It is only a step from the consideration of nutrition of a plant or
animal to that of medication. Remedial agents are readily introduced
into plants, either through the roots, or by spray on the foliage, or by
direct injection into the trees. Going a little further, such methods
become means of killing trees.
A few years ago, I became interested in killing trees in a way which
would prevent sprouting and also protect the wood to some extent from
insect attack and decay organisms. More recently my interest has turned
toward the use of hygroscopic chemicals injected in the living tree for
the purpose, not only of killing the tree, but of preventing the wood
from cracking radially or drying. A number of government
publications[4-10] have contributed information along this line.
To inject enough chemical to accomplish this purpose it seems necessary
to introduce the chemical solution through a cut the depth of the sap
wood and extending entirely around the tree. A collar of water-proof
paper cemented to the tree provides a means of supplying the chemical
solution to the cut. All this is described in the literature cited. The
only contribution I have made is the use of urea in the solutions.
Many salts are more soluble in a water solution of urea than in water
alone, and many such mixtures are very hygroscopic. Moreover, it seems
that in the presence of urea higher concentrations of salt may be
introduced into the sap stream of trees, though I do not as yet have
experimental data to confirm this statement quantitatively.
An example of a solution injected into a small ash tree is as follows: