194 MANUAL OF GARDENING 



arsenical poisons on plants or fruits soon to be eaten, as on currants 

 and gooseberries for the currant-worm. 



Tobacco. — This is a valuable insecticide and is used in several 

 forms. As a dust it is used extensively in greenhouses for plant-lice, 

 and in nurseries and about apple trees for the woolly aphis. Tobacco 

 decoction is made by steeping or soaking the stems in water. It is 

 often used as a spray against plant-hoe. Tobacco in the form of ex- 

 tracts, punks, and powders is sold under various trade names for use in 

 fumigating greenhouses. (See page 188.) 



Kerosene emulsion. — Hard, soft, or whale-oil soap, \ lb. ; water, 

 1 gal.; kerosene, 2 gal. Dissolve the soap in hot water; remove from 

 the fire and whils stiU hot add the kerosene. Pump the liquid back 

 into itself for five or ten minutes or until it becomes a creamy mass. 

 If properly made, the oil will not separate out on cooling. 



For use on dormant trees, dilute with 5 to 7 parts of water. For 

 killing plant-lice on foliage dilute with 10 to 15 parts of water. Crude 

 oil emulsion is made in the same way by substituting crude oil in 

 place of kerosene. The strength of oil emulsions is frequently indi- 

 cated by the percentage of oil in the diluted liquid : — 



For a 10% emulsion add 17 gal. of water to 3 gal. stock emulsion. 

 For a 15% emulsion add 10^ gal. of water to 3 gal. stock emulsion. 

 For a 20% emulsion add 7 gal. of water to 3 gal. stock emulsion. 

 For a 25% emulsion add 5 gal. of water to 3 gal. stock emulsion. 



Carbolic acid emulsion. — Soap, 1 lb.; water, 1 gal.; crude carbolic 

 acid, 1 pt. Dissolve the soap in hot water, add the carbolic acid, and 

 agitate into an emulsion. For use against root-maggots, dilute with 

 30 parts of water. 



Soaps. — An effective insecticide for plant-lice is whale-oil soap. 

 Dissolve in hot water and dilute so as to obtain one pound of soap to 

 every five or seven gallons of water. This strength is effective against 

 plant-lice. It should be applied in stronger solutions, however, for 

 scale insects. Home-made soaps and good laundry soaps, like Ivory 

 soap, are often as effective as whale-oil soap. 



Miscible oils. — There are now on the market a number of prepara- 

 tions of petroleum and other oils intended primarily for use against 

 the San Jos6 scale. They mix readily with cold water and are immedi- 



