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Printed by Authority of the
STATE OF ILLINOIS

HENRY HORNER, Governor

DEPARTMENT OF REGISTRATION AND EDUCATION

JOHN J. HALLIHNAN, Director

The Peach Tree Borers
of Illinois ®

S. C. CHANDLER

NATURAL HISTORY SURVEY DIVISION

THEODORE H. FRISON, Chief

Circular 31 Urbana February 1939

STATE OF ILLINOIS
HENRY HoRNER, Governor
DEPARTMENT OF REGISTRATION AND EDUCATION

Joun J. HALLinAN, Director

BOARD OF NATURAL RESOURCES AND CONSERVATION
Joun J. HALLInAN, Chairman

WILLIAM TRELEASE, D.Sc., LL.D., Biology
Henry C. Cow.eEs, Ph.D., D.Sc., Forestry
L. R. Howson, B.S.C.E., C.E., Engineering

WitiiaM A. Noyes, Ph.D., LL.D.,
Chem.D., D.Sc., Chemistry
Epson S. BAsTIN, Ph.D., Geology

ARTHUR CuTTS WILLARD, D.Eng., LL.D.,
President of the University of Illinots

NATURAL HISTORY SURVEY DIVISION

Urbana, Illinois

SCIENTIFIC AND TECHNICAL STAFF
THEODORE H. Frison, Ph.D., Chief

SECTION OF ECONOMIC ENTOMOLOGY
W. P. Fuint, B.S., Chief Entomologist
Cc. C. Comrton, M.S., Associate Ento-

mologist

M. D. FarRAR, Ph.D., Research Ento-
mologist

J. H. Biccer, B.S., Associate Ento-
mologist

S. C. CHANDLER, B.S., Southern Field
Entomologist

L. H. SHropsuHirE, M.S., Northern Field
Entomologist

W. E. McCautey, M.S., Assistant
Entomologist

C. J. Weinman, M.A., Assistant Ento-
mologist

C. W. KEARNS, Ph.D., Research Fellow
in Entomology

Dwicut PowELL, M.S., Research Fellow
in Entomology

ArtTHUR E. RITCHER,
Fellow in Entomology

R. C. RENpDTORFF, B.S., Research Fellow
in Entomology

B.A., Research

SECTION OF INSECT SURVEY

H. H. Ross, Ph.D., Systematic Ento-
mologist

Cart O. Monr, Ph.D., Associate Ento-
mologist, Artist

B. D. Burks, Ph.D.,
mologist

G. T. RIEGEL, B.S., Assistant Entomolo-
gist

Assistant Ento-

SECTION OF AQUATIC BIOLOGY
Davip H. THompeson, Ph.D., Zoologist
GEORGE W. BENNETT, M.A., Limnologist
D. F. HANSEN, Ph.D., Assistant
Zoologist

SECTION OF GAME RESEARCH AND
MANAGEMENT

R. E. YEATTER, Ph.D., Game Specialist
C. T. Buack, M.S., Research Fellow

SECTION OF WILDLIFE
EXPERIMENTAL AREAS

A. S. Hawkins, M.S., Game Technician

F.C. BELLROSE; JR eos
Game Technician

Assistant

SECTION OF APPLIED BOTANY AND
PLANT PATHOLOGY

L. R. TeEnon, Ph.D., Botanist
J. C. Carter, Ph.D., Assistant Botanist
G. H. BoewE, M.S., Field Botanist

SECTION OF FORESTRY
James E. Davis, M.P., Extension For-
ester
LEE E. YEAGER, Ph.D., Forester

SECTION OF PUBLICATIONS
James S. Ayars, B.S., Editor

This paper is a contribution from the Section of Economic Entomology

(66787—4M—10-38)

<oeU,
cums 2
as

CONTENTS

ERE BEACH “BORER 5:6. cme sc elec i ee a ales I
Beach borer Life History Studies.........7...0....52... 1
MMO ule nTenremCeas 5.2 Giics aek bho sues oie sine Wlcs wie ae |
[eores iOMuOn MeiMGhAnCeS tt sae ec sens ow Oe le ee ee 3
Goumolor the Peach Borer... 2.222 65.0. iy. as eee be oe 4
Method of Treating for the Peach Borer.. Se ae
Injury from PDB Crystals and aenement ar Vows
Sipe GSrrartnse eet seat Seca ena toe vee Neh, Dat a 5
reno emoln ViOtiinGdGHiyas ie otk ee. te Oe oe 7
Amounts of PDB Crystals for Trees of Different Ages. 8
PiKieROle A PlCALION goat ti Aa Jae ele tees eek dc oe 9
CompaiaisonwOlSeasOMss 4.0 ys. asens cise i ae 10
BesteOatesworm spring Mreatments, 2.54. . 20.525. 10
Bes WanesmOneh alludbreatmentcmes ss. 2. eee ey
Prequency ok Ireatmente.......-. ere:
Removal of Grass and W aedks Before Taenianent See ey 15
SMOsiibtLessOnk Dau Cry Stale... oon 2. «60s pees. wees. 15
SOG! Sw OSHARERSS ngs Aa en eR Rac) WE ia aye 16
IPG OUINS Tb UUES Ry aniste hfe ary Woes oie ee te oie oo 16
SONG OurmMaMLiGguids=<*5.9 4 esa ee 10
Compansonvor-solids and Liquids. 2... 22.45.9255. .2* 21
Leroy Cite Rete Ry Sen ate ACN. 2s rte on ge nn Be, aA
Bitectiveness at, Low Temiperatures.............. 21
INGCESSILy Ore MOUmainge 6)... oa oe es OO
RGuipmicntaweauiredas a... becuase. Se acl: 24
fikitmerlineatnire cere. yok Scns a em ae ee a ce 2D
(CORTES) Ba NY 2 025 6 211 SS 9 gee ne ne es Ny nee ge 26
Summary of the Solid and Liquid Methods....... aA |
EE LESSER PEACH BORER... 2-6. soc eee: 28
PRPC HERO UBLED EL Vase ho Reet eee ae. eA Merah alos ae 29
DUseIET OVC ASUITES He: Soo Ae crs ttat cta Ais PS eae Bore OEE doe. 30
Bs eriimen tale WhO arn < aie il Ir ila Sac yas ee ak rly Sas 30
ManlerOh A nea ii Citra ve a tate se Stet sche ani cs delves hee 8 33

THE PEACH BARK BEETLE AND THE SHOT-HOLE

Peach borer, Conopia exitiosa (Say). The peach borer passes the winter as a worm

or larva, A, which, during the following spring and summer, feeds on the inner bark

of the tree. In summer it spins a cocoon, B (right), in which it changes to a pupa,

of which the skin is shown, B (left), and from which it emerges 18 to 30 days later

as a moth: C, male moth; D, female moth. The female moth lays eggs from which
larvae hatch. All figures four times natural size.

The PEACH TREE BORERS

of Illinois id S. C. CHANDLER

sidered the most important insect enemy of the peach tree

in Illinois. Although easily controlled, it is seldom eradi-
cated and in this state is found to some extent in all peach
orchards three years of age or older. Even orchards one and
two years old may become seriously infested.

? NHE peach borer, Conopia exitiosa (Say), is generally con-

Peach Borer Life History Studies

Peach borers pass the winter as whitish larvae, one-quarter
inch to slightly over an inch in length. These worms are usually
found most abundantly at the base of peach trees just below the
ground line, but they may be found as much as 10 inches above
or below this line. The presence of borers 1s indicated by masses
of gum, mixed with frass or sawdust, exuding from the tree
Erumkss te. 1.

During the spring and summer, the worms (frontispiece)
feed on the inner bark of the trees. They become full grown at
any time between the middle of June and the first of September.
They then spin cocoons of silk, incorporating in them bits of
frass. In these cocoons they change to the brown pupal stage
(frontispiece), emerging from 18 to 30 days later as clear-winged
moths (frontispiece).

The moths are in appearance similar to large wasps. The
average life of the moths is six days, during which time the
female, fig. 2, lays from 400 to 1,000 eggs. The eggs are placed
singly on or around the base of the trunks of peach and related
trees. In from 7 to 10 days, small white worms with brown
heads hatch from these eggs. The worms crawl over the outer
bark and, on finding a crack, they rapidly gnaw their way into
the inner bark. Here they continue to feed until cold weather.
There is but one brood a year.

Moth Emergence

Our life history studies have been concerned largely with
moth emergence because of its direct bearing upon proper
times of treatment for borers. For a period of six years, from

[1]

2 ILLINnoIs NATURAL HistoRY SURVEY CIRCULAR 31 February

1924 to 1929, inclusive, emergence records were kept in a num-
ber of orchards in the vicinity of Carbondale. During the early
part of this period, moth-tight cages were constructed around
the base of infested trees to catch the moths as they emerged.

