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7ebriary 1944 1-61
UNITED STATES DBPAMTMJNT 07 AGRICULTURE
Agricultural Research Administration
SBureau of Intomology and Plant QCuars-ntine
MXTETL BFDMIDZ FUMIGATION 07 JURSIET STOCI
FOR THE ORIBMTAL FRUIT MOTE
By Bandall Latta and A. C. Johnson,
Division of Control Investigations
Prior to 1938 several western States imposed quarant'"nes against
nursery-etook hosts of the oriental fruit moth (Grapholitha molest.
(Busck)), Including almond, apple, apricot, cherry, chokecherry,
hawthorn, nectarine, peach, pear, plum, quince, and ornamental forms
of the same, which prohibited the entry of nursery trees If they origi.-
nated in areas known to be infested with that insect. In i937 studies vee
begun to determine whether methyl bromide fumigation would effectively
destroy overwintering larvae of this insect so that nursery hosts
might be shipped without risk of disseminating it.
The problem was divided into three phases, (1) the development
of lethal fumigation schedules for the insect, (2) a study of the ef-
fect of fumigation upon dormant nursery trees, and (3) the development
of equipment and methods of procedure for commercial application by
The data concerning the firs,phaee have been pubiishe4 by
Johnson et al.!/ and by Hawkines. -
Following the publication by Hawkins, quarantines of western
States were amended in the fall of 1938 to accept nursery trees
f=am gaad with a prescribed dosage schedule of 3.5 lbs/e hr.. at
70O 7,21 On the basis of further experimental studies, they were
amended again in 1939 to change the prescribed schedule to 3 lbs/4 hrs.
at 600, or 2 lbe/4 hrs. at TO7'* F.
l/ Johnson, A. C., 1. M. Livingstone, and J. VW. orer, 12.
Methyl bromide fumigation to control oriental fruit moth on dormant
nursery stock. Jour. Icon. Int. 35 (5): 6 -6T7.
j/ Hawkins, Lon A. 19385. Fumigation of dormant deciduous nursery
stook for the oriental fruit moth with methyl bromide. U. S. Dept. Agr.,
Bur. Bnt. and Plant Quar. "L458 processedd).
3/ For the sake of conciseness all dosage schedule@ are abbreviate&
in symbol form as follows 3.5 lbe/4 hrs. at 70 7. w 3.5 pounds of
methyl bromide for 4 hours at a temperature of 70' 1. All dosages are
in pounds per 1,000 cubic feet of vault space.
The results of studies on the effect of fumigation on dormant
nursery trees and. of the development of equipment and methods of
procedure for commercial use are presented herein.
Ixperimental Studies on the Effect of Fumigation on Dormant Nursery Trees
Concurrently with the studies on larval mortality resulting from
fumigation, extensive experiments were conducted to test the reaction
of dormant nursery trees to effective fumigation schedules. A majority
of these tooests were made in Missouri in cooperation with the State
Department of Agriculture V and. interested nursery companies. Other
tests were in cooperation with a nursery company in Maryland, and still
others were done at the Beltsville Research Center, Beltsville, Md.
These tests were made from 1937 to 1942.
Tolerance of Nursery Trees Except Apple
Two varieties of peach trees were fumnigated in Noew Jersey on
February 24, 1937, with a dosage of 3.5 lbs/3 hro. at 70T 7. without
Six varieties of peach, two of cherry, one of pear, six of plum,
two of apricot, and one of quince were fumigated in Pike County, Mo.,
in January 1931. Three dosage schedules were used at 70* 7.--3-5
lbs/4 hra., 4 lbs/4 hrs., and 3 lbs/5 hrs. Only slight tip injury
resulted, all in the area normally pruned off at planting time.
Your varieties of peach, four of prune, three of sweet cherry,
two of apricot, and two of pear were fumigated in Somerset County, Md.,
late in March 1935. Dosage schedules of 3 lbs/4 hrs., 3.5 lbs/4 hrs.,
and 14 lbs/4 hra. were used, all at 70T 7. Tip injury again occurred,
but was less in comparable treatments than in the Missouri tests.
Three varieties of peach, one of plum, and one of nectarine were
fumigated in Newton County, Mo., on April 4, 1940, with dosage sched-
ules of 3 lbs/4 hrs. at 60* 7. and 2 lbs/4 hrs. at 70e. All trees
were pruned at planting time and all grew normally.
