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varieties a spray application may precede the harvest date by considerably
longer periods than is the case with Mcintosh. For instance, the effect
with Winesap has persisted longer than 4 weeks from the date of spraying.
However, with all varieties there is a time limit beyond which effectiveness
decreases markedly. With Mcintosh and Wealthy this interval seems to
be peculiarly short.

Effect of a Single Late Application

It is possible, of course, to apply hormone sprays at any time after drop-
ping has begun. Common sense, however, imposes certain limits. For
instance, since the effect from an application will not be manifest for from
2 to 4 days, there obviously would be little justification for spraying trees
which are to be picked within 4 or 5 days. Furthermore, as the proportion
of a crop which has dropped increases, the probability of an economical
use of hormone sprays decreases. Finally, a point is reached where an
application is not justified.

It has been stated that a spray should go on very soon after dropping
has commenced in some volume. But suppose that a grower, for some
reason or other, fails to pick or to spray a block until one day he observes
that perhaps one-third of the crop is on the ground? Furthermore, he
figures that he will not be able to pick the block for another week. Will
hormone sprays be helpful? This question cannot be answered categorical-
ly because no two situations are strictly comparable. Table 3 illustrates
what happened in one such case in an experimental block at Massachusetts
State College.

Table 3. — Average Cumulative Percent Drop of Original Crop.
(Sprayed September 28 — Harvested October 7)

Test Hormone
p. p.m.




Average Calculated

Number of Bushels

Apples per Acre

Per Tree Dropping

After Oct. 1









4 (a) 10












4 (b) 10













This test (Number 4) is separated into two parts: (a) young trees,
(b) mature trees. It is interesting to note the similarity of results. The
spray, which included one pint of oil per 100 gallons, was applied on Sep-
tember 28. The effect is barely discernible in the table on October 2 and
becomes progressively more pronounced up to the time of harvest. It


should be noted that the average dropping percentages of the sprayed and
the check trees in each case were practically equivalent up to October 2.
Although the actual yields are not the same, estimates of the drops per
acre based on these yields are given. Under conditions of these tests, a
saving of about 50 bushels per acre could be attributed to the late hormone
spraying. These estimates are based on 27 trees to the acre for the large
trees and 50 trees to the acre for the smaller ones. Of course this arbitrary
analysis is for comparative purposes only. No two tests could be expected
to give identical net results. Thus, if the above yields had been higher, the
benefit froin spraying would have been enhanced.

Two other tests were conducted where spraying was delayed even longer
than in the above cases. There was some effect from these applications,
but the results probably did not justify the cash outlay and the time ex-
pended. Furthermore, the data indicate that the effectiveness of a hormone
spray application on Mcintosh may be progressively less pronounced as
the crop becomes more and more mature on the tree. Involved, of course,
is the question of decreasing temperature means as the season progresses.
Late spraying of York Imperial and Rome Beauty in Maryland (1), Bald-
win in Rhode Island (5), and Baldwin at Ainherst was generally unsuccess-
ful in lessening subsequent dropping. This possibly may be explained on
the basis of the low physiological activity of the tissues of the tree late in
the fall. Without ignoring the question of variety itself, the above argu-
ment is supported by the fact that early apples usually are more likely to
react favorably to hormone applications than late varieties.

It is a widely accepted fact that losses from preharvest dropping of Mc-
intosh were, in general, less pronounced in 1940 than in many previous
years. This was certainly true in Massachusetts. As a result, several
investigators have concluded that the response of Mcintosh to hormone
sprays in 1940 may not represent a true index of response for a normal sea-
son. August and September were relatively cold months, the Amherst
mean temperatures being respectiveh^ 1.7° F. and 1.6° F. below normal.
That the effectiveness of the hormone in a spray is influenced greatly by
differences in temperatures at a critical time has not been proved, but may
offer one explanation for certain differential results. It has been observed
that high temperatures at this season increase preharvest dropping of
apples. This is discussed at greater length in a previous publication (6).
It is sufficient here to emphasize the important influences which temper-
ature may have on drop. With high temperatures, which favor dropping,
the usefulness of hormone spraj's may be enhanced.