>

Fig. 1.—Shown here at
the base of a tree is the
exudate (indicated by
knife) resulting from
peach borer attack.
Frass and gum at the
base of a peach tree
are indications that
peach borers are at
work or have been at
work on the inner bark.

Fig. 2.—Adult female
of the peach borer,
natural size, on white
arrow that points to the
exudate at the base of
the tree and the pupal
skin from which the
moth has emerged.
The average life of the
moth is six days, dur-
ing which the female
lays from 400 to 1,000
eggs. There is but one
brood each year; moths
emerge between late
June and early Oc-
tober.

Later, the daily emergence record was made by noting the
number of fresh pupal skins at each examination.

An examination of these data shows very little variation
from year to year, and it seems best to combine the data from
the six years, presenting them in the form of a graph. This
necessitates grouping the records. In fig. 3, graphically re-
cording emergence of peach borer moth from 1924 through 1929,
the records are shown in weekly periods, from the last week in
June until the middle of October. This graph shows emergence
starting late in June and ending October 10. In the period
covered by the graph, the peak was reached in the last week of

1939 CHANDLER: PEACH TREE BORERS 3

August. From the week ending August 22 to that ending Sep-
tember 19, 67 per cent of the emergence took place.

Location of Entrances

Another phase of our life history studies which has a
practical aspect relates to the amount of frass and exudation
visible without the removal of any soil from the base of the
tree. Growers frequently follow the practice of treating only
those trees that show gum and frass, commonly called borer
signs. The purpose of this jg
phase of our study was to
discover whether infestation
by peach borers could be
detected by superficial ex-
amination of the tree.

N
(eo)

Fig. 3—Graph illustrating composite
records of peach borer emergence in
orchards near Carbondale, 1924-29.
The records for the six years are com-
bined and shown in weekly periods.
Emergence is shown as starting late
in June and ending October 10; the
peak as being reached the last week
in August. The greater part of
emergence, 67 per cent, is shown
taking place between August 22 and
September 19. The recommenda-
tions contained in this circular for
control of peach borers are based

fo)
(eo)

h
(e)

8

iy)
[e)

NUMBER OF PEACH TREE BORER MOTHS EMERGING FROM IO TREES
Hn
(e}

upon these records because of the Ke
direct bearing of moth emergence
upon proper times of treatment for fo)
the borers. 254 Il 1825 1 8 15 2229 5 |2 19 26 3 10

JUNE JULY AUG. SEPT. OCT.
FOR WEEKS ENDING

In the fall of 1934, 50 trees, 10 in each of 5 orchards, which
at the surface of the soil showed no signs of borers, were examined
to determine the degree of infestation.

Of the 50 apparently uninfested trees, borers were found in
29. The borers, 107 in number, were distributed as follows:
First orchard, 48 borers divided among 10 trees; second orchard,
33 borers divided among 9 trees; third orchard, 2 borers divided
between 2 trees; fourth orchard, no borers in any of the 10
trees; fifth orchard, 24 borers divided among §& trees.

It is evident from this investigation that presence of borers
frequently cannot be detected by surface examination. How-
ever, we found that, in most trees harboring borers, removing

4 ILLinoris NATURAL History SURVEY CIRCULAR 31 February

an inch or less of soil would have revealed the presence of gum
and frass.

Control of the Peach Borer

Since the discovery in 1919 of the value of paradichloro-
benzene,* commonly called PDB, for the control of the peach
borer, much experimental work has been done by entomologists
of Illinois and other states and of the United States Bureau of
Entomology and Plant Quarantine on the many important
details of the operation known to the peach grower as gassing
the borer. In Illinois, control tests began in 1920, and almost
every year since some studies for the control of this insect have

Fig. 4.—Application of PDB for control of the peach borer. Left, the ring of PDB
around tree trunk on leveled ground. Right, the mound around the base of the
treated tree.

been made. From time to time some of the information gained
has been given out in the form of articles, state horticultural
society reports and unpublished talks at fruit growers’ meet-
ings. It is the purpose of this publication to summarize the
results of our peach borer studies and bring them up to date,
and to include information on the other borers of the peach
tree, the lesser peach borer, bark beetle and shot-hole borer.

Method of Treating for the Peach Borer

The commonly recommended method for gassing the peach
borer is as follows: Scrape earth from around the trees suffi-
ciently to allow spreading of the PDB crystals. Apply the
crystals in the form of a ring far enough from the trunk to
prevent their touching the bark (cover and fig. +). Use from

*As the name paradichlorobenzene (the chemical is sometimes called by growers ‘‘Painless Death
to Borers’’) is difficult to remember and pronounce, the abbreviation PBD has become common and
will be used hereafter in this publication.

1939 CHANDLER: PEACH TREE BORERS 5

one-fourth to one-half ounce PDB crystals on one- and two-
year trees; up to 2 ounces on large, old trees. Recommended
amounts for trees of various ages are given on page 8. Cover

Se
Pr «40

Fig. 5.—Left, peach tree with mound sufficiently large for PDB crystals. Right,
peach tree with mound needlessly large.

the PDB with four to six spadesful of earth and tamp the earth
down with the back of the spade.

In our years of observation of growers’ treatments and
in our own tests we have found that successful control of borers
with crystals is obtained with much less mounding than some
growers think necessary. On trees 10 years old, five or six
spadesful of earth are required to go around the base. Control
is not helped by adding more earth, nor should any appreciable
reduction be made in the amount used. See fig. 5.

Injury from PDB Crystals and Treatment of Young Trees

Much experimental work on peach borer control has been
done because of the fact that PDB may, under certain cir-
cumstances, injure peach trees. Typical injury is shown in
fig. 6. It may consist of only a slight flecking of the outer bark
layers, or of a coalescing of the flecks into dark spots. The spots
may be small, or they may be so large that they entirely girdle
the tree. They may affect only outer bark layers or they may
extend into the cambium.

The subject of injury to young peach trees by crystaline
PDB has been of little concern to Illinois growers. In 1920,
1921 and 1922, tests were conducted in a number of places in
southern Illinois on one-, two- and three-year old trees to study
this question, with the result that no injury was observed so
long as the crystals were not allowed to touch the bark. Asa

6 ILLINOIS NATURAL HisTORY SURVEY CIRCULAR 31 February

result of these’ tests we suggested in Circular 8* the use of
three-fourths ounce of the material on trees as young as two
years old and one-half ounce on younger trees, but we withheld

Fig. 6.—Injury from PDB (paradichlorobenzene) crystals, ranging from few flecks,
A, at the left side of the part of tree that has been cut, to blackened areas on the
right side, B.

unqualified recommendations until further experimental work
could be done. In Circular 267, published in 1935, we suggested
the use of one-half ounce on trees one full year old.

In the fall of 1937, tests conducted jointly by the Illinois
Natural History Survey and the United States Bureau of
Entomology and Plant Quarantine on trees of different ages
showed that the younger the trees the greater was the proba-
bility of injury. The 5- and 13-year old trees used in the test
were not injured. On the other hand, under circumstances of
rather high soil temperatures, 20 per cent of the two-year old
trees treated with one-fourth ounce PDB showed spots which,
though small, penetrated into and severely injured the cambium.

With nursery stock, 20 per cent of two-year rootstocks and
100 per cent of all June buds were severely injured by one-eighth
ounce PDB. From the tests made it appears unsafe to use
PDB crystals on nursery stock.

We are still of the opinion that orchard trees one full year
old or older can be treated with comparative safety. For 15
years, one- and two-year old trees in Illinois have been treated
with PDB crystals, and in the close contact which we have had
tore Sees See roe St Chanel: The Peach Borer and Methods of Control. Illinois Natural

+Chandler, S. C., and W. P. Flint. Insect Enemies of the Peach in Illinois. Illinois Natural
History Survey Circular 26. 1935.

1939 CHANDLER: PEACH TREE BORERS if

with the growers of the state we have never heard of or observed
any serious injury to or loss of trees from PDB correctly applied.
Undoubtedly, some injury takes place at times, but less than
might occur if the trees were left to the borers.

It is our suggestion that growers continue treating young
trees as in the past but that they consider first the need for
treatment. Many orchards are two or three years old before
showing any appreciable infestation, and growers should make
examinations to ascertain that treatment is needed before it is
apphed.

Removal of Mounds

A number of experiment stations advise the removal of
mounds from young trees in from three to six weeks after treat-
ment, because of the assumption that gas will become concen-

: e hig ¥:

Fig. 7.—Removing mounds. This operation should be completed by the first of July.

trated in the pores of the soil as increasing amounts of it are
evolved from the PDB crystals. We have felt that under IIli-
nois conditions sufficient gas will escape to prevent a damaging
concentration. Removal of mounds shortly after treatment is
almost never practiced in Illinois, and over a long period of
years we have detected no ill effects from leaving the mounds
until the following spring.