In 1941, lots of 29 varieties of peach, 4 of apricot, 21 of cherry,
11 of pear, 26 of plum, and 6 of ornamental hosts of the oriental fruit
moth were kept under observation following fumigation on January 31
In Pike County, Me. No injury was apparent, and all trees remaining at
the end of the storage period late in April sprouted in a normal manner.
4/ Acknowledgment is made of the considerable assistance given
by members of the State Untomologist's Office, particularly Bert 0.
Brayten, associate entomologist, and J. Carl Dawson, State entomologist
It was concluded from these tests that the dosages used caused
no appreciable injury to nursery trees of stone-fruit, pear, and quince
Tolerance of Nursery Apple Trees
The first tests with apple trees shoved them to be injured with
rhe dosage schedules under consideration at that time. Three varieties
of apple trees were fumigated in Pike County, No,, in January 1935, with
dosage schedules of 3.5 lbs/4 hrs., 4 lbs/4 hrs., and 3 lbs/5 hrs., all
at 700 1. Tip injury was prevalent on all trees, and it was more severe
where the last two schedules were applied. A number of trees failed to
leaf, and eventually died. These amounted to 11, 34, and 24 percent,
respectively, in lots of 110 trees treated with each schedule.
live varieties of apple trees were fumigated later in Somerset
County, Md., in March 19395, with dosage schedules of 3 lbs/4 hrs.,
3.5 lbs/e4 hrs., and 4 lbs/4 hrs., all at T70* 7. In this instance even
greater numbers of trees failed to leaf and eventually died, anounting
to 18, 62, and 55 percent, respectively,
Tests in the spring of 1940 showed that the lower dosage schedules
approved in 1939, of 2 lbs/l4 hrs. at T0 7. and 3 lbs/4 hrs. at 60* Y.,
also caused retardation and death of a number of trees. It was found,
however, that retardation could be prevented by wetting the trees
thoroughly just prior to fumigation. This innovation in procedure was
suggested by nurserymen who objected to an apparent drying of the trees
during the fumigation period. It was accomplished by drenching the
trees with water from a hose or from buckets. In these tests six
varieties of apple trees (Golden Delicious, Jonathan, Rome Beauty,
Starting, Staymared, and. Vinesap) were fumigated on April 2 with a
schedule of 3 lbs/4 hrs. at 600 7. Twenty trees of each variety were
thoroughly wet before fumigation, and a similar number were fumigated
without being wetted., en trees of each 20 were planted the day fol-
lowing; the other 10 were pocked in shipping crates, stored for 2
weeks, then unpacked and plauted. Since there were no differences in
growth between those planted immediately and those packed and stored,
the results are combined. They are given in table 1.
No difference in growth reaction was apparent between lots of
trees fumigated with the two dosage schedules. Six varieties of
apples were fumigated in both Pike and Newton Counties, No., and no
differences in growth resulted. All trees in these tests wore wet
before fumigation. The growth results of the tests in Pike County
are given in table 2.
Table 1.-Growth response of wet apple trees compared with unvetted
trees following fumigation with methyl bromide on Arril 2, 1940
Variety Wet trees Unwetted trees Untreated
Golden Delieious 19 1 13 1 20 1
Jonathan 20 1 13 1 20 I
Rome Beauty s18 11 I 20 1
11 9 D
starking 19 I 7 1 19 1
1D 1 R 1R
Staynared 19 I 18 1 20 1
1 2 D
Vinesap 1s 1 20 D 20 N
Total 1131 62 N 119 N
2 R 1 R
5 D 56 D
Table 2.--Arowth response of apple trees fumiegated with a schedule
of 3 lbs/4l hre. at 60* F. compared with trees fumigated with
2 lbs/4 hr.. at 70'
Variety 3 lbs/4 hr.. 2 lbs/4 hr.. Untreated
,.at 6Oo .at 700 (control)
Golden Delicious 19 1 19 N 19 1
1ID ID ID
Jonathan 20 1 20 1 20 1
ome Beauty 18I 171 20 1
Starkiag 19 1 20 I 20 1
Staiyared 19 19 1 20 I
Vinesap 18 I 19 I 20 I
Total 113 I 114 lI 119 I
I 6 D ID
I normal growth.
R a Retaried growth.
D n Dead.
