38 INSECTS INJURIOUS TO VEGETABLES 



mixing 2 to 2^ ounces of the poison with 15 gallons of water. 

 The poison is first dissolved in 2 gallons of water, and more 

 is added to make 15 gallons. This is allowed to stand 5 or 6 

 hours, and the solution agitated several times. This is a fun- 

 gicide as well as insecticide, and is useful both for potato scab 

 and the potato scab gnat. Seed potatoes are soaked from an 

 hour and a half to three hours in this solution before planting. 

 As corrosive sublimate is a violent poison, unusual care should 

 be exercised in handling it. It should not be mixed in metallic 

 vessels, nor exposed where it might be eaten by stock. 



Formalin is prepared by mixing 8 ounces of 40 per cent, 

 solution with 15 gallons of water, and is used for the same 

 purposes as corrosive sublimate, but is less poisonous. Seed 

 potatoes are immersed two hours. 



Soap preparations. — Soap solutions are valuable as washes in 

 the control of noxious insects. Both hard and soft soaps are 

 used, but "whale-oil" soaps, usually manufactured of fish-oil, 

 are of greatest value. A solution of fish-oil soap is prepared 

 by dissolving I pound of the soap in from 4 to 10 gallons of 

 water. On some hardy plants a strength of i pound of soap 

 to 2 gallons of water can be used, but this is harmful to delicate 

 plants and must be employed with caution. A wash of i pound 

 soap to 6 or 8 gallons is of most value for aphides, minute leaf- 

 bugs, leaf hoppers, and thrips, and some forms of small larvae. 

 These soaps possess no particular advantage, however, over 

 kerosene-soap emulsion and are, in fact, less effective against 

 vegetable-feeders. Castile or "neutral" soaps, among which are 

 ivory soap, are much used on plants grown under glass and as 

 a means of arresting the ravages of "red spider" and the same 

 insects that have been mentioned. 



Cold and hot -i^atcr are properly speaking contact insecticides 

 of value in the destruction of mimitc insects such as aphides. 

 A strong sjjray of ice cold water applied to louse-infested plants 

 is a very useful remedy, but hot water is still more effectual 



