170 Principles of Plant Culture. 



stock is now required by law in some localities to be 

 treated with hydrocyanic gas before shipment, to pre- 

 vent the dissemination of dangerous scale insects. 



298. Fir-Tree Oil is considerably used in greenhouses 

 and conservatories for destroying scale insects and the 

 mealy bug.* .It is mixed with warm soft water at the 

 rate of a tablespoonful of oil to a pint, and applied 

 with a syringe; or the plants are dipped into the 

 mixture. 



299. Hot Water may also be used for destroying the 

 above named insects (298) and plant lice (aphidas). 

 Infested pot-plants are inverted and immersed five or 

 six seconds in a vessel containing water at 120 F. 

 This treatment must be used with caution. 



Forcible syringing of plants with water is also an 

 excellent method of ridding greenhouse plants from 

 insects. 



300. Insect Attacks Sometimes Become Formid- 

 able from the vast number of the individuals. The 

 chinch-bug,t the army-worm$ and various species of 

 locusts or grass-hoppers sometimes devastate large 

 tracts of country. For the destruction of these insects, 

 special means must be employed. 



301. The Chinch-Bug may be controlled in a meas- 

 ure, by burning over all grass land early in spring, in 

 seasons when attacks are expected. The bugs may be 

 kept out of corn fields by plowing a furrow away from 

 the corn, on the side from which the attack is looked 

 for, and strewing stalks of fresh corn in this. As the 

 insects congregate on the corn in the furrow, they 



* Dactylopius. f Bllssus leucoplerus. I Leucania unipuncta. 



