J 06 STATE HORTICULTURAL SOCIETY. 



are, which one of the arsenites shall wo use? How strong shall we nso it? 

 And when shall we apply it to be most effective and yet produce the least 

 injury to the foliage? I was sorry to learn, yesterday, in conversation, 

 that many are advocating the use of white arsenic. Don't do it. Don't 

 use it yourself nor advise others to iise it. It is more dangerous to handle 

 than London purple or Paris green, and is more injurious to the foliage. 

 To be sure, it is the arsenious acid in London piirple and Paris green that 

 makes them valuable as insecticides, and we may say that, this being so, 

 we will buy white arsenic and thus know what we are getting and how 

 strong it is. The truth is, however, that we will be no more certain of 

 getting a uniformly strong article than were we to buy London purple or 

 Paris green, for all can be adulterated equally well. Besides, relative 

 strength is not the only consideration. Relative effect on foliage is far 

 more important. The arsenious acid in Paris green is in combination with 

 copper and is very insoluble, only about one part being soluble in twenty- 

 five thousand parts of water. The proportion of soluble arsenious acid in 

 London purple seems to be somewhat greater. Both London purple and 

 Paris green remain in suspension in water, and if thrown upon foliage in 

 moderate (juantities produce but little, if any, injury under ordinary 

 circumstances. If a heavy rain follows soon after spraying, however, the 

 ammonia in the rain water probably renders the arsenious acid more 

 soluble. It is dissolved, enters the tissue of the leaf, and the foliage is 

 'burnt.' White arsenic, being more soluble, does not need the aid of rain 

 in its destructive work. Spray it upon a tree, in I don't care how weak a 

 solution, provided it is strong enough to kill the curculio, and I am sure 

 the foliage will suffer. Paris green is preferable to Loudon purple for the 

 same reason that the latter is preferable to arsenic — /. c, less of the 

 arsenious acid is soluble. 



AS TO STRENGTH OF SOLUTION. 



"The question in regard to how weak a solution we can use and still be 

 effective, is more difficult to answer. Until last season we have experi- 

 enced but little injury from using one pound of London purple to one 

 hundred gallons of water, and tliat is certainly effective. Eesults all over 

 the state the past season, however, show that we can not safely use so 

 strong a mixture. We sprayed both cherry and plum trees, at various 

 times, from May 20 to June 12, with London purple, the strength of the 

 mixture varying from one pound to one hundred gallons of water to one 

 pound to two hundred gallons, and the foliage was injured but very 

 slightly, if at all. June 24, we sprayed peach, apple, and plum trees with 

 one pound of London purple to one hundred gallons of water. Pain 

 followed the next day and the injury was very great. From July 5, to July 

 10, we sprayed peach, pear, and cherry trees with one pound of London 

 purple to two hundred gallons of water. In every case the foliage on the 

 peach trees was badly injured. Jiily 11 we sprayed peach trees with Paris 

 green. We used one pound to one hundred, to two hundred, to two hun- 

 dred and fifty, and to three hundred gallons of water. In the first propor- 

 tion the injury to the foliage was slight. In the others none at all. From 

 these experiments it appears, first, that London purple is much more injur- 

 ious to foliage than is Paris green; second, that peach foliage is much 

 more susceptible to injury than is that of the apple, plum, pear, or cherry; 

 third, that we may spray apple, phim, pear, and cherry trees with London 