In the spring or early summer, however, mounds made the
previous year should be removed, fig. 7. A large proportion of
borer eggs are laid on the tree trunks at the ground line, and
many young borers enter the bark at the same place. To destroy

8 ILLINOIS NATURAL HiIsTORY SURVEY CIRCULAR 31 February

ae wes BS /-
Fig. 8.—Peach trees ranging in diameter from 12 inches to 17 inches are common in

old orchards in Illinois and require from 114 to 2 ounces of PDB crystals per tree for
peach borer control.

eggs and borers with the usual PDB mounding treatment,
successively higher mounds must be made each year, unless the
ground around the trees is leveled before the moths begin laying
eggs. Fig. 3 indicates that, in the peach growing region of
southern Illinois, moths begin emerging the last of June. There-
fore, growers have until the first of July to remove mounds made
the previous year. This gives them the opportunity to include
mound removal as a part of their spring disking and hoeing,
after first growth of grass and weeds has started.

Amounts of PDB Crystals for Trees of Different Ages

Fear of possible injury to trees has largely determined
amounts of PDB crystals recommended. In the first years of
our experimental work, we treated one-year old trees with as
much as three-fourths ounce PDB per tree on several occasions
without loss of a tree or even observable injury. Two tests with
114 ounces per tree on two-year old trees gave similar results.
Further tests, however, have shown that much smaller amounts
of PDB give borer control.

Basing our recommendations on data we have from Illinois
and other states, we suggest the use of one-fourth ounce PDB
crystals on trees one full year old, one-fourth to one-half ounce
on two-year old trees and three-fourths ounce on trees three to
five years old.

Amounts used on older trees should be proportional to the
circumference of the trunks. For most bearing trees, | ounce
per tree is sufficient, but in many orchards 1% ounces are
needed. We have in Illinois at the present time many peach
orchards 12 to 20 years old with trees having diameters of 12 to

1939 CHANDLER: PEACH TREE BORERS 9

17 inches, fig. 8. A test conducted on 13-year old trees revealed
that as much as 2 ounces of PDB may be necessary in some
cases. Results of the test are given in table 1.

Table 1.—Results of test in which various amounts of PDB were used on 13-year
old trees treated at Centralia, October 19, 1922, and examined November 10, 1922.

Amount PDB TREES BORERS BORERS TOTAL PER CENT OF
PER TREE TREATED ALIVE DEAD Borers Borers DEAD

1 ounce 10 4 23 27 85.2

116 ounces 10 5 47 52 90.4

2 ounces 10 1 59 60 98.3

Accuracy 1s important in the application of PDB crystals.
Such measures as spoonful or handful are inaccurate and may
result in damage to trees or ineffective treatment. Measuring
cups that hold an ounce of PDB crystals are supplied by in-
secticide dealers. These may be used when an ounce is the
specified dosage, or they may form the basis for the selection
of other measures holding the exact amount of crystals pre-
scribed.

Time of Application

Fall is the usual time of treating for the peach borer, but
we have many inquiries from growers who have discovered
after it is too late for fall treatment that they have a serious
infestation. They wish to know whether they should treat in

Fig. 9.—Method of obtaining results of peach borer tests; soil removed and worms
cut out with knife. This slow and laborious job was the only method of peach borer
control before the introduction of PDB.

10 ILLINOIS NATURAL HisTORY SURVEY CIRCULAR 31 February

the spring or wait until the following fall. Data pertinent to
these inquiries have been collected, fig. 9.

Comparison of Seasons.—Table 2 gives a summary of all
our fall and spring tests in which PDB crystals were applied in
the recommended amounts and at times and under conditions
of soil temperature which would be considered advisable for
orchard treatment. Data on those treatments applied under
unusual conditions have been omitted.

This table shows that spring treatments have given from
77.8 per cent to 95.2 per cent kill and have averaged 83.4 per
cent. The fall treatments have ranged from 85 per cent to 100
per cent kill and have averaged 94.2 per cent. The variation
over a period of 8 springs and 14 falls 1s shown in table 2.

Table 2.—Results of spring and fall treatments with PDB crystals for peach
borer in Illinois. This table includes data on all tests in which recommended
amounts of PDB were applied under normal orchard conditions.

SPRING APPLICATIONS FaLL APPLICATIONS

YEAR Trees Total Per Cent of Trees Total Per Cent of

Treated Borers Borers Dead ‘Treated Borers Borers Dead
1920 20 162 717.8 40 47 100.0
1921 90 93 81.7 130 127 98.4
1922 30 21 OS? 30 139 92.8
1923 20 36 83.3 60 120 85.0
1924 — — -—-— 39 78 94.9
1925 -— ae —— 30 66 87.9
1926 10 19 84.2 20 88 98.9
1929 -— = _— 20 23 95.7
1930 — —- —— 15 1 100.0
1932 --- = -— 20 49 98.0
1934 —- —- -_—- 20 S2 93.8
1935 10 41 92.7 20 56 98.2
1936 10 20 95.0 70 144 93.8
1937 25 55 te) 28 90 95.6
All years 215 447 83.4 542 1000 04.2

Best Dates for Spring Treatments.—Spring treatments
should be made as early as temperature conditions are favorable.
Temperature records kept in connection with tests indicate
that adequate control can be obtained when soil temperatures
in the mounds at the level of the material, fig. 10, are from 55 to
60 degrees for a few days. More rapid volatilization of PDB
crystals occurs when the temperature is somewhat higher. To
the grower, however, this information is not so important as an
answer to his question of when to treat. Date-of-treatment tests

1939 CHANDLER: PEACH TREE BORERS not

Fig. 10.—Soil thermograph and thermometer used in determining temperatures suit-
able for volatilization of PDB crystals.

were conducted in southern Illinois for a three-year period. A
summary of these tests is given in table 3.

Although not extensive, these tests indicate that treat-
ments with PDB crystals made in southern Illinois in April

Table 3.—Results of tests made to determine best spring dates for applying
PDB for peach borer control in southern Illinois. These results indicate that in the
latitude of Carbondale PDB crystals are consistently effective as early as the first
of May.

TREES BORERS BORERS ToTAL PER CENT OF
DATE OF TREATMENT TREATED ALIVE DEAD Borers’ BoreERS DEAD
March 31, 1920 10 42 12 54 DD) 2
April 15, 1920 10 30 15 45 3568
May 1, 1920 10 18 66 84 78.6
May 15, 1920 10 18 60 78 76.9
Check, no treatment 10 61 6 67 8.9
April 14, 1921 10 11 0) 11 0.0
May 2, 1921 5 0 5 5 100.0
May 17, 1921 15 1 15 16 93.7
April 15, 1922 10 0 3 3 100.0
May 1, 1922 10 0 8 8 100.0
May 15, 1922 10 1 9 10 90.0
Check, no treatment 10 14 1 15 6.7

12 ILLINOIS NATURAL HistoRY SURVEY CIRCULAR 31 February

give unsatisfactory results but that those made the first of May
and later are relatively effective. Spring treatments, however,
cannot be expected to give as good results as fall treatments.

Best Dates for Fall Treatments.—Two factors determine
optimum times for fall treatments: (1) date of latest entrance
by the borers and (2) soil temperatures. These are related to
two questions which growers ask: (1) How early should we
treat? (2) How late should we treat?

The moth emergence chart, fig. 3, shows that in southern
Illinois moths are still emerging in large numbers as late as
September 19, in moderate numbers as late as September 26
and in small numbers as late as October 3. Since all eggs are
not laid for some days after the moths emerge, it is evident that
borer attack in southern Illinois continues into October. The
presence of tiny borers always found late in October substanti-
ates this statement.

In an effort to learn whether borer attack in southern
Illinois orchards continues into October, trees of a Carbondale
orchard were treated at different dates in the late summer and
fall of 1923. Table 4 gives the results of these tests. It brings
out the fact that, even as late as September 15, the treatment
failed to kill 9.1 per cent of the borers which entered above the
mound, but that no live borers were found following the October
1 treatment.

Table 4.—Total number of borers found and live borers found above mounds
in treated orchard near Carbondale, 1923.

PER CENT OF

Date OF TREES NUMBER OF BORERS FOUND Bosna
TRE ATEN fikEanED Total Above Mound MounpD
August 18 10 7 4 Sel
September 1 10 iil 7 63.6
September 15 20 11 1 9.1
October 1 20 3S) 0 0.0
October 13 20 ia 0 0.0

We recommend that growers in southern Illinois do not
treat earlier than September 25 and that, preferably, they wait
until October 1.