Effect of Concentration

The amount of active hormone in the spray solution seems to be very
important. The proprietary commercial hormone preparations on the
market last season were designed to furnish 10 parts of hormone per mil-
lion parts of water when the manufacturer's recommendations were fol-
lowed. This is a .001 percent concentration. Table 4 summarizes results
secured as a result of reducing the hormone concentration. Three com-
mercial preparations were used. In every case, some decrease in effective-
ness resulted from the use of the lower hormone concentrations.

This finding is substantiated, in general, by results elsewhere. Gardner,



Marth, and Batjer (2) in tlieir first full rei)ort in 1939 stated that with
Mcintosh ". . . . as with other varieties, the higher concentrations have
given better control within the effective period." Some further work
(1940) by Batjer and Marth (1) supports this statement, especially in re-
gard to late varieties. However, with some varieties, particularly Williams
Early Red (1) and Mcintosh', drop control was not necessarily improved
by increasing the hormone concentration above 5 p. p.m. Also, Murphy (5)
in Rhode Island found no significant differences in the drop of Mcintosh
from trees receiving sprays with different hormone concentration. Consid-
erable variability was evident within treatments. The results of Hoffman
(3) in New York with Mcintosh suggest that the standard .001 percent
sprays were possibly a little more reliable than sprays with half the amount
of hormone. Murneek (4) found more reduction in amount of dropping
of Delicious with a .001 than with a .0005 percent spra\'. Other experi-
ments seem to present a further picture of variability in results. However,
the evidence on the whole seems to verifj' the authors' experience that the
higher concentrations up to 10 p. p.m. are usually somewhat more effective
in controlling preharvest drop. A test (Mcintosh) in Canada^ resulted
in better control with about 15 p. p.m. of hormone than with the standard
10 p. p.m. spray. In a single test with Baldwin at Amherst, a sim-
ilar high concentration seemed to increase effectiveness. But most of the
sprays contained 10 p. p.m. or less of actual hormone. Table 4 gives some
results with Mcintosh and Wealthy.

Table 4. — Percentage of Total Crop That Dropped After Treatments
Became Efft:ctive in Several Tests.










Number of




per Tree



Sept. 13

Oct. 2






Sept. 1-1

Oct. 2


(-1- oil)




1/2 (+ oil)





Sept. 13

Sept. 23










Sept. 4

Sept. 20








Sept. 4

Sept. 19







'L. P. Batjer. Correspondence. 1941.
^G. H. Dickson. Correspondence. 1940.


The data in Table 4 do not show uniformly good results from spray
applications (note test 1) and few of the differences in ])ercentages of
drop due to hormone concentration are large enough to be significant.
Whether any of the differences are sufficiently pronounced to justify the
use of the stronger sprays is a inatter of opinion. For example, let us
briefly analyze test 2. The average tree yield of the block was 20.1
bushels. This average is used rather than the actual yields because of the
large variations in the latter. Since higher percentages of drop often
have been found to be associated with heavy production (6), the calcula-
tions herewith tend to be conservative. That is, the check trees rather
than the treated trees are favored because the lower yielding trees (this
particular season) were chosen for the check trees. Now, on the basis
of 27 trees to the acre, the bushels dropped per treatment per acre were
as follows: 10 p. p.m., 68.3; 2'/ p.p.m., 89.8; check, 131.8. In short, the
weak spray application saved 42 and the strong 63.5 bushels. The dif-
ference is 21.5 bushels of Mcintosh apples per acre. The costs of applica-
tion were the same except for the diflference in the amount of hormone
material used. Assuming a figure of 1.5 cents per gallon of spray as the
actual cost of the hormone, this item of cost per acre based on 30 gallons
per tree was $12.15 for the stronger spray and $3.04 for the weak spray,
making a saving of $9.11 per acre in the case of the latter. The problem
is resolved to the question of the economics of spending $9.11 to save
21.5 bushels — approximately 42 cents per bushel. This analysis considers
the problem only in terms of the actual bushels of apples saved. There are
other considerations which should not be ignored, however, such as the
increased development of quality; the nature of the surface on which the
drops would fall, which largely determines injury to and hence the salabil-
ity of dropped Mcintosh; and the local market situation in relation to
disposal of such drops. A limited supply of good "drops"may find a ready
market. Usually, the average market price for such apples, however,
ranges from 50 cents to one dollar below that of hand-picked Mcintosh
out of cold storage.

