Insects of Shade Trees and Their Control. 15 
whenever it is found cracking or breaking away from the wound. A 
pure white-lead and linseed-oil paint is sometimes employed for tree 
wounds, and, while not as satisfactory as the coal-tar-creosote paint, 
it is a good deal better than nothing. Ordinary grafting wax will 
give good results for small surfaces. 
FILLING TREE CAVITIES.’ 
Decayed scars and cavities in the trunk or limbs are frequently 
infested with wood-boring larve or are the retreat of different species 
of ants. Such cavities are objectionable, for not only do they favor 
gradual decay and weakening of the trees, but they afford an ex- 
cellent winter harbor for certain injurious insects. As noted else- 
where (p. 16), cavities in the trunk usually are the result of improper 
pruning and neglect to care for wounds from other causes. Such 
cavities may be filled with cement and the condition of the trees 
materially improved. 
The first operation is to remove all of the decayed wood, and this 
_can be done by means of a gouge, chisel, mallet, and knife. In cut- 
ting around the edge of the cavity nothing but very sharp tools 
should be employed, as dull instruments wili injure the cambium. 
As soon as the cambium has been cut to a proper distance it should 
be covered with a coat of shellac. After the cavity has been 
thoroughly cleaned out it should be treated with creosote and coal 
tar, as described under the preceding heading, and it is then ready 
to receive the permanent filling.* 
PRUNING AS RELATED TO INSECT INJURY.* 
Certain twigs and branches, when heavily infested with or in- 
jured by insects, frequently can be removed to best advantage in the 
course of pruning operations. Also, in the work of pruning, thought 
should always be given to maintaining the shape of the trees to 
facilitate the application of sprays. 
In case of severe insect injury, large trees may sometimes be 
severely cut back or “dehorned” to advantage. With old trees, 
however, too much wood should not be removed at one time, and the 
dehorning process should be extended over two or three years. Small 
limbs and twigs incrusted with scale insects or punctured by the 
periodical cicada, or tree-hoppers, ete., usually may be removed to 
advantage. Pruning should be done preferably before the ap- 
plication of dormant tree sprays, since it is a waste to use spray 
materials on limbs and branches that are to be removed later. 
2 Adapted from Farmers’ Bulletin 908. 
’Por full information on this subject, see ‘‘ Tree Surgery’ by J. F. Collins, Farmers’ 
Bulletin 1178, U. S. Department cf Agriculture. 
4 Adapted from Farmers’ Bulletin 908. The general subject of pruning shade trees is 
od 
discussed in Bulletin 816, U. S. Department of Agriculture, and in Farmers’ Bulletin 1178. 
