56 BUULiETIN 816, U. S. DEPAETMEISTT OF AGRICULTURE. 



Because of the height which many street trees attain a powerful 

 outfit is required to spray them properly. One capable of maintain- 

 ing a pressure of 200 pounds per square inch is desirable. The type 

 of spray required for tall trees is different from that used on fruit 

 trees and other low plants. For low trees the ideal spray is a mist 

 within a few feet of the nozzle, application being accomplished by 

 having the nozzles near the foliage to be treated. For tall trees it is 

 desirable that the liquid should leave the nozzle in a solid stream, 

 which is broken into spray as it passes through the air. The material 

 has to be projected with sufficient force to reach the highest trees 

 before being entirely converted into mist, as it is impracticable to 

 extend the nozzles into the trees to reach the farthest portions, as is 

 done with fruit and other low trees. The spray can not be applied 

 as uniformly as a mist, but it is impracticable to climb into the 

 tops of shade trees to cover every part with a cloudlike spray. On 

 the other hand, the mist spray is better for small trees, as much 

 injury may be done to low trees or to the lower branches of high trees 

 by the force of the stream from high-pressure outfits. 



It is estimated that in practice up to 95 per cent of the attacking 

 insects can be killed with insecticides carefully applied by the stream 

 method under high pressure. 



In addition to the mechanical problem of satisfactorily covering 

 high trees with insecticides or, fungicides there is the problem of 

 selecting materials that will be effective against the insects and dis- 

 eases and at the same time will not disfigure the paint or stone work 

 of adjacent buildings with which the materials must inevitably 

 come in contact in street-tree spraying. It frequently happens that 

 the most effective remedies must be rejected because of the damage 

 they would do to buildings and that less efficient materials must be 

 used. 



Whitewashing the trunks of trees is a useless and unsightly prac- 

 tice — useless, as it does not prevent the attacks of insects, and 

 unsightly, because it makes the trunks of the trees obtrusive when 

 they should be inconspicuous. 



Banding with cotton or proprietary preparations may occasionally 

 be useful, but because such applications are so seldom helpful and 

 because some of the preparations result in injury due to constriction 

 of the trunks, it should not be resorted to except upon special 

 recommendation of an entomologist familiar with the existing 

 conditions. 



Details as to enemies to be expected, methods of treatment, and 

 materials to be used may be found in other publications ^ or may be 

 obtained by correspondence with the nearest State agricultural experi- 

 ment station or with the United States Department of Agriculture. 



1 See list on following pages. 



