-1)1 Eei'ort of the Departmeint of Entomology of thq 



EFFECT OF THE GAS ON TREES. 



In the preliminary work on fumigation, in California, ospe- 

 daily of citrus trees, all injury to the leaves of the trees was 

 supposed to result from decomposition of tlie gas by sunlight 

 and heat. As a result fumigation is usually done at night in 

 that section, although it was found that by the use of black tents 

 the work could be done in the day time with less injury than 

 with uncolored tents. In the east the majority of the tests have 

 been made with black tents at a season of the year when the 

 trees were dormant, with the result that there was little or no 

 danger of injury from the conditions that orange growers have 

 to contend with. The principal injuries to deciduous trees 

 result from other causes, such as too heavy charges of chemi- 

 cals, over exposure or treatment after leaves have begun to 

 expand. 



In the following tables are shown some of the effects of difCer- 

 ent amounts of chemicals allowed to act for varying lengths of 

 time, together with notes on the same. In a study of these 

 tables the following notes will be of assistance: 



The chemical abbreviation KCN is used for potassium cyanide, 

 the chemically pure (approximately 98 per ct.) being used in all 

 cases. In most instances the maximum exposures were made 

 during the noon hour and comparatively few trees were treated 

 for long periods; in addition the number of trees receiving heavy 

 charges of KCN were small; hence the tables cannot be 

 averaged. 



The orchards in which the tests were made consisted of a 

 mixture in one case of apple, cherry, peach, pear and plum; in 

 the other of apple, cherry, chestnut, peach and walnut. In the 

 first, a small orchard, the trees were set haphazard; while in the 

 second, a peach orchard, the peach trees in every other row 

 alternated with apple, cherry, chestnut or walnut. No definite 

 order was followed in setting the alternating trees; and as a 

 result there were but few apples, walnuts, etc., and these were 

 often widely scattered. 



