Results of spraying experiments against caterpillars of the gypsy and brown-tail moths

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MASSACHUSETTS SOCIETY FOR PROMOTING
AGRICULTURE.

RESULTS OF
SPRAYING EXPERIMENTS

AGAINST

CATERPILLARS OF THE GYPSY

AND BROWN-TAIL

MOTHS

May, 1905

See last page of the cover

MASSACHUSETTS SOCIETY FOR PROMOTING
AGRICULTURE.

RESULTS OF
SPRAYING EXPERIMENTS

AGAINST

CATERPILLARS OF THE GYPSY

AND BROWN-TAIL

MOTHS

May, 190^

See last page of the cover

ARNOLD ARBORETUM, HARVARD UNIVERSITY.

Jamaica Plain, Mass., June 8, 1905.

To THE Trustees of the Massachusetts Society for

Promoting Agriculture :

Dear Sirs : — Your committee appointed to consider
methods for the suppression of the gypsy and browntail
moths in Massachusetts make the following report:

The possibility of killing these moths by poisoning the
foliage of the plants on which they feed not having, it
appeared, been fully recognized in this State, your Commit-
tee arranged in May for a public exhibition of this meth-
od of insect destruction on a scale large enouo-h to be con-
elusive.

The trial was made on May 22nd and continued through
four days, and on May 31st and June 1st was supple-
mented by an additional application of poison to prevent
invasion from unsprayed woods and trees in the neighbor-
hood. The work was done under the direction of Mr. J.
A. Pettigrew, Superintendent of the Boston Park System,
whose report on the details of the work with its cost is
appended.

The piece of land in Melrose selected for the experi-
ment, 11. 4 acres in extent (the area as given by the engi-
neers of the Metropolitan Park Commission), was covered
with a growth of White Pines, Oaks, Beeches, Apple-
trees, Willows and Hop Hornbeams, and with a dense
undergrowth of Alders, Sumachs, Barberries, Witch
Hazel and seedling trees of several species. All the trees
were badly infested with the nests of the browntail moth
and the egg-clusters of the gypsy moth, and old walls and

piles of stone gave safe and convenient shelter for egg-
clusters. No work of suppression of any sort had been
attempted on this land which appeared to your Committee
to be as badly infested as any piece of land of similar size
that could be found in the state.

The difficulty and expense of thoroughly poisoning the
foliage on this particular piece of land was increased by
the thick growth of trees and shrubs and by the unusual
height of many of the trees. Several Pines and Elms ex-
ceed a height of seventy to eighty feet, and could be
covered with poison only by the use of a forty to sixty
foot ladder, the average size of all the trees being proba-
bly much above that of the forest growth in the infested
region. Spraying operations were simplified by the fact
that every part of the land could be reached by hose from
the pump stationed on a highroad, and by the convenient
access to water. Setting the height of the trees, their
number and the dense undergrowth against the exception-
able facilities for operating the pump and obtaining a
supply of water, the cost of the first four days' work
(-121.87 per acre), exclusive of the cost of the machine
and hose, can perhaps be safely taken as a fair average
cost per acre of thoroughly spraying woods in any
part of the infested region. More powerful machinery,
better adapted to spraying on a large scale, and some cheap-
er form of poison may, however, be expected to reduce
the cost of the operation.

A careful inspection of the sprayed area made on June
7th showed that the foliage had not been destroyed. Only
a few half-dead caterpillars, too feeble to be dangerous and
soon to die, could be found on the leaves, while piles of
dead caterpillars on the ground showed the effect of the

poison. Trees in the neighborhood that had not been
sprayed, and on which no work of suppression had been
done, were on June 7th entirely denuded of leaves. So
far therefore as killing the caterpillars on this piece of
ground is concerned the experiment has been entirely suc-
cessful. It shows: —

First, that it is practicable to apply poison to the foli-
age of trees crowded in woods in sufficient quantities to
insure the death of all insects feeding on it ; and that it is
not necessary to try other means of destruction if the
spraying is done effectively and at the right time.

Second, that this method of destruction of the gypsy
and browntail moths is cheaper and more effective than
any of the methods which have been in general use for
the destruction of these insects.

Third, that this method makes possible the preservation
of the young trees and shrubs neccessary for the perpetu-
ation and beauty of the forest, previous attempts to de-
stroy the gypsy moth on trees growing in woods being
dependent on the destruction of all small plants able to
afford them shelter and retreat.

Of the possibility of the easy destruction of the caterpil-
lars of the browntail moth by arsenical poison when they are
fully grown in spring or in September when they are first
hatched there is no question. Our experiment has shown
that it is practicable to kill by arsenical poison the caterpil-
ars of the gypsy moth when they are first hatched, but it is
still to be demonstrated that poisoning is effective against
the full grown caterpillar, and it is evident that the mature
caterpillars entering a sprayed territory will not be killed
by poison applied six weeks earlier to trees which have
produced new leaves since the application was made.

5

Spraying, to be really effective, must be general, or, if it
is not general, sprayed ground must be protected from in-
vasion by some mechanical device.