Such an analysis could be made of each test in Table 4. In tests 1 and
5, the increased dollar value of the strong over the weaker sprays is much
less pronounced than in test 2. With Wealthy (tests 6 and 7) the added
effectiveness of the stronger sprays is evident and their use might seem
justified on the basis of these tests. However, the varietal problem
enters the picture here. For many Massachusetts growers it may never
he profitable to spray Wealthy and some other "before Mcintosh" sorts
due to a characteristic downward trend in the price level for such varieties
as the season progresses. Even with the very eflfective control of drop-
ping that was obtained with Duchess, it is doubtful that hormone spray-
ing can be economically justified with such a variety.

Thoroughness of Application

As with spra3dng for disease and insect control, hormone spraying for
drop control is dependent for effectiveness upon good coverage. Best
results have been obtained when sufficient spray was applied to "wet"
the entire tree thoroughly. The most eflfective part of an application has
seemed to be the spray that hits and wets the fruit stems. Theoretically,


for best control, the hormone should come in contact with the abscission
zone itself. This is the area that roughly defines the location of the
abscission layer which, upon development, separates the pedicel from the
cluster base (the stem from the spur). Gardner, Marth, and Batjer (2)
have reported some eflFect from a spray applied only to the calyx end of
Delicious fruits. But such an eflfect must be of doubtful significance.
They also found that leaf coverage is not particularly important. Apples
only a short distance away from sprayed foliage seem to be aflfected little
if at all.

The amount of spray material which is adequate for thorough coverage
depends on a number of factors such as wind movement, spray pressure,
and especially spraying technique. Material, of course, should be applied
efficiently with a minimum of wastage, but it is better for best control of
drop to apply too much than too little. Reports of amounts used in 1940
vary remarkably. In some cases, good results evidently were secured
with young trees when less than 5 gallons of spray were used per tree.
Another extreme was the application of more than 40 gallons on single
trees. These, of course, were very large trees bearing 15 to 40 bushels
of apples. Two ways of determining the amount of spray material needed
are based respectively on tree size and on tree crop. Competent men on
a spray rig will automatically consider both aspects. With hormone
spraying it is the apple rather than the leaf that deserves primary con-
sideration and this fact naturally places emphasis on the crop of fruit
rather than on the size of tree. On this basis, a recommended application
might be from one to two gallons of spray for each estimated bushel of
apples. Results have been too inconsistent and individual situations are
too variable to allow a more specific recommendation. The important
point is that very thorough coverage is essential. For example, in Mary-
land (1), with Delicious averaging seven bushels per tree, a 5-gallon
application per tree was just one-half as effective in retarding drop as a
10-gallon application of the same strength.

This brings up the possible use of dust in a drop control program.
Several advantages of dusting over spraying are obvious to those who
have used both systems. One of the most important considerations is
the shorter time required for dusting. Since hormone spraying comes
during a particularly busy season, the time required to put on an applica-
tion is of vital concern to growers. Hence, the question of incorporating
the hormone in a dust carrier for use in the usual orchard dusters has
been raised. Although the efficacy of this method of hormone application
to fruit trees is practically unknown, it is believed that dusting will not
eflfect as thorough coverage as spraying. Intimate contact with tissue
.surface is better obtained with a wet than with a dry film of material.
The question is further complicated by the fact that, to be most effective,
the hormone probably should be in solution, