The southeastern corner of the State has a higher percentage of
infection than any other portion of the State. The rapid increase of
the blight is well shown in this section by the record of 1,637 trees
on tracts in the vicinity of Philadelphia, which were examined for
blight in October and November, 1910, December, 1912, and August, 1913.
In 1910, 31 per cent. of these trees were infected with the blight, and
29 per cent. were doubtful. In 1912, 79 per cent. were infected, and in
1913, 88 per cent. If we include the 29 per cent. doubtful trees with
the 31 per cent. certainly infected in 1910, the total becomes 60 per
cent. This makes the annual increase in infection approximate 10 per
cent. per annum. In this connection it is interesting to note that on
the du Pont estate at Kennett Square, Pa., where tree surgery methods,
supplemented by spraying with Bordeaux mixture, have been in use for
the past two years, the progress of the blight has been materially
delayed. Mr. R. E. Wheeler, forester for the estate, believes that
these methods will save the trees under treatment for at least five
years more, and probably for a much longer time.
[Illustration: Figure 2.
Cross section of the Blue Ridge Mountain, showing altitudinal
distribution of the chestnut blight on north and south slopes]
Tree surgery without spraying has had little effect in delaying the
progress of the blight after it attacks a tree. In a large orchard
of Paragon chestnuts, in Northumberland County, in a block of 9,612
trees, 4 to 15 years old, thoroughly examined in the winter of 1911-12,
194 infected trees were found, (2 per cent. infection), 103 of which
were so badly diseased that they were cut out and burned, and 91 trees
were treated by surgical methods. In the winter of 1912-1913, this
same block was again carefully gone over, and 1,064 infected trees
were found, (11.2 per cent. infection), 325 of which were marked for
removal, and the balance for surgical treatment. The rate of increase
in this case was over 500 per cent.