56 BULLETIN 816, U. S. DEPARTMENT 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 familar 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. 