The question of how late to treat probably could be
answered, as already indicated, by reference to soil tempera-
tures, 55 degrees F. being considered as about the minimum for
effective volatilization of the crystal PDB. There are at times

1939 CHANDLER: PEACH TREE BORERS 13

some difficulties in interpreting soil temperature records, and
they are not generally available. So the grower is desirous
of knowing what calendar dates he can depend upon for effec-
tive treatment.

Tests conducted near Carbondale over a period of eight
years show that treatment is consistently effective in southern
Illinois as late as October 15. A summary of the data on this
point, giving number of borers concerned and annual fluctuation
in control, is presented in table 5.

Table 5.—Results of tests made to determine best fall dates for applying PDB

for peach borer control in southern Illinois. These results indicate that in the
latitude of Carbondale PDB crystals are consistently effective as late as October 15.

TREES BORERS BORERS TOTAL PER CENT OF
DaTE OF TREATMENT TREATED ALIVE DEAD Borers Borers DEAD
October 14, 1920 10 0 15 lS) 100.0
October 17, 1921 10 0 5 5 100.0
October 12, 1922 10 0 5 5 100.0
October 19, 1922 20 1 59 60 98.3
October 13, 1923 20 14 63 77 81.8
November 1, 1924 10 D, 27 29 93.1
October 24, 1925 20 4 39 43 90.7
October 13, 1932 20 1 48 49 98.0
October 15, 1937 8 3 34 37 91.9
All treatments 128 25 295 320 92.2

Differences in weather between southern and central Ili-
nois indicate that the most favorable dates for treatments in
the latitude of Centralia are between September 20 and October
5. In peach districts north of Centrala, treatments should be
made between September 15 and October 1.

Every year we find numbers of growers desirous of treating
later than October 15. They inquire how much later they can
successfully treat. To answer this question, treatments have
been made over a period of years as late as the first week of
November. A summary of these data is given in table 6.

In the tests recorded in table 6, the 1920 treatments were
decidedly ineffective. In 1923 no treatments were made later
tian October 13, but as the results of the treatment made at
this date were only fair it 1s safe to assume that later treatments
would have given even lower rates of kill. The results in 1924
and 1937 were satisfactory, though not so good as would have
been obtained under higher soil temperatures.

From the data we have, we conclude that, in about three
out of five years, satisfactory control of peach borers can be

14 ILLiInois NATURAL HIsTORY SURVEY CIRCULAR 31 February

Table 6.—Results of tests with PDB crystals to determine effectiveness in
southern Illinois of treatments for peach borer control made as late as the first week
of November.

TREES BORERS BORERS TOTAL PER CENT OF
DATE OF TREATMENT TREATED ALIVE DEapD Borers’ Borers DEAD
November 1, 1920 10 16 10 26 38.5
November 3, 1921 10 0 6 6 100.0
October 13, 1923 20 14 63 Ha) 81.8
November 1, 1924 10 2 27 29 93.1
November 1, 1937 7 2) 22 24 91.7

obtained by PDB crystals as late as November 1 in the latitude
of Carbondale. We have made no similar tests farther north.

Frequency of Treatment

A very practical question asked by growers relates to
frequency of treatment. For two successive years, 30 orchards
were examined. These fell into three groups: One group was
treated one year before examination; one, two years before; and
one, three years before. In each orchard, 100 trees were ex-
amined. The test involved in all 6,000 trees located in 60
orchards. Table 7 gives the results of these surveys.

Table 7.—Borer-infested trees per 100 in orchards treated one, two and three
years before examination.

INFESTED TREES INFESTED TREES AVERAGE FOR
Trees Last TREATED PER 100 IN 1933 Per 100 In 1934 THE Two YEARS

One year before 6.2 14.3 10.3
Two years before 36.1 48.9 4225
Three years before 54.6 S6mo 55.6

This table indicates that on the average an orchard not
treated for two years will have four times as many borer-infested
trees as an orchard untreated for one year. The infestation does
not continue to increase at the same rate for the years following
the second, but trees untreated for three years have an accumu-
lation of unhealed injury not indicated in these data.

We conclude that if a. grower wishes to economize by de-
creasing the number of peach borer treatments, he could proba-
bly omit treatments for one year without much permanent
damage to his trees, since he would kill most of the borers the
following fall before they do considerable feeding. However,
we believe he would be very unwise to omit treatment for two
successive years.

1939 CHANDLER: PEACH TREE BORERS 15

A practice which has considerable merit and is economical
is known as ‘‘treat a year and patch a year.’ Growers who
follow it treat their trees thoroughly every other year. In alter-
nate years they patch; that is, they treat only those trees that
show, above the ground line, indications of borer infestation.

Removal of Grass and Weeds Before Treatment

Early directions for borer treatment included careful
cleaning of the ground around the base of the tree before apph-
cation of the crystals. As a result of these directions, many
growers have spent and some now spend altogether too much
time on this cleaning operation. Soon after the introduction of
PDB into Illinois for borer control, tests were begun to de-
termine the need for removal of grass and weeds or for prepar-
ation of the soil. They are summarized in table 8.

Table 8.—Results of tests to determine need for removal of grass and weeds
prior to treatment with PDB crystals.

Grass REMOVED Grass Not REMOVED

Number Total Per Cent Number Total Per Cent

TIME OF of Trees Number of Borers of Trees Number of Borers
TREATMENT Treated of Borers Dead Treated of Borers Dead
Fall, 1922 6 3 100.0 6 2, 100.0
Spring, 1923 10 15 80.0 10 21 5), d/
Fall, 1923 30 87 82.8 30 33 90.9
Fall, 1924 10 27 96.3 10 22 95.5
Fall, 1925 10 60 98.3 10 28 100.0
Fall, 1932 10 24 100.0 10 25 96.0
Fall, 1934 10 11 100.0 10 16 81.3
All treatments SO 227 Oil 2 SO 147 92.5

These tests, extended over seven seasons, show conclusively
that the removal of grass and weeds does not increase the control
of the borer. The only reason for the operation is to facilitate
the spreading of the crystals. The trees used in the plots in
which the grass was not removed had in most cases a consider-
ably thicker growth of grass around the base than is found in
the average orchard and were selected because of this fact.
Fig. 11 shows the extent of the growth in a typical orchard used
in the test.

Substitutes for PDB Crystals

Four characteristics are sought in any substitute for PDB
crystals: First, low cost; second, safety on young trees; third,

16 ILLINOIS NATURAL HisToRY SURVEY CIRCULAR 31 February

Fig. 11.—Typical tree with excess growth of grass and weeds around base as used in
grass removal tests.

efficiency; fourth, effectiveness at low temperatures. We con-
sider the first two characteristics the most important of the four.
Probably the hope of finding a safer substance has been the
greatest incentive in the search for a new material over the
country at large.

Although Illinois growers have little fear of serious injury
on young trees, there is real need for a safe material for use on
nursery stock. Certainly some injury from PDB crystals occurs
under certain circumstances to Illinois orchard trees. If a ma-
terial could be found combining all or even most of the desirable
characteristics suggested, a real contribution to peach borer
control would be made.

Solid Substitutes.—Four solid materials were tested during
the seasons of 1925 to 1930 inclusive, all of them proposed by
chemical or insecticide companies as possible inexpensive sub-
stitutes for PDB. None proved to be of value.

Liquid Substitutes.—Oliver I. Snapp of the United States
Bureau of Entomology and Plant Quarantine, in tests over a
period of years in Georgia, has shown that applications of cotton-
seed oil emulsion impregnated with PDB may be sprayed around

1939 CHANDLER: PEACH TREE BORERS 17

the base of peach trees with the probability of less injury from
it than from crystal PDB. His results show at least as good con-
trol with this combination as with the crystal PDB. From time
to time other liquids, not containing PDB, have been suggested
and tried.

In Illinois we have tested mineral oils as carriers of PDB
and have favored them because of their cheapness and avail-
ability. We have tested two materials not containing PDB,
dichloropentane and Scalecide, suggested by manufacturers of
insecticides. We have also tested soybean oil as a carrier of
PDB. In table 9 are summarized our tests with these materials
for the falls of 1934 and 1935 and the intervening spring.

Table 9.—Results of tests with liquids on peach trees 10 years old for control
of peach borer in southern Illinois, fall of 1934 and spring and fall of 1935.

NUMBER OF TREES TOTAL BorRERS PER CENT OF
TREATMENT SEASONS TREATED BORERS DeEap Borers DEAD

Liquids Containing PDB

PDB in Dendrol 3 30 83 80 96.4
PDB in Scalecide 2 20 Sil 49 96.1
PDB* in Scalecide 1 10 29 7 58.6
PDB in soybean oil 2 20 34 31 91.2

Liquids Without PDB
Dichloropentane,

1 ounce per tree Y 20 5S 37 69.8
Dichloropentane,

2 ounces per tree 3 30 87 83 95.
Scalecide, 1 in 8 2 20 45 10 DBP) 7s
Check, no treatment 3 35) 103 3 2.9
Crystal PDB, standard

(1 ounce per tree) 3 50 129 WAS 95.4

: *Bach tree received a dilution containing one-fifth ounce PDB as compared with 1 ounce in each
of the three other treatments containing PDB.

