There are many points to be observed in removing diseased trees in spot
infections, if the disease is to be permanently wiped out. The main
point to keep in mind is the fact that the fungus propagates itself
more readily as a saprophyte than as a parasite, so that unpeeled logs,
strips of healthy bark and chips from diseased trees or nearby healthy
ones, if left in the woods, are almost certain to become infected. The
principal object is to do the work in a thoroughly sanitary manner at a
reasonable cost. An experienced man acquired “tricks of the trade” that
enabled him to do the work much more thoroughly and in less time than
an inexperienced hand can do even a poor job. Great care was necessary
in supervising the work of removal carried on by the individual owners,
since each spot infection practically meant training a new man to do
the work, and unless an experienced man was constantly on the spot,
the work would seldom be done properly. On State forest reserves and
in cases of forced removals, the work was done by employees of the
Commission, and it was found that it was done at less cost and much
more effectively than was usually the case elsewhere.
The removal of an infected tree is best done as follows: First: Where
the ground beneath the tree is covered with a dense growth of brush,
this growth should be cleared away so that the chips and branches may
be easily picked up. Small chestnut or chinquapin trees or sprouts
should be cut flush with the surface of the ground and the tops burned.
The stump should be made as low as possible. The bark should be first
removed from the lower 3 or 4 feet of the trunk to an inch or more
below the surface of the soil. If felled by sawing, peeling may be done
after the tree has been cut down. During the fall and winter the bark
is difficult to remove, and if the stumps are cut low, it is easier and
cheaper to split off the sap wood and attached bark with an axe. In any
case the stump and all exposed roots must be cleared of every particle
of bark, and all bark removed must be carefully collected and burned.
[Illustration: Peeling blight infected trees in a spot infection.]
[Illustration: Figure 4.
Typical small spot infection, near Dry Run, Franklin County, Pa.,
showing original center and secondary infected trees. If all chestnut
trees within 35 feet of the nearest diseased tree cut in 1911 had been
removed at the time of the first cutting, and all stumps properly
sterilized, it would have prevented the appearance of the new
infections of 1912 and 1913.]
After the tree is felled, all portions above the stump which show
mycelium or pustules of the blight must be peeled of bark or the entire
piece cut out. This diseased material, the brush from the tops, the
bark, and portions of the felled chestnut trees which are not peeled
and which it is not intended to utilize must be burned.
After the stump is peeled, if fire can be made over it without injuring
the surrounding trees, and without danger of forest fires, the brush
and refuse is best piled over the stump and burned. The fire must
entirely consume or deeply char all of the material; no uncharred ends
of branches and small twigs can be allowed to remain without grave
chances of reinfection. If it is impossible to make the fire over the
stump without injuring the surrounding trees, the sides and top of the
stump and exposed roots should be thoroughly coated with creosote.
Portions of infected trees which show no evidence of the blight should
not be permitted to lie unpeeled in the woods over twenty days, but may
be safely handled and shipped with the bark on, if shipped as soon as
cut. If the logs from the diseased trees are not removed from the woods
within twenty days from the time the trees are felled, they should be
peeled and the bark burned, or else the entire trees burned. Wood from
diseased trees to be used where exposed to the weather must be peeled,
or the fruiting bodies are almost sure to appear on the dead bark and
become a source of infection. Fire wood, if kept under dry cover, need
not be peeled.
One of the most important time saving items is to peel the lower
portion of the tree before felling, and it is still more important to
cut the stumps as low as possible. Bark remaining between buttresses
and deep crevices of stumps can be removed very readily by chipping
down from a position directly over the low stump, which is not possible
in the case of high stumps. A rake and a large coal-burner’s basket
included among the tools used in burning, are very useful in cleaning
the chips from the ground. Before starting the fire, all the leaves
and debris for a considerable distance around the place where the
material is to be burned should be raked into a pile on which the fire
is started. The bark and small particles of wood are raked together
as soon as the brush is piled, instead of waiting until all the tops
are burned. In this way, no large quantity of leaves and fine rakings
are left until the end to smoulder for a great length of time before
burning, and thus increase the danger of forest fire.
All possible care should be taken to prevent injury to surrounding
chestnut trees and sprouts in felling the infected trees. Observation
has shown that nearby trees are too frequently injured through
carelessness, and the wounds are very apt to be a point of reinfection.
Experience has also shown that unbarked stumps of blighted trees and
green tops which are permitted to lie for a month or two on the ground
are almost certain to become infected. The spores germinate on the
sappy surface of the stump, and the mycelium grows downward through
the cambium, and in the course of a year or two reaches the sprouts
which come up around the base of the stump. In the case of the tops
and particles of bark and wood, the decaying bark appears to be a very
favorable seed-bed for the development of the spores that reach any
portion of this material. It must be impressed on the workmen that the
stumps must be peeled clean, and every particle of the diseased tree
must be either burned or utilized in such manner that no opportunity is
given for the saprophytic growth of the fungus.
It has been found that painting the thoroughly peeled stumps with
creosote is effective in keeping the stumps free from the pycnidia of
the blight fungus, but is not so desirable as hard burning over the
stumps. In an experimental cutting at Wildwood Park, Harrisburg, 55 per
cent. of burned stumps later showed blight, while only 23 per cent. of
the creosoted stumps showed any signs of it. However, it is possible
that in the future, many of the creosoted stumps will become diseased.
The results of an extensive experiment at Anderson Station, Mifflin
County, are given below. This experiment deals with the efficiency of
burning over stumps as compared with creosoting stumps. The stumps
in Table II were peeled at various times during January, February,
and March, 1913, and cold creosote applied with a brush. The cost of
creosote and labor of application was approximately one-fifth of a cent
for each six-inch stump, cut low. The data given below are the result
of an inspection of these stumps made December 12, 1913.
[Illustration:
Center of spot infection at St. Mary’s, Elk County, Pa. This tree was
infected at least four years prior to the time the picture was taken.]
[Illustration: A Spot Infection in Elk County, Pa.]