516 ANNUAL, REPORT OF THE Off. Doc. 



the pump Will not suffice. The problem of sufficient agitation is thus 

 rendered doubly important, for without more satisfactory agitating 

 devices than those now in general use, it m extremely difficult to se- 

 cure a uniform distribution of the poison. And without a uniform 

 distribution of the poison perfectly satisfactory results are impos- 

 sible: the first portion sprayed out of the tank will be too weak to 

 do effective work, while the last portion will be strong enough to 

 injure the leaves, or in case the agitator is very poor the bulk of the 

 poison will remain on the bottom and sides of the spray tank. 



When Paris green is used in combination with Bordeaux mixture 

 to form a combined insecticide and fungicide, the rapid-settling objec- 

 tion to this otherwise valuable poison is very largely overcome. The 

 grains of the green become mixed with the floccular precipitate of the 

 Bordeaux mixture, and settle slowly with it. A few of the heavier 

 or larger grains go straight to the bottom, as they all do when the 

 poison is used alone, but the great majority remain in suspension 

 with the Bordeaux mixture. 



Substitutes for Paris Green. 



The many failures resulting from the use of impure Paris green, 

 and the prevalence of the low-grade qualities of the poison put upon 

 the market, have led to the introduction of other insecticidal poisons 

 for use as substitutes. These are practically all arsenites, and there- 

 fore, like Paris green, have arsenic as their active poisonous prin- 

 ciple. These poisons seem peculiarly virulent to insect life, and this 

 fact, together with their usual insolubility in water, make them the 

 most valuable class of compounds for this purpose. Some of these, 

 notably the arsenite of lime (arsenic, sal-soda and lime mixture), the 

 arsenate and arsenite of lead, are steadily growing in favor, especi- 

 ally when home-made. These have been successfully used by a num- 

 ber of growers and unless manufacturers of Paris green are more 

 careful to supply a reliable and satisfactory article, it is safe to say 

 these substitutes will largely supplant Paris green in the future. 

 The home-made mixtures possess the additional advantage of being 

 much lighter grained than Paris green, and therefore they can be 

 kept in suspension very much more easily. This is especially true of 

 the arsenate of lead, which, when freshly prepared, forms a milky 

 precipitate which will remain in suspension for a long time without 

 agitation. In addition, the lead compounds may be used very much 

 stronger without danger to the foliage, a fact which makes them par- 

 ticularly valuable for use on the foliage of the stone-fruits— notably 

 peaches and plums — which are notoriously sensitive to sprays of all 

 kinds. 



