INSECTICIDES AND FUNGICIDES 265 



remains suspended much better than Paris green. It has the additional 

 advantage of adhering to leaves longer than Paris green, and thus fewer 

 applications are required. A single spraying with this substance, if applied 

 at the right time, is for some plants sufficient for a whole season. The 

 arsenate of lead paste is commonly used with water in the proportion of 

 2J to 3 pounds in 50 gallons. As found in the market it contains about 50 

 per cent of water. 



It requires more by weight to destroy insects than Paris green, but 

 the cost per pound is less and hence the actual cost for materials amounts 

 to about the same, whichever poison is used. Its advantages are so 

 decided in other directions that it is now supplanting Paris green in popular 

 favor. For the injuries of most gnawing insects working on foliage this 

 insecticide may be safely recommended. 



To meet the objections sometimes made to arsenate of lead paste, 

 a powdered arsenate of lead has recently been offered to the public by 

 manufacturers of insecticides. The paste when dried out is lumpy and is 

 not in this condition easy to mix with water. In the powdered form it is 

 not open to this objection and may, besides, be dusted over plants without 

 the addition of water. 



There are serious objections to the use of poisonous dusts, however, 

 though in practice they have advantages that always commend them to 

 workmen. The weight of the water to be carried when using liquid sprays 

 increases the labor, of course, and this ought to be lessened if it can be done 

 without diminishing the effectiveness of the applications, and also without 

 increasing the danger to those making the applications. The inhaling of 

 either dry Paris green or arsenate of lead is a serious matter, and if con- 

 tinued long is certain to lead to ill health. Liquid sprays go more directly 

 and evenly to the plants and stay there. They may be made just as 

 promptly effective as the dusts if used when the injury is beginning. They 

 are not so likely to be inhaled. 



Arsenite of Zinc. This poison has somewhat recently been recom- 

 mended as a substitute for Paris green and arsenate of lead, and appears 

 to be about equally good and somewhat cheaper than either. It is a finely 

 divided white powder as put on the market and remains in suspension 

 about as well as arsenate of lead, having thus some advantage over Paris 

 green. It contains a little water-soluble arsenic and has been claimed to be 

 less injurious to foliage even than arsenate of lead, possessing at the same 

 time about the same killing power. For use it is stirred first into a little 

 water and allowed to soak for a time, then is stirred into the water in which 

 it is to be used, about one pound of the powder being added to 50 gallons of 

 water. It contains nearly the same quantity of arsenic as Paris green. 

 Like arsenate of lead, it remains in suspension better if a little soap is 

 dissolved in the water into which it has been stirred. It has of late been 

 quoted by dealers at from 20 to 25 cents per pound. 



London Purple. This arsenite came into use for injurious insects 