Our procedure when testing the PDB crystals in oils was
to dissolve 2 pounds of the crystals in 1 gallon of oil and dilute
with water to make 4 gallons. We then applied 1 pint of the
diluted mixture to a mature tree. This gave each tree 1 ounce of
PDB, the same dose it would receive in the crystal treatment.
Mounding was done as in the crystal method.

In the case of Scalecide without PDB, the directions of the
manufacturer were followed. The dirt was removed from the
base of the tree as for worming, gum rubbed off with a sack and
1 quart of a dilute mixture, 1 part of Scalecide to 8 parts water,

18 ILLINOIS NATURAL HIsTORY SURVEY CIRCULAR 31 February

sprayed at the,base of the tree. At the suggestion of the manu-
facturer, a similar dilution of Scalecide containing one-fifth
ounce PDB was tested in the same way.

Fig. 12.—Liquids for peach borer control may be poured around the tree, but this
method of application increases the problem of carrying liquid in the orchard.

Other liquids were either sprayed with a bucket sprayer or
poured, figs. 12, 13, 14. In the case of dichloropentane, 1 or 2
ounce dosages were applied per mature tree.

All of the tests recorded in table 9 were on trees 10 years of
age or older. No injury was observed following any of the treat-
ments, but Mr. Snapp, working with some of the materials in
Georgia at the same time on trees of various ages, reported very
severe injury with dichloropentane used at strengths which gave
good control.

The tests recorded in table 9 show that control as good as
that given by the standard PDB crystal treatment was ob-
tained by the application of. 1 pint Dendrol or Scalecide dilution
per tree when the dissolved PDB was used in amounts equal to
the standard. They show approximately the same control with
2 ounces of dichloropentane, and poor results with Scalecide
diluted 1 in 8.

In the late summer and early fall of 1937, the Illinois
Natural History Survey and the United States Bureau of En-

1939 CHANDLER: PEACH TREE BORERS 19

tomology and Plant Quarantine conducted cooperative experi-
ments in southern I]linois in which vegetable and mineral oils
were tested as carriers of PDB. Also tested were ethylene
dichloride and dichlorethyl ether, two liquids not containing
PDB. In table 10 are given results of these cooperative tests,
made under the direction of Mr. Snapp and the writer.

Tests recorded in table 10 show that control as good as
that with the standard PDB crystals was obtained with all ma-
terials tested except dichlorethyl ether, and that almost as good
control was obtained by a reduction of about 25 per cent in the
amount of PDB incorporated into the carriers. Cottonseed oil
gave a little better control than did the mineral oils when used
as a carrier of PDB. Injury by PDB was discussed on page 5.

Of the materials tested in this experiment, ethylene dichlo-
ride looks especially promising.

In tests conducted on nursery stock, so few borers were
found that control tests were not conclusive and they are not

Fig. 13.—Soil often needs some cup- Fig. 14.—A few shallow cuts may be
ping or working to prevent run-off of made with a spade in the soil around
liquid applied for peach borer control. peach tree to prevent run-off of liquid.

included in table 10. However, the finding of more borers in
the check plots than in the treated indicates that control was
obtained by the use of liquids containing very small quantities
of PDB. In one of the treated plots, each nursery tree received
a one-eighth ounce dosage of PDB in liquid; in the other plot,
each tree received one-sixteenth ounce.

Spraying and Pouring Liquids.—In the tests recorded in
table 10, most of the plots treated with liquids were divided into

20 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 31 February

Table 10.—Results of tests with liquids for control of peach borer, made in late
summer and early fall of 1937, the Illinois Natural History Survey and the United
States Bureau of Entomology and Plant Quarantine cooperating.

PER CENT
PLoT TREES TotTaL BorRERS OF BORERS
No. TREATMENT TREATED BoRERS DEAD DEAD
Materials Containing PDB
1 Crystal PDB, standard
13-year trees, 1 oz. per tree 10 32 32 100.0
5-year trees, 34 oz. per tree 10 21 20 95.2
2-year trees, 14 oz. per tree 10 0 0 —S
2 PDB in cottonseed oil emulsion*
13-year trees, 1 oz. in 14'pt. per tree 10 33 33 100.0
13-year trees, 34 oz. in 14 pt. per tree 10 26 24 92.3
5-year trees, 34 oz. in 14 pt. per tree 10 15 15 100.0
5-year trees, 14 oz. in 14 pt. per tree 10 4 4 100.0
2-year trees, 14 oz. in 4 pt. per tree 10 0 0 ——-
2-year trees, 14 oz. in \% pt. per tree 10 0 0 -_—
3. PDB in mineral oil emulsion?
13-year trees, 1 oz. in !4 pt. per tree 10 32 29 90.6
13-year trees, 34 oz. in 14 pt. per tree 10 41 39 95.1
5-year trees, 34 oz. in 14 pt. per tree 10 8 8 100.0
5-year trees, 4 oz. in 14 pt. per tree 10 39 38 97.4
2-year trees, 14 oz. in \ pt. per tree 10 2 2 100.0
2-year trees, 1g oz. in 4 pt. per tree 10 2. 1 50.0
4 PDB in equal parts cottonseed
and mineral oilf emulsions
13-year trees, 1 oz. in 44 pt. per tree 10 56 52 92.9
13-year trees, 34 oz. in 14 pt. per tree 10 61 60 98.4
5-year trees, 34 oz. in 14 pt. per tree 10 17 17 100.0
5-year trees, 14 oz. in 1% pt. per tree 10 6 6 100.0
2-year trees, 4 oz. in 14 pt. per tree 10 4 4 100.0
2-year trees, 14 oz. in 4 pt. per tree 10 5 5 100.0
7 PDB in Dendrol
13-year trees, 1 oz. in 44 pt. per tree 10 37 36 97.3
5-year trees, 34 oz. in 14 pt. per tree 10 6 100.0
2-year trees, 14 oz. in 4 pt. per tree 10 3 3 100.0
Materials Not Containing PDB
5 Ethylene dichloride emulsion
13-year trees, 14 pt. 25% emulsion
per tree 10 76 76 100.0
13-year trees, }5 pt. 20% emulsion
per tree 10 30 29 96.7
5-year trees, 15 pt. 20% emulsion
per tree 10 13 13 100.0

5-year trees, 15 pt. 15° emulsion
per tree 10 0 0 ==

1939 CHANDLER: PEACH TREE BoRERS 21

Table 10—Concluded.

PER CENT
ROR TREES ToTaAL BoreERS OF BOoRERS
No. TREATMENT TREATED BorERS DEAD DEAD
2-year trees, 14 pt. 20% emulsion
per tree 10 5 5 100.0
2-year trees, 14 pt. 159% emulsion
per tree 10 3 3 100.0
12 Dichlorethyl ether dissolved in water at
rate of 30 cc. in 1 gal.
13-year trees, 1 pt. per tree 5 16 3 18.8
13-year trees, 34 pt. per tree 5 15 9 60.0
5-year trees, 14 pt. per tree 5 0 0
6 Check, no treatment
13-year trees 5 43 2 4.7
5-year trees 5 35 3 8.6
2-year trees 10 5 0 0.0
*All emulsions, 50 per cent stock. Viscosity, 491.4.

two parts; in one part the liquids were sprayed at the base of
the tree with a bucket sprayer and in the other the liquids were
poured, fig. 12. A summary of all the results gives the following
percentages of dead borers: 96.1 per cent in plots in which the
liquid was sprayed; 97.7 per cent in plots in which the liquid
was poured. Under certain circumstances it might be of im-
portance to know that liquids give as good results when poured
as when sprayed.

Comparison of Solids and Liquids

The use of PDB crystals for peach borer control, now a
long established practice, is relatively cheap, requires very
little skill or equipment and is effective. Although under
certain conditions some injury occurs, growers are not likely to
make a change unless they can see sufficient advantages. For
this reason we have tried to explore all the possible advantages of
the liquid method and to compare them with those of the crystal
method.

Injury.—Injury by PDB has already been discussed on
page 5. No material has yet been found that we are certain will
give no injury under any circumstances, but some effective
liquids, such as ethylene dichloride and PDB in cottonseed oil
emulsion, are apparently a little safer than PDB crystals.

Effectiveness at Low Temperatures.—Because of their

Dy ILLINOIS NATURAL HisToRY SURVEY CIRCULAR 31 February

physical characteristics, liquids are likely to become effective
more quickly than solids. For this reason they might be effective
at lower temperatures or might utilize to better advantage very
short periods of high temperature. Tests with ethylene dichlo-
ride made in New York state by Mr. Snapp gave good results at
low temperatures.

