This is the 

 active and most essential ingredient of Bordeaux mixture. Concentrated 

 solutions of it cannot be used alone on foliage because of their caustic action. 

 ID winter on dormant trees it is sometimes used for fungous troubles, about 

 twc pounds being dissolved in a barrel of water. A weaker solution 1 

 pound in 200 gallons of water may be used on foliage in summer when 

 fruit is well matured and it is not desirable to use sprays like Bordeaux 

 mixture, which leave a residue. The bluestone may be quickly dissolved 

 by pouring boiling hot water over it. When one is not hurried it may be 

 dissolved by suspending in a loose sack in the water. It dissolves slowly 

 if simply thrown in the water and allowed to settle. 



To avoid to some extent the delays involved in dissolving bluestone it 

 is well to buy a finely powdered grade now manufactured for the making 

 of fungicidal preparations. 



Bordeaux Mixture. A standard formula for the preparation of this 

 valuable mixture is the following: 



Bluestone 4'pounds 



Fresh lime 4 pounds 



Water 50 gallons 