In studies nade during the winter and spring of 1940-.41 it was
shown that retardation vas greatest following treatments in March and
April. In these tests the practice of vetting trees prior to funigatiean
was again shows to be of distinct benefit in preventing retardation.
smltgation and restorage of trees in early winter or midwinter was
shown to be practisole. In these tests three apple varieties wero used
which had shown the greatest retardation in trees not vetted in the
tests in 1940. Lots were fumigated in Pike County, Me.. at four dates
during the storage period -December 18, January 31, March 21, aM
April 23. On each date vet trees and trees not wetted were fumigate#
with the sohedules at both 600 and 70* 7. Appropriate controls vere
kept with each lot. The results are given in table 3. eOw trees were
retarded in lots treated December 18 or January 31, but the numbers
increased considerably in the March 21 and April 23 lots, as showa
in the following svnmary of the number of trees dead or unfollated
at the end of the growing season:
December 18 January 31 March 21
The few retarded trees in the December and January lots indicated
the retardation was associated with the spring treatments. Of
trees that died in the lots treated in March and April, 14 were
trees and 30 not wetted, which indicated that wetting prevented
some trees at that season.
Table 3.--Growth response of trees fumigated
throughout the winter storage season
at various dates
Treatment Treated Treated Treated Treated
Peo. 18 Jan. 31. NMar. 21 Aw. 23
3 lbs/60 wet
3 lbs/600 -unwetted
lot treated (check)
2 lbs/70To wet
2 lbs/70 unwetted
Not treated (check)
Total of treated
3 lbs/60 vet
Not treated (check)
2 Iba/TO* wet
2 lbe/70 unwetted
Not treated (check)
Total of treated
3 lbs/60 wet
3 lbe/60 unwetted
Not treated (check)
2 lbe/70" vet
2 lbs/70* unvetted
lot treated (check)
Total of treated
NI Normal growth.
R Retarded growth.
D a Dead.
Following the discovery that the retardation of fumigated trees
vas associated with treatment in the spring season, all the previous
work was reviewed. The Maryland tests in 1938 and Missouri tests in
1940 had been made in March or April. The Missouri tests in 1938
had been made late in January, but with higher dosage schedules. In
all instances death of a considerable number of trees resulted. Fur-
thermore, it was noted that two types of injury, apparently unrelated,
had been recorded, (1) a primary injury confined to tip wood, which
appeared soon after fumigation, and (2) a retardation of growth.
The tip injury resulted in the death of the affected portion and
apparently did not advance beyond the initial injured area. It was not
distinguishable from other tip injury due to storage factors, but it
was well shown to have booeen a result of fumigation in the treatments
of 1938, in which the average length of injured tips increased in
proportion to an increase in dosage schedule.
Retardation, on the other hand, was not noticeable until the
normal trees started leafing. Retarded trees were divided into two
groups -- those that leafed out belatedly and soon appeared normal
and those that remained leafless. The leafless trees remained alive,
as evidenced by the condition of the cambium, until midsummer or later.
Occasionally retarded trees appeared in the controls and reacted in
the same manner as retarded treated trees.
Since the retardation was distinctly different from the primary
injury as evidenced by tip injury, it was concluded that it was caused
by drying of the trees during the fumigation operation. Trees are
Ianown to be much more susceptible to drying when breaking from dor.-
sancy, than when fully dormant, hence the greater amount of retarda-
tion that followed spring fumigations was to be expected. The
beneficial effect of wetting the trees prior to fumigation during the
spring treatments was thus explained.
This point was demonstrated in 1942 in tests at Beltsville, Ud.,
with nursery trees of the variety Winesap fumigated on April 13.
Groups of 11 trees each were fumigated (1) after wetting without
wrapping, (2) without vetting but wrapped, wholly or partly, with wet
burlap and straw, or (3) without either wetting er wrapping. Their
reactions were compared with those of similar groups receiving no
fumigation but held normally or exposed to a period of drying.
The results were as follows:
All wetted Wholly Roots Tops ]either Control, Control,
but not wrapped wrapped wrapped vetted normal dry
wrapped but not but not but not nor
vetted vetted vetted wrapped
11 1 10 1 10 I 61 7 1 9 2 1
1R 1R 4R 2R 11R L
1U 2U 1 U 5
X a normal, BR retarded, U = unfoliatedo.
Unfusigated trees which were exposed to drying conditions made a
poorer growth response than trees in all fuaigated lots, and the reac-
tion and appearance of retarded and unfdiated individual trees were
identical with those of retarded or unfoliated. trees in the fumigated
lots. ?rees vet. wholly protected, or with roots protected made the
best response, whereas those not wetted and those with the roots or the
whole trees unprotected shoved nore retardation.