A test of ethylene dichloride emulsion was begun Novem-
ber 18, 1937, in southern Illinois at soil temperatures which
remained almost stationary at 35 degrees F. during the first
four days, varied from 30 to 40 degrees during the next four
days and attained a maximum of 52 degrees on the two days
before the examination, 11 days after treatment. On December
3, a treatment was made with this material and with crystal
PDB for comparison. Temperatures following this treatment
ranged only from 35 to 40 degrees. Examinations were made on
December 16. Table 11 gives the results of these tests.

Table 11.—Results of tests for effectiveness of ethylene dichloride used against

peach borers in southern Illinois at low temepratures ranging from 30 to 52 degrees
F., autumn, 1937.

MATERIAL, DATE OF TREATMENT TREES TOTAL Borers PER CENT OF
AND TEMPERATURE RANGE TREATED BORERS DeEap Borers DEAD

Ethylene dichloride,
November 18, 30-52 degrees 10 41 34 82.9

Ethylene dichloride,

December 3, 35-40 degrees 5 20 18 90.0
PDB crystals,
December 3, 35-40 degrees 5 10 1 10.0

Apparently ethylene dichloride has the advantage of being
effective at lower temperatures than is crystal PDB. .

Further tests under conditions of cold soil were conducted
in March, 1938, in Jackson and Johnson counties by the Illinois
Natural History Survey, represented by the author, and the
United States Bureau of Entomology and Plant Quarantine,
represented by Mr. Snapp. Three weeks intervened between
treatment and worming. In this time, soil temperatures
averaged each week from 50.2 to 55.3 degrees with minimums of
43 and a maximum one day only of 64. Ethylene dichloride
emulsion and dichlorethyl ether, each at different strengths,
were compared with crystaline PDB on trees of three different
ages. Table 12 summarizes the results.

1939 CHANDLER: PEACH TREE BORERS 23

Table 12.—Results of tests for control of peach borer by ethylene dichloride
emulsion and dichlorethyl ether under conditions of low soil temperature at Car-
bondale, March, 1938.

AGE OF AMOUNT TREES ToTaAL PER CENT OF
TREES MATERIAL USED PER TREE TREATED BorERS BoreERS DEAD
10 years Ethylene dichloride VY pt. of 25% 20 134 97.0

10 years Ethylene dichloride V6 pt. of 20% 20 186 9275

10 years Dichlorethyl ether i joWrS* 10 60 96.7

10 years Dichlorethyl ether 34 pt.* 10 46 OS

10 years PDB crystals il Le 10 35 34.3

10 years Check, no treatment == 5 28 0.0

4 years Ethylene dichloride V4 pt. of 20% 10 85 97.6

4 years Ethylene dichloride 14 pt. of 15% 10 53 96.2

4 years Dichlorethyl ether ¥%, pt.* 10 96 92.7

4 years Dichlorethyl ether Vy pt.* 10 112 a

4 years PDB crystals 34 OZ. 10 116 87.1

4 years Check, no treatment 5 80 0.0

2 years Ethylene dichloride \y pt. of 15% 20 52 92.3

2 years Ethylene dichloride 4 pt. of 124% 20 51 94.1

2 years Dichlorethyl ether Vou per 10 35 82.9

2 years Dichlorethyl ether Yn Dio 10 WD, 81.8

2 years PDB crystals VY oz. 10 54 16.7

2 years Check, no treatment 5 14 0.0

*Diluted, 30 cc. dichlorethyl ether to 1 gallon water.

This experiment indicates that ethylene dichloride emul-
sion applied at strengths shown in table 12 will give very
effective control of the peach borer at temperatures which are
not high enough for good control by PDB crystals. It also
indicates that dichlorethyl ether may give fairly good control
under these conditions. The experiments made in the late
summer and early fall, when soil temperatures were higher,
were not very favorable to dichlorethyl ether, table 10.

Necessity for Mounding.—Because of their physical state,
it is conceivable that liquids applied for peach borer control
might not need mounding. This conception was tested during
the spring and fall of 1936. PDB was dissolved in Dendrol at
the usual rate of 2 pounds of crystals to 1 gallon of the emulsion
and diluted with water so that when each tree was treated with
1 pint of material it received 1 ounce of PDB. Four tests were
conducted in two orchards over two seasons. Trees were 10 and
11 years old. Table 13 gives the results.

Table 13 shows only one test in four in which control in
unmounded trees equaled or bettered that in the mounded,
and the averages for the 210 trees treated and nearly 500 borers

24 ItLinors NATURAL HIstoRY SURVEY CIRCULAR 31 February

concerned showed a kill that was 21.6 per cent less in the un-
mounded than in the mounded trees. Obviously, liquid treat-
ment does not lessen the necessity for mounding.

Table 13.—Results of tests to determine necessity of mounding after liquid
treatments.

TREES MOUNDED TREES Not MoOuNDED
TEST Trees Total Per Cent of Trees Total Per Cent of
NuMBER Treated Borers Borers Dead Treated Borers Borers Dead
1 0 22 100.0 10 22 86.4
2 25 Sy 90.4 25 130 68.5
3 50 107 oy a) 50 96 70.8
4 20 40 Aes) 20 25 88.0
All tests 105 291 04 1 105 273 (Zee

It has been stated that mounds for trees given the liquid
treatment need not be made so large as those for trees given the
crystal treatment, fig. 5, and need not be tamped down. We
have made no tests to determine the validity of this statement,
but in view of the above experiment it seems rather doubtful.
In the 1937 cooperative experiment, results of which are shown
in table 10, liquid-treated trees were given a minimum amount
of mounding and no tamping, but no comparison was made
with crystal-treated trees with respect to size of mounds.

Equipment Required.—The liquid treatment requires the
handling of 8 to 16 times as much weight as does the crystal
treatment.

The most economical method of applying the liquid is
usually with the power sprayer, which the orchardist already
possesses. The life of a spray machine and the cost of mainte-
nance is, in general, inversely proportional to the amount of use
given it. Estimates from growers of large acreages in Illinois
indicate that the cost is approximately $2 in depreciation, re-
pairs and upkeep, not including gasoline and oil, to operate a
sprayer for one day. In an actual test, described below, one-
half gallon of gasoline at 18 cents per gallon was required to
operate a sprayer one hour. To the cost of the sprayer must be
added the expense involved in having it pulled by a team or
tractor.

A regulator has been devised, fig. 15, which may be at-
tached at the end of the spray hose for liquid treatments. This
is necessary so that the right amount of liquid, no more and

bho
on

1939 CHANDLER: PEACH TREE BORERS

no less, may be applied to each tree. Selling at the present time
for $20, this piece of equipment could be made by a mechanically
trained grower for less if his time were not considered, and

Fig. 15.—Regulating device in operation. With this device a measured half pint or
pint of liquid can be sprayed around the base of trees for peach borer control.

probably if any great demand should develop it could be pro-
duced commercially more cheaply than at present. Every man
applying the liquid must be equipped with the device, and the
number of men working at this operation is limited by the
supply of regulators.

The fact has been brought out on page 21 that, in the
application of the liquid, pouring is as effective as spraying.
If liquid were poured around each tree, the use of the sprayer
and regulating device would, of course, be eliminated. How-
ever, the problem of carrying the necessary large amount of
liquid from tree to tree remains. The amount of time required
by this method and present labor prices must be considered in
figuring its cost.

Time Required.—In the spring and fall of 1937, two tests

26 ILLINOIS NATURAL History SURVEY CIRCULAR 31 February

were run under orchard conditions to determine the actual time
required to treat by the liquid and the crystal methods. In the
Hartline Orchards, Union County, the tests covered an area of
714% acres. In the Heaton Orchards, Johnson County, they
covered about 18 acres.

In all orchards, the liquid treatment was given by one
man with a power sprayer and a regulating device; the pressure
in the sprayer was reduced to 100 pounds. No driver except the
operator was used, a saving that is possible only with steady,
dependable teams. Two men followed the sprayer, mounding.
Time-out was taken for every interruption, so that the records
include only the actual time of work. In the crystal-treated
blocks of the Heaton Orchards, records were kept of a crew of
nine men, three to apply the crystals and six to mound.

The average time required to treat and mound a tree was
1.4 minutes by the liquid method and 2.0 minutes by the crystal
method, or a saving of 30 per cent in time by the liquid method.

On the basis of a common wage in Illinois orchards, 15
cents per hour or one-fourth cent per minute, the following cal-
culations were made:

Liquid treatment, 1 tree (1.4 man-minutes) cost
$0.0035 (about one-third cent).