Of the value of spraying against these insects on iso-
lated street or orchard trees there can be no question.
For such trees no matter what their size may be, it is ef-
fective and cheap. A comparison now of some of the
large Elm trees on the sprayed territory on Wyoming
Avenue with the Elm trees of similar size on many streets
of the infested district will show the value of arsenical
poison. In many cases these street trees have been care-
fully and laboriously cleared of egg-clusters and nests, but
the impossibility of getting the last cluster or the last nest
is shown by the presence on these trees of enough cater-
pillars to defoliate them. The impossibility of destroying
all the egg-clusters of the gypsy moth in any given locality
is well shown, too, at this time in the Middlesex Fells
where thousands of the caterpillars can be seen on trees
in regions from which all undergrowth has been removed
and where it was believed every egg-cluster had been
killed.

C. S. Sargent, i

John Lowell, V Committee.

H. S. HUNNEWELL, )

Boston, June 6, 1905.

Professor Charles S. Sargent, President,

Mass. Society for Promoting Agriculture,
Dear Sir:

Agreeably to your request that I take charge of an ex-
periment proposed by your Society for the suppression of
the gypsy and brown-tail moths, by spraying the foliage

6

attacked by them with an arsenical solution, I arranged for
the mounting of a Worthington steam pump, of 35 gallons
per minute capacity, on the frame of a portable steam boil-
er of 8 horse power, the whole costing !$485.00 which at-
tached to an ordinary 600igallon street sprinkler, made an
apparatus capable, under a pressure of 120 lbs. per square
inch in the pump chambers of projecting two streams from
• 3/16 inch diameter nozzles to a height of fifty to sixty feet.
Another stream conducted through a perforated pipe into
the sprinkling tub served as an agitator for the poisonous
solution used. 200 feet of 1 1/2 inch diameter hose was
used as a main supply for the two distributing hose, which
were each 200 feet in length, the first 100 feet being of one
inch diameter while the second 100 feet of each was 3/4 of
an inch in diameter, on the ends of which were the nozzles.
An additional street sprinkler of 600 gallons capacity
was used as an alternate to keep the pump in constant use.
A single horse supply wagon, three sets of 40-foot exten-
sion ladders, and a corps of eight men, one foremen, two
teamsters, and an engineer completed the equipment.

The piece of woodland selected by you was located at
the junction of Ravine Road and Wyoming Avenue, adjoin-
ing the Middlesex Fells Reservation, being entirely bound-
ed by these roads and containing 11.4 acres. It is filled
with a heavy and tall growth of pines and deciduous trees,
which were badly infested with gypsy and brown-tail
moths.

When the work of spraying commenced, on May 22,
the gypsy larvae were about 3/8 of an inch long, and
the brown tail larvae about 5/8 to 1 inch long. The
spraying was completed in four days. Subsequently, a
lighter gasoline machine of three and one-half horse power,

and four men were employed for 4 days from May 31 in
adding a second coat of the solution, at the edge of the
woodland to a depth of fifty or seventy-five feet, to meet
the present invasion of brown-tail larvae from the woods
across the boundery roads, and of the gypsy larvae later.

Disparene, a composition of arsenate of soda and ace-
tate of lead, was used in the proportion of ten pounds of
the solution to one hundred gallons of water. At least
two-thirds of the area had to be sprayed from ladders, on
account of the height of the trees about 160 of them being
60 feet high and upwards. When conditions were favor-
able, foliage seventy-five feet distant laterally could be cov-
ered with fine spray. To make the solution more adhesive to
the foliage, flour, molasses, and glucose were each tried in
turn, being mixed with the solution : the result in each
case was satisfactory.

The net cost of first spraying was $249.09, or at
the rate of $21.87 per acre. With the supplemental
spraying of the borders included, the net cost was 1338.04,
or 1)29.65 per acre. The total cost of the work was $394.34.
This includes cost of transport of equipment to and fro,
and for time lost by men working so far from home, which
is deducted as not being a legitimate charge in the cost of
the work.

The poison was found to be effective against the gypsy
larvae on the second day, many being dead, others appear-
ing sick and'^ torpid. In a week the effect was much more
noticeable, the larger and stronger brown-tail larvae being
also similarly affected, while nearly all of the larvae of the
gypsy moth were dead.

Very Respectfully submitted,

J. W. Pettigrew.

BROWN-TAIL MOTHS.

March 18th. The caterpillars begin to leave nests, and
commence eating.

June 10th. Commence to spin cocoons and pupate.

July 1st. The white moths, with a brown tail, commence
to emerge from the pupal stage, and soon begin to lay
eggs. The eggs hatch in from 15 to 20 days.

July 20th. They begin to feed about this time, and feed
for about six weeks.

Sept. 1st. The)' liegin to form their winter nests.

GYPSY MOTHS.

April 30th. Egg-clusters commence to hatch, and cater-
pillars begin to feed about this time.

July 15th. They commence to pupate about this time.

July 25th. The moths commence to appear, and soon
commence laying egg-clusters.