?rom these tests it was concluded that nursery apple trees coult
be successfully fumigated with dosages of 3 lbs/4 hrs. at 600, or
2 lbs/4 hrs. at 70" F., provided that the trees were fumigated early
in winter or during midwinter, or that all trees were thoroughly wet
Iquipment and MKethods of Procedure for Commercial Use
A standard design for the fumigation vaults was desired so that
approval of individual units by the Western Plant Board would not be
oomplicated. Therefore a design already in use by the Bureau for
other purposes was adapted. In this design each unit was lined with
shooeet metal and the doors and other openings were tightly fitted
against molded sponge-rubber gaskets. A combination circulating and
exhausting system was provided by a motor-driven blower and a vent
which, when open, diverted the gas into the exhaust duct. Provtoiir
for heating was required so that the temperature could be maintained
at 60e or 70" 7. as desired. The insulation of the walls was optional.
An adequate duct system to carry the exhausted gas to the outside was
also necessary. This design is shown in figure 1.
The fumigation vSults were built by the nursery companies under
supervision of their State nursery inspectors. Sizes rarner fr-B
150 to 1,600 cubic fooeet (figs. 2, 3, and 4). In larger ..its the
trees were loaded on trailers, which were roiled in atnD o.1t of te
fumigation vault (fig. 5). In some eastern States :;4 'rviIt
already approved under the Japanese beetle quarantine w uned since
they also conformed to the basic design.
The first fumigation of trees by nursery companies was made con#-
currently with the earlier experimental studies, in 1938-39, when
10,983 trees were fumigated and certified for shipment in Missouri.
In 1939-40 the number of trees increased to 56,554. In 19O40-41 and
1941-42 totals of 137,171 and 111,850 trees were fumigated in Missouri
alone, and shipments were also made from Ohio, New York, New Jersey,
Maryland, Arkansas, Iowa, Kansas, and probably other States.
Based on early experimental studies, fumigation generally excluded
apple trees, but by 1942 the numbers of apple trees treated had in-
In commercial practice the trees are assembled and thoroughly wet
down before being placed in the fumigation vault. The: may be laid
on racks in the vault (fig. 3), or loaded on trailers (fig. 5) which
are rolled into the vault. The bulb of the thermometer unit is placed
in the center of a bundle of tree roots at the densest point. When
the temperature at this point reaches the desired level of 60O or
70* 7., the fumigant is introduced. The blower is operated throughout
the 4-hour period. At the end of the fumigation period the vault is
ventilated and the trees are removed.
Where moderate quantities of trees are to be treated, they are
usually assembled as orders and fumigated Just prior to shipment.
Where large numbers are involved, stocks of many varieties are fumigated
and stored in special bins, and orders are filled from these bins.
Studies of the reaction of dormant nursery trees to fumigation
schedules for methyl bromide under the requirements of the oriental
fruit moth quarantines of various States were made concurrently with
studies of larval mortality, which have been reported elsewhere.
Stone-fruit, pear, and quince varieties showed no appreciable injury
from fumigation schedules in tests made at various times from 1937 to 1941l
Nursery apple trees were injured and their growth retarded in tests
with high dosage schedules under early quarantine requirements. In later
tests with lower dosage schedules it was shown that retardation was
greatest following fumigations in March and April, and that wetting trees
prior to fumigation prevented, to a large extent, any serious retarda-
tion. Tip injury did not occur to any extent with these newer, lover
It was further found that this growth retardation after fumigation,
which occurred more frequently as spring advanced, was indistinguishable
from retardation caused when trees are dried by exposure during the
period when they break from dormancy. It was concluded, therefore, that
such retardation following fumigation treatments was du to the drying
of, the nursery trees during the fumigation process. This explained
the beneficial effect of vwetting the trees prior to fumigation during
the spring period,
A standard design of fumigation vault was adapted from one
already used for other purposees, and a number of vaults were built
by nursery companies, in which thousands of tree were fumigated and
shipped under quarantine regulations*
Figure 1.-Design of approved type of methyl bromide fumiation
Figure 2.-Small type of nursery stock fumigation vault
of 150 cubic feet capacity.
Figure 3.--Intermediate size of nursery stock fumigation
vault of 500 cubic feet capacity.
UNIVERSITY OF FLORIDA
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Figure 4.--Large type of nursery stock fumigation vault
of 1.600 cubic feet capacity.
Figure 5.--Trailer load of nursery trees being moved
into a large fumigation vault.