32 INSECTS INJURIOUS TO VEGETABLES 



dealers, e. g., with white arsenic, which makes the liquid mixture 

 (containing an excess of free arsenic) still more scorching m 

 its effects on vegetation. The New York (Geneva) Experiment 

 Station has ascertained that this insecticide possesses about one- 

 third the fungicide value of Bordeaux mixture. 



Arsenate of lead, lead arsenate or "disparene" has the ad- 

 vantage of being less harmful to growing plants and adheres 

 better to the leaves than other arsenicals. It is less apt to burn 

 delicate foliage, hence does not require the same care in its 

 application as is necessary for Paris green, and can, moreover, 

 be obtained ready made on the market. Numerous brands are 

 for sale, and care should be exercised to obtain a good quality 

 as some alleged arsenate of lead preparations contain free 

 arsenic. The commercial preparations are mostly like paste or 

 putty and must be worked in a little water in a bucket before 

 being added to the spray tank. 



It is prepared by combining acetate of lead (6 or 7 parts) 

 with arsenate of soda (3 parts). In spraying it can be employed 

 at any strength from 3 to as high as 12 pounds to 100 gallons 

 of water without injury to most vegetable crops. Its cost at 

 present writing is 12 to i^ cents a pound when purchased in 

 bulk. Quite a number of other arsenicals have been more or 

 less used as insecticides and some of these are of considerable 

 value while others have no especial advantages over Paris green 

 or arsenate of lead, or are decidedly inferior. 



London purple was formerly used in spraying. As sold in 

 the market its composition is unstable owing to its being apt 

 to be adulterated, and it is very caustic, hence liable to scorch 

 tender foliage. For these reasons it is rapidly going out of 

 use. As a spray it is applied in the same proportions as Paris 

 green, as is also arsenite of copper. 



Arsenite of copper (Scheele's green or "green arsenoid") is 

 of -similar composition to Paris green, and is even superior 

 owing to its more rapid effects and less liability to produce 

 scorching. It is, however, not as yet so readily obtainable. 



