Insecticides 



207 



fruits free from discoloration, it may be advisable to 

 use the ammoniacal carbonate of copper solution. 

 This material is ordinarily somewhat cheaper than the 

 Bordeaux mixture, but it does not adhere so long, 

 and its practical fungicidal value is generally not con- 

 sidered to be so great. 



It is not every kind of plant disease which is 

 destroyed or averted by means of Bordeaux mixture or 

 other sprays. Whenever the whole plant wilts or seems 

 to be affected internally, it is probable that there is 

 some injury at the root or in some part of the main 

 stem. The trouble in this case may be due to root 

 insects, borers or to some bacterial or other internal 

 trouble w^hich cannot be reached by external applica- 

 tions. In these cases the man has no recourse except 

 to destroy the affected plants, and then by means of 

 strategy to avoid the recurrence of the trouble. 



For insects^ arsenic and kerosene (coal -oil) are the 

 leading remedies. Of insects which feed on the ex- 

 ternal parts of the plant, there are two general kinds, 

 so far as their manner of eating is concerned, — the 

 chewing or biting insects, as the beetles and larvaB 

 (worms), and the sucking insects, as the various 

 scales, plant-lice and squash-bug. Insects of the for- 

 mer type are dispatched by poisoning their food. 

 This is usually done by spraying the plants with Paris 

 green or some other arsenical poison. Insects of the 

 second type comprise those which suck the juices of the 

 plant and must be destroyed by some material which 

 kills them by contact. Of these materials, the chief are 

 the various kerosene preparations and whale-oil soap. 



