Insecticides. 



23 



water, or 1 oz. to 6 — 15 gallons. The stronger mixtures may be 

 used when the plant has vigorous foliage, while the more 

 diluted mixtures should be employed when the foliage is 

 tender. For general purposes, such as spraying apple- 

 trees, 1 lb. to 150 gallons of water is a common average in 

 the United States. In Great Britain 1 lb. to 250 gallons of 

 water is found sufficient, with the addition of a little lime 

 and soft soap. The poison is first made into a thin paste 

 with a small quantity of water, and quicklime (in amount 

 equal to the poison) added, in order to lessen the danger of 

 scalding. The use of the lime is especially desirable in the 

 case of the tender-leaved plants, which are easily scalded, and 

 it is always better to use it with London purple. Paris green 

 is best used in Great Britain in the form of Blundell's paste. 



For leaf-feeding insects generally the spraying should be 

 done at the earliest indication of injury, and repeated as often 

 as necessary. In the case of the codling moth, usually com- 

 bated by this method in America, the first spraying is done 

 as soon as the blossoms fall, and is followed by a second 

 application a week later. This treatment is of little use in 

 this country, owing to there being a difference in the life 

 history here and in America. 



Care must be exercised in the use of arsenicals, as they are 

 very poisonous. American experience shows, however, that 

 if ordinary precautions are taken there is no danger attend- 

 ing their application. As regards their effect on the fruit, 

 the poison, generally speaking, disappears almost completely 

 from the plants in from 20 to 25 days (this depends largely 

 on the weather), and it is stated that, owing to the 

 great degree of dilution, the amount of ars3nic on any 

 single fruit, even shortly after the application, is so 

 small that impossible quantities would have to be consumed 

 to cause harm. Professor Riley has calculated, for instance, 

 that it would take several barrels of apples at a single sitting to 

 make a poisonous dose. Nevertheless, lo avoid all risk of 

 danger, plants should not be sprayed with arsenicals shortly 

 before the produce is ready to be eaten. It is also stated that 

 fruit trees should not be sprayed when in full bloom, on account 

 of the liability of poisoning honey bees or other insects useful 