Crystal treatment, 1 tree (2.0 man-minutes) cost
$0.0050 (one-half cent).

It therefore cost $0.0015, approximately one-seventh cent,
more per tree for labor to treat by the crystal than by the liquid
method.

In these tests, 3 gallons of gasoline were required to keep
the engine running for 6 hours. This was equivalent to 5
gallons for a 10-hour day. Oil and gas together for a day cost
at least $1. The average number of trees treated by a sprayer in
one day was 427. The cost of the gas and oil, therefore, amounted
to $0.0023 (about one-fourth cent) per tree, approximately 50
per cent more than the amount saved by the greater speed of
the liquid method. The item of $2 per 10-hour day for deprecia-
tion and repair of spray rig added another $0.0047 (about one-
half cent) per tree to the cost of the liquid treatment.

The cost of such items as filling the spray rig, heating and
preparing the material, hitching and unhitching the team, and
repairing possible spray-rig breakage was not considered in
the calculations.

Cost of Materials.—Price of the material is another im-

1939 CHANDLER: PEACH TREE BORERS 27

portant item in a comparison of liquid and crystal treatments.
At a retail price of 18 cents per pound in 100-pound lots, the
price which now prevails, and at the amount of 1 ounce PDB
per tree, the cost of the material for the crystal treatment is
slightly more than 1 cent per tree, or about twice the cost of
the labor required to apply it. Obviously, the cost of oils used
as carriers must be considered. Prices of these materials vary
from year to year, but, if used at the dilutions indicated, even
the cheapest of the carriers will add from three-fourths to 1
cent per tree, which almost doubles the cost of materials.

The greatest hope for economy is from the materials which
do not contain PDB. Ethylene dichloride at the present price
of 614 cents per pound in 50-gallon drums costs approximately
1 cent per tree. Dichloropentane can now be obtained for 5 cents
per pound in single barrel lots. If this is applied at the rate of
2 ounces per tree, the cost is about $0.007 (slightly less than
three-fourths cent) per tree. However, insufficient work has
been done with this material, and because of severe injury in
Georgia we do not at the present time recommend it.

Summary of the Solid and Liquid Methods.—-Following is a
summary of the facts that have become apparent through com-
parison of the solid and liquid methods of treating for peach
borer control:

1.—To date only one solid, crystal PDB, is known to be
both safe enough and cheap enough to use.

2.—Four liquid substitutes tested, cottonseed oil emulsion,
mineral oil emulsion and miscible oils, all impregnated with
PDB, and ethylene dichloride emulsion (without PDB) are as
effective under normal treating temperatures as PDB crystals.
These substitutes appear to be a little less likely to injure the
tree than are the crystals.

3.—When the soil is cold, ethylene dichloride emulsion is
more effective than PDB crystals.

4.—Mounding is necessary after liquid treatments, though
possibly the mounds need not be so large as when crystals are
applied.

5.—Cupping may be necessary under certain soil condi-
tions to prevent run-off when liquids are used.

6.—Liquid substitutes found safe and efficient are all more
expensive than PDB crystals with the exception of ethylene
dichloride emulsion, which costs about the same.

7.—The liquid method of treating trees is 30 per cent

28 ILLINOIS NATURAL History SURVEY CIRCULAR 31 February

faster than the crystal method if the liquid is sprayed on the
trees with a gasoline driven machine.

8.—The use of a spray machine for applying the liquid
entails the purchase of a special regulating device which limits
the number of operators.

9.—Under Illinois conditions the financial gain from the 30
per cent saving in time, possible with the liquid treatment, is
offset by any one of several items of expense connected with the
use of a sprayer and team.

10.—If the liquid material is poured around the trees, no
time is saved, and the carrying into the orchard of weight eight
times that of crystal PDB necessitates the use of a team and
probably is more expensive and less simple an operation than
the crystal treatment.

THE LESSER PEACH BORER

As the lesser peach borer, Synanthedon pictipes (G. & R.),
works in crotches and wounds of peach trees, fig. 16, rather than
at the base, it does not girdle the trees. It is termed “‘lesser”’

{

Fig. 16.—Injury caused by lesser peach borer, Synanthedon pictipes (G. & R.).

1939 CHANDLER: PEACH TREE BORERS 29

Fig. 17.—Wounded areas and weakened crotches on peach trees are especially sub-
ject to attack of lesser peach borer.

because the damage it does is not so great as that done by the
peach borer, Conopia exitiosa (Say).

Extent of Injury

In our observations we have found the lesser peach borer
working usually in places on the tree previously weakened or
injured. Weakened crotches, areas on the trunk skinned by a
tractor, sun-scalded and winter-injured branches, and branches
broken by heavy crops are favored places of attack, fig. 17.
There is evidence to show that some of the splitting of crotches
which occurs would be avoided if it were not for the additional
weakening caused by the borers working at a critical point.
Needless to say, any horticultural practice that will avoid
injuries to the trees will help to control this insect.

In order to learn something of the prevalence of the lesser
peach borer in actual percentages, examinations were made in
10 representative commercial orchards of bearing age in south-
ern Illinois. Fifty trees, scattered over each orchard, were ex-
amined and a record made of the infestation. A tree with one
or more injured areas was classed as infested.

Degree of infestation among the orchards ranged from 10

30 ILLINoIs NATURAL History SURVEY CIRCULAR 31 February

to 32 per cent. Of all trees examined in the 10 orchards, 22.6
per cent were infested with the lesser peach borer.

Control Measures

Since the lesser peach borer usually works too high on the
tree to be covered with a mound, most growers have relied on
the old jack-knife and wire method formerly used on the peach
borer, fig. 9. With the introduction of the liquid method of
peach borer control, it was suggested by Mr. Snapp that some
of the materials used would control the lesser peach borer.
In our control experiments for this latter insect, we used ma-
terials at strengths sufficient for peach borer control and also
at even greater strengths.

Experimental Work

In our observations of liquid applications for the peach
borer in actual orchard practice, it was evident that the operator
has neither liquid enough in the half pint or pint applied per
mature tree, or time enough before his automatic cut-off stops
him, to treat anything but the base of the tree, and he is not
likely in this one operation to do any treating for the lesser
peach borer.

For this reason we confined our tests to painting the affected
areas, fig. 18. When the gum could easily be removed, this
was done before the material was applied, but when, as often

Table 14.—Results of experiments for control of lesser peach borer by insecti-
cides painted on affected areas. The experiments cover spraying seasons in the
years 1934-37.

STOCK, DILUTION, PER CENT
POUNDS OUNCES OF
MATERIALS PDB PER PDB PER SEASONS TREES TOTAL BORERS
UsED GALLON PINT TESTED TREATED BORERS DEAD
PDB in Dendrol 2 1 3 38 47 Sie
PDB in Dendrol 2 » 5 70 83 86.7
PDB in Dendrol 4 4 D 35 27 100.0
PDB in soybean
oil 2 mal 1 10 23 8.7
PDB in Niagara
Tar Oil 2 2 1 10 16 93.8
PDB in Niagara
Tar Oil 2 4 (Un- 1 10 10 100.0
diluted)
Dichloropentane — Undiluted 1 10 24 70.8
5 45 47 .0

Checks — —

1939 CHANDLER: PEACH TREE BORERS 31

was the case, the gum had hardened it was left undisturbed.
Good penetration of the gas, however, resulted even in the
latter situation, and excellent control was obtained. The ma-
terials tested were those used for peach borer control with the
addition of one other. They are indicated in table 14, which
gives the results of the experiments.

No injury could be observed in the areas receiving any of
the materials. The infested areas are usually somewhat corky
and protected by outer bark and by several layers of inner bark.
If the paint is applied chiefly to the place showing infestation,
there seems to be little danger of injury, even at the strengths
used. In one of the tests, the lower half of tender shoots of the
current season, growing up in the center of the tree, were
painted; the upper parts were left for checks. With the dichloro-

“7? : ee t
29r-eoe

»< *.%
af, +

Fig. 18.—Control of lesser peach borer by painting affected areas of the tree with
PDB-oil solution. Even a boy with a bucket of material can treat a large number of
trees in a few hours.

32 ILLINOIS NATURAL HisTORY SURVEY CIRCULAR 31 February

pentane and the PDB in Dendrol diluted 2 ounces to 1 pint,
injury occurred on from 10 to 25 per cent of the shoots, al-
though no injury whatever could be found on the affected
areas of the older wood.

Examination of table 14 shows that rather disappointing
results were obtained with the strength of PDB in Dendrol
which gave very satisfactory control for the peach borer when
mounding was done. This strength was 2 pounds PDB to 1
gallon Dendrol, diluted with water so that each pint of the mix-
ture contained 1 ounce of PDB. However, when that strength
was doubled to 2 ounces PDB per pint of mixture, 86.7 per cent
kall was obtained as a five-year average.

