PARK AND CEMETERY. 
276 
PREVENTION AND CONTROL OF TREE DISEASES 
Extract from address before the Massachusetts Horti- 
cultural Society by Dr. Haven Metcalf, Washington, D. C. 
The principle of conservation of forests 
has been so thoroughly discussed, and at 
least the major lines of activity for the 
next few years so thoroughly laid out, 
that this question needs no discussion even 
by way of introduction. Under American 
conditions the most important feature in 
the care of forests is forest protection, and 
this subject falls mainly into three divi- 
sions : protection against fire, against insects, 
and against fungous and other diseases. 
If we extend our survey beyond the living 
forest and take into account the decay of 
timber, due probably wholly to fungi (al- 
though the role of bacteria in this regard 
is practically uninvestigated) we see that 
we have an enormous field of investiga- 
tion and that the activity of fungi is in 
the long run responsible for the deteriora- 
tion of more property than the forest fire 
itself. The preservative treatment of tim- 
ber as it is being evolved in commercial 
hands and under the leadership of such 
an organization as the Forest Products 
Laboratory, maintained by the United 
States Forest Service at Madison, Wis., 
is solving the problem of the control of 
timber decay in a practical way. The path- 
ological aspects of this work are of great 
interest, and they are being made the sub- 
ject of continuous investigation. 
In forest pathology we have to deal with 
trees under two cultural types : first, the 
trees in the forest; second, shade, orna- 
mental, and park trees. When we come 
to consider the question of commercial con- 
trol, which from my viewpoint is the prin- 
cipal aim and end of forest pathology, we 
see that we have two very different lines 
of attack, conditioned entirely by commer- 
cial considerations. A shade or ornamental 
tree has great individual value. It is under 
constant observation, or should be, and we 
can employ in the prevention of disease 
the methods of control that have been 
evolved with such remarkable success in 
the control of orchard-tree diseases. In 
other words, we can spray, we can adopt 
elaborate systems of pruning and wood 
surgery, we can follow such quarantine 
methods as are now used in the control of 
pear blight and other diseases in the Pacific 
states. Along these same lines forest 
pathology may be expected to evolve to- 
gether with pathology of fruit trees and 
general refinements of the practice of hor- 
ticulture. 
When we consider diseases of the forest, 
however, commercial conditions are quite 
different. It is not possible to give the in- 
dividual tree any consderable attention. 
W e must consider the forest en masse. 
This being the case, it is apparent that 
there is indicated for forest pathology a 
line of evolution quite distinct from that 
which characterizes the applications of 
pathology in horticultural practice ; and for 
the present I may say that this develop- 
ment will be along the line of what a 
physician would call “preventive medi- 
cine,'’ as is the case in animal or human 
disease when we are considering the species 
en masse. Unquestionably the prevention 
of disease, rather than the cure, is the im- 
portant thing in any branch of plant pathol- 
ogy. The elaborate treatment of hollow 
trees, constituting a part of what is at 
present known as tree surgery and which 
has been built up on a wholly empirical 
basis, must give way in a few years to a 
more sane and simple preventive horticul- 
tural practice. The time to treat sap-rot 
or heart-rot in a tree is not after the 
heartwood or sapwood is rotted and the tree 
has become hollow, but years before, when 
the bark has just been torn off, perhaps 
by the teeth of a horse, and two or three 
square inches of wood are exposed. It is 
the man who goes over his young shade 
trees at least once a year with his dish of 
coal-tar who at the end of twenty or fifty 
years will have trees that require no heavy 
bill for tree surgery. 
So far as this country is concerned, for- 
est pathology is the newest branch of 
plant pathology. During the past few years 
we have made in the Department of Agri- 
culture a disease survey of the national 
forests. Many fungi, such as Echinodon- 
tium tinctorium or Polyporus amarus, 
which five years ago were mere myco- 
logical curiosities or wholly unknown, have 
been discovered to be serious enemies of 
forest trees. I may now briefly indicate the 
lines of attack upon some of these forest 
diseases, and first I may speak of the dis- 
eases of reproduction. 
When a tree reproduces itself naturally 
in the forest the great majority of young 
seedlings perish before they have “passed 
the kid’s lip, the stag’s antler.” It is 
therefore necessary that in large reforesta- 
tion operations the young trees be started 
in nurseries, and so there has been built 
up a large forest nursery practice, private, 
state and national, which every year is 
enormously increasing. Now every per- 
son present who has attempted to grow 
even a few forest tree seedlings, particu- 
larly conifers, knows how they suffer from 
damping-off and related diseases of in- 
fancy. We have set ourselves to no less 
a task than the overcoming of these damp- 
ing-off diseases by the use of soil fungi- 
cides, and have so far met with very good 
success. If damping-off and related nur- 
sery diseases can be overcome in a prac- 
tical way, one of the greatest factors in 
the way of artificial reforestation will be 
removed. This problem is so closely re- 
lated to soil and weather conditions that 
it will probably have to be worked out 
variously for different sections of the coun- 
try. For conifer seedlings sulphuric acid 
is the most hopeful soil fungicide, accord- 
ing to the researches of Spaulding and 
Hartley. This has the advantage of kill- 
ing weeds and stimulating germination of 
the conifer seeds, in addition to preventing 
damping-off. It has been successfully ap- 
plied by Spaulding in New York and Ver- 
mont, and by Hartley in the sand-hill 
section of Nebraska; it is yet to be tested 
in other parts of the country, Another 
destructive disease “blight” affecting year- 
lings or two-year-old conifer seedlings has 
in Nebraska and Colorado yielded readily 
to a modified system of watering and 
shading. 
Another disease which is essentially a re- 
production disease is the white-pine blister 
rust. Trees that are affected with this 
disease rarely survive the twentieth year 
and the greatest loss comes in the nursery. 
This disease is not indigenous to America, 
but has been introduced within the past 
ten years in nursery stock imported from 
Europe. Just what this disease will do if 
allowed to gain a foothold in this country 
we do not know, and we cannot afford to 
take the risk of waiting to find out. A 
disease which effectively prevents the cul- 
tivation of white pine in three northern 
countries of Europe should not be permit- 
ted to gain a foothold in this country if 
we can help it. I believe I am safe in say- 
ing that at the present time the white-pine 
blister rust is under control. We know 
of no places in America where this disease 
now exists ; but there are many localities 
where it has been found that must remain 
under suspicion for years, and there must 
not be the least relaxation of vigilance in 
the attempt to stamp out this disease. For- 
tunately for us, the blister rust has been 
for fifty years the subject of serious study 
in Europe. The life history of the parasite 
was known and many of the biological re- 
lations of the disease ; hence the great facts 
regarding its control were perfectly un- 
derstood when it reached this country. The 
present control of this disease in America 
and its utimate eradication, if we can hope 
for this, furnish the justification, from the 
practical man’s standpoint, of fifty years’ 
scientific research on this disease in Eu- 
rope. Would that we were as fortunate 
in the case of the chestnut bark disease 
and other epidemic diseases, in having at 
our disposal the result of years of an- 
tecedent research ! 
In the control of such diseases as the 
