190 MANUAL OF GARDENING 



place near the door. By cutting all the cords at once the 

 cyanide will be lowered into the jars and the operator may 

 escape without injury. Let the fumigation continue all 

 night, locking all outside doors and placing danger signs on 

 the house." 



In greenhouses, the white-fly on cucumbers and tomatoes may 

 be killed by overnight fumigation with 1 oz. of potassium cya- 

 nide to every 1000 cu. ft. of space; or with a kerosene emulsion 

 spray or whale-oil soap, on plants not injured by these materials. 



The green aphis is dispatched in houses by fumigation with 

 any of the tobacco preparations; on violets, by fumigation with 

 I to f oz. potassium cyanide for every 1000 cu. ft. of space, 

 leaving the gas in from J- to 1 hr. 



The black aphis is more difficult to kill than the green aphis, 

 but may be controlled by the same methods thoroughly used. 



Soaking tubers and seeds. 



Potato scab may be prevented, so far as planting infected 

 '' seed " is concerned, by soaking the seed tubers for two hours 

 in 30 gal. of water containing 1 pt. of commercial (about 40 per 

 cent) formahn. Oats and wheat, when attacked by certain 

 kinds of smut, may be rendered safe to sow by soaking or 

 mixing with similar or weaker solutions. It is probable that 

 some other tubers and seeds can be similarly treated with good 

 results. 



Potatoes may also be soaked (for scab) one and one-half 

 hours in a solution of corrosive sublimate, 1 oz. to 7 gal. of 

 water. 



Spraying. 



The most effective means of destroying insects and fungi 

 however, in any general or large way, is by the use of various 

 sprays. The two general types of insecticides have already 

 been mentioned — those that kill by poisoning, and those that 



