310 PRINCIPLES OF SPRAYING 



To Fight Biting Insects. — Many insects live on the surface of 

 plants, eating twigs, leaves, fruit, etc. They bite their food and 

 also obtain some of the poison material which, if strong enough, 

 will kill them. 



Poison Sprays. — Arsenic is the chief ingredient of most of the 

 poison sprays. It is used in many different forms. The chief forms 

 are white arsenic, Paris green, London purple, arsenate of lead, and 

 arsenite of zinc. Hellebore is a native poison made from the plant 

 by that name. 



White arsenic is probably the cheapest form in which arsenic is 

 sold. It is a white powder readily soluble in water, but is very 

 injurious to the foliage, and can seldom be used successfully on 

 plants when they are in leaf. It is used as one ingredient of spray- 

 ing when combined with Bordeaux mixture. Prepare it by using 

 two pounds of sal-soda in one gallon of water. Add one pound of 

 white arsenic. When it is mixed into the form of a paste boil until 

 dissolved. Add enough water to replace that boiled away and 

 make the gallon of stock solution for use with Bordeaux mixture. 

 Use one quart of it with each 50 gallons of Bordeaux mixture for 

 orchard trees. If there is enough lime in the Bordeaux mixture it 

 will prevent the burning of foliage by the arsenic. 



A similar stock solution may be made with half as much sal-soda. 

 Then add to this mixture two pounds of fresh, unslaked lime. Add 

 enough water to make two gallons of stock solution including the 

 lime after slaking. Use two quarts of this stock solution to every 

 50 gallons of water. If the lime is good it should prevent most of 

 the injury to leaves, as the lime takes up the free arsenic. 



Pons Green. — This is a compound which is not uniform in com- 

 position. The national law requires at least 50 per cent of arsenious 

 oxid. There must be three and one-half per cent of water-soluble 

 arsenious oxid. 



Paris green is abundantly used in spraying orchards by mixing 

 one-half pound to 100 gallons of Bordeaux mixture, or one-half 

 pound to 100 gallons of water, to which about one pound of fresh 

 lime is added. The lime in either case is enough to take up the 

 free arsenic and prevent burning of foliage. Paris green is also 

 used as a mixture with lime-sulfur as a summer spray. It may 

 be combined with the lime-sulfur for the winter spray, but is 

 seldom used at that time as it is not needed. The use of Paris 

 green as an arsenical poison is rapidly being replaced by arsen- 

 ate of lead. 