An attempt was made to increase this strength by dis-
solving 4 pounds PDB in Dendrol and diluting so that each
pint of mixture contained 4 ounces PDB. Although this mix-
ture gave better control than the one containing 2 ounces PDB
to the pint, it was not satisfactory because of the trouble in-
volved in incorporating such a large amount of the crystal into
the oil, the difficulty of keeping it from crystalizing out on
cooling and the danger of injury. The same strength could have
been obtained by using 2 pounds of PDB to 1 gallon of Dendrol
and applying without dilution, but it was found that spreading
qualities of the paint are much improved when it 1s diluted with
water.

It is probably best in using Dendrol to keep close to the
proportion of 2 pounds PDB to 1 gallon of the oil and to the
dilution of 2 ounces PDB to 1 pint of mixture.

It may be-seen in table 14 that the tar oil used gave in
the two tests somewhat better control than the miscible oil.
Although no injury occurred in our tests, it should be borne in
mind that there is a greater probability of injury from a tar
oil than from a miscible oil. After five seasons of tests, we do
not hesitate to suggest the use of PDB in a miscible oil at the
rate of 2 pounds PDB to 1 gallon of oil diluted with water so
that there are 2 ounces PDB to 1 pint of mixture.

In making up this material for use in the orchard, if all the
stock is to be diluted, 2 pounds of the crystal dissolved in 1
gallon of the miscible oil should be diluted with water to make 2
gallons of mixture. If only a portion of the stock is used, it
should be diluted at the rate of 6 parts by volume of the oil-
PDB mixture to 4 parts of water. This will give slightly more
than 2 ounces PDB to 1 pint of the diluted mixture.

1939 CHANDLER: PEACH TREE BORERS 33

This method of treating lesser peach borers is relatively
cheap. A man or even a boy with a bucket of material can
cover a large area in a day, examining trees and painting only
the spots showing injury. In a trial test over a limited area, 1
pint treated all the infested areas on eight trees. With the
material used, PDB in Dendrol, the cost amounted to one-half
Genii per tree:

Time of Treatment

Lack of information on the life history of the lesser peach
borer in Illinois makes it impossible to state definitely the best
times to treat for it. Our observations indicate that emergence
starts earlier in the season than is the case with the peach borer,
and it seems probable that treatments should be made in the
fall rather than in the spring. The occurrence of a second brood
in Illinois is indicated by studies already made in Ohio and
West Virginia. With our present knowledge of the insect, we
suggest treatment about the same time in the fall as for the
peach borer.

THE PEACH BARK BEETLE AND THE SHOT-HOLE
BORER

The peach bark beetle, Phthorophloeus limnaris (Harr.),
and the shot-hole borer, Scolytus rugulosus Ratz., attack the
trunk and branches of peach trees in Illinois, working especially
on weakened trees and branches, figs. 19, 20, 21, 22. The best
method of control is to correct whatever has caused the weak-
ness, such as lack of nitrogen, poor drainage, attacks of scale
or peach borers, lack of care and cultivation, or winter injury.
This is not always possible, however, and at times these insects
attack apparently healthy trees. There is need for direct con-
trol by insecticides.

Our control experiments with these insects began in 1931
with a test of PDB in cottonseed oil sent by Mr. Snapp from
the federal laboratory at Fort Valley, Ga. A kill of 96.5 per
cent resulted from the first test.

The following year the same material, possibly deteriorated
by this time, was used in another test, and, though as good
control was secured, very severe injury and killing of branches
resulted, which discouraged us from further trials until the fall
of 1935 when tests were started with PDB and miscible oil
mixtures.

34 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 31 February

Fig. 19.—Weakened peach branch showing injury by bark beetles, Scolytus rugulosus
Ratz. Note tiny holes made by beetles, some of holes filled with exuding gum.

Fig. 20.—Branch of peach infested with bark beetles. The bark has been pulled off
to show the white grubs in position.

1939 CHANDLER: PEACH TREE BORERS 35

In tests made in 1935, 1936 and 1938 for control of the
shot-hole borer, PDB was dissolved in Dendrol at the rate of 2
pounds of PDB to 1 gallon of Dendrol. This solution was diluted

Fig. 21.—An infested peach branch that Fig. 22.—Results of bird attack on peach
shows burrows of the bark beetle. branch infested with bark beetle.

with water. Part was diluted so that each pint of mixture con-
tained 1 ounce of PDB and part so that each pint contained 2
ounces of PDB. Table 15 shows the results obtained.

These tests indicate that with the PDB-Dendrol mixture
it is possible to attain good control of the beetles but not of the
grubs of the shot-hole borer. The reason for this apparently lies
in the fact that the beetles stay close to the holes they have made
in the bark, whereas, the grubs, after hatching, tunnel too far

Table 15.—Results of 1935, 1936 and 1938 tests for control of shot-hole borer*

by PDB in Dendrol, a miscible oil. Both beetles and grubs of the shot-hole borer
were present in the 1936 and 1938 tests.

DILUTION,
OUNCES

YEAR PDB PER TOTAL PER CENT OF TOTAL PER CENT OF
TESTED PINT BEETLES BEETLES DEAD GRUBS GruBs DEAD
1935 1 ounce 9 DD. —- —

2 ounces 8 1S -

Check 18 0.0 —
1936 2 ounces 26 100.0 10 0

Check 15 6.7 20 0
1938 2 ounces 89 98.9 362 if faa

Check 66 0.0 337 0.0

*Determined by Dr. H. H. Ross as Scolytus rugulosus Ratz.

36 ILLinois NATURAL History SURVEY CIRCULAR 31

from the openings for the gas to penetrate. It appears necessary
to treat when the beetles have first attacked the trees and before
they have laid eggs.

_ RECENT PUBLICATIONS

of the Illinois State Natural History Survey

A.—ILLINOIS NATURAL HISTORY SURVEY BULLETIN.

Volume 21, Article 1.—The Effect of Petroleum-oil Sprays on Insects and Plants. By
M. D. Farrar. November 1936. 32 pp., frontis. + 21 figs., bibliog. Contents: Fore-
word; Properties of oil emulsions; Effect of petroleum oils on plants; Insecticide
tests with the emulsions; Oils with fungicides.

Volume 21, Article 2.—Responses of the Large-mouth Black Bass to Colors. By Frank
A. Brown, Jr. May 1937. 23 pp., frontis. + 10 figs., bibliog. Contents: Problem
of color vision in fishes; Materials for the experiments; Training and responses of
large-mouth black bass; Interpretation of the responses; Summary. 50 cents.

Volume 21, Article 3.—Studies of Nearctic Aquatic Insects. By H. H. Ross and T. H.
Frison. September 1937. 52 pp., frontis. + 86 figs., bibliog. Contents: I. Nearetie
alder flies of the genus Sialis (Megaloptera, Sialidae) by H. H. Ross; and IL.
Descriptions of Plecoptera, with special reference to the Illinois species, by T. H.
Frison. 50 cents.

Volume 21, Article 4.—Descriptions of Nearctic Caddis Flies (Trichoptera) with
special reference to the Illinois species. By Herbert H. Ross. March 1938. 83 pp.,
frontis. + 123 figs., foreword, index. $1.00.

B.—ILLINOIS NATURAL HISTORY SURVEY CIRCULAR.

28.—Rout the Weeds! By L. R. Tehon. August 1937. 34 pp., color frontis. + 8 figs.
Contents: The importance of weeds; Weeds as economic factors; Weeds as harbor-
ers of plant diseases; Relation of weeds to public health; Control methods; Eight
pernicious weeds of Illinois—common ragweed, giant ragweed, poison ivy, poison
sumac, wild parsnip, white snakeroot, pokeweed, common burdock.

29.— Windbreaks for Illinois Farmsteads. By J. E. Davis. April 1938. 18 pp., frontis. +
12 figs. Contents: Planning the windbreak; Planting the windbreak; Care of the
windbreak; What the windbreak trees are like.

30.—Outwitting Termites in [linois. By W. E. McCauley and W. P. Flint. June 1938.
20 pp., frontis. + 19 figs. Contents: Termites and their habits; Structural control
of termites; Chemical control of termites; Unified action against termites.

C.—ILLINOIS NATURAL HISTORY SURVEY MANUAL.

1.—Fieldbook of Illinois Wild Flowers. By the staff. March 1936. 406 pp., color
frontis. -+ 349 figs., index. Contents: Introduction; Key to families; Description
of species (650). $1.50.

Address orders and correspondence to the Chief
ILLINOIS STATE NATURAL HISTORY SURVEY
Natural History Bldg., Urbana, IIl.

Payment must accompany requests for publications, in the form

of U.S. Post Office money order made out to State

Treasurer of Illinois, Springfield, Illinois.

lil ug

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