18 OUR SHADE TREES AND THEIR INSECT DEFOLIATORS. 



ing will accrue to the plant from the proportion of poison recommended. 

 The new growth, that developed after the first poisoning, was protected 

 by one-fourth of a pound to the barrel in 1882. From midsummer un- 

 til autumn the unpoisoned half of the grove remainded denuded of 

 foliage, while the poisoned half retained its verdure. The little damage 

 then appearing in the protected part was mostly done before the first 

 treatment. Eggs were laid abundantly throughout the season. Many 

 of these seemed unhealthy and failed to develop, probably because they 

 were poisoned. Many hatched, but the young larvae soon died. The 

 eggs were seldom deposited on the young leaves that were appearing 

 after the poison was applied, but were attached to the developed leaves, 

 and here the larvre generally got the poison to prevent their attack 

 upon the aftergrowth. Still the young leaves became perforated to 

 some extent. The adults, which fly from tree to tree, appeared plenti 

 fully without much interruption throughout the season, and often several 

 could be seen feeding on each tree. Possibly many of these may have 

 become poisoued before depositing the eggs. 



The efficiency of London purple being established, it will generally 

 be preferred to other arsenicals, because of its cheapness, better diff'us- 

 ibility, visibility on the foliage, &c. As the effects of the poisons com- 

 monly do not appear decidedly for two or three days after their admin- 

 istration, the importance of the preventive method of poisoning in 

 advance cannot be too strongly urged. As the effect is slow in appear- 

 ing, impatient parties will be apt to repoison on the second or third day, 

 and thus put on enough to hurt the plant when the effect does come. 

 Much depends on dryness or wetness of the weather; but good effects 

 may be expected by the third or fourth day. 



London purple seems to injure the plant less than Paris green. 



Treatment with Paris gree/i. — In 1883 the Paris green was first applied 

 on the 29th of May, at which date the eggs were extremely abundaut 

 and hatching rapidly on the leaves. Paris green, flour, and water were 

 mixed by the means previously employed with London purple and 

 already described. The mixture was applied to the north part of the 

 same grove of elms. Thus far experience shows that the Paris green 

 is effective against the insect, but that this poison injures the plant more 

 than does the Loudon purple. 



Three fourths of a pound of Paris green to a barrel (3G or 40 gallons) 

 of water, with 3 quarts of flour, may be regarded as a poison mixture 

 of medium or average strength for treating elms against these beetles^ 

 and the indications thus far are that the amount of Paris green should 

 not be increased above one pound or be diminished much below one- 

 half a pound in this mixture. To a bucketful of water three-fourths of 

 an ounce of Paris greeu may be used. The action of this poison is 

 slow but severe, and varies much with the weather. Thus far the re 

 suits of tests have been varied so much by the weather and different 

 modes of preparation and application that they will be repeated. When 



