THE TREATMENT OF INSECTS AND FUNGI IN THE UNITED STATES. 208 



recommended below, which is intended to suit the average con- 

 dition. The proportions are : Three ounces of soap in three pints 

 of water or sour milk, and three quarts of kerosene for ten gallons 

 of emulsion for scale insects, or for fifteen gallons for plant lice. 

 Another formula, which is easier made but more expensive, and 

 so only recommended for use on a small scale, consists of using 

 eight times as much soap. When so made the creamy mixture 

 described above, obtained within five minutes, is a permanent 

 emulsion. 



Paris Green and London Purple. — These poisons kill only 

 those insects that eat the leaves covered by them, and are useless 

 against sucking insects like plant lice and scales. They are also 

 useless against overwhelming numbers of insects, such as 

 swarms of grasshoppers, which are able to eat up the plant 

 before getting poison enough to kill them. Arsenic is the active 

 principle in both these poisons, and is about equally strong in 

 both. Paris green is copper arsenite, and London purple an 

 arsenite of lime containing an aniline residue, to which the 

 purple colour is due. The latter is a finer powder and remains 

 better suspended in water, but the Paris green is, as a rule, safer 

 to apply. Both poisons, if applied too strong, will burn the 

 foliage, and both require constant stirring or the material will 

 settle to the bottom, and so not be uniformly distributed. For 

 the best results the poison should not be allowed to drip from 

 the tree, and the finer the spray the better. These poisons do 

 not as a rule remain any great length of time on the plant, but 

 must be renewed every two or three weeks, or while the danger of 

 insect attack exists. In mixing the poison it is well to first 

 make a paste with a little water and then dilute, as otherwise it 

 is difficult to wet the leaves with it. The amount used is about 

 1 lb. to 200 gallons of water * 



The following table is intended to give, at a glance and in a 

 small compass, the ingredients, proportions, and method of pre- 

 paration of various washes. For convenience they are calculated 

 in per cents, for metric calculations, while the amounts necessary 

 for five and forty gallons respectively (as representing an oil-can 

 and barrel) are given in the common weights and measures. 



* In England 1 oz. to 20 gallons of water is sufficient. We have 

 known trees seriously damaged by the application of 1 oz. to 10 gallons. 

 N.B. — Trees should never be sprayed whilst in bloom. — Ed. 



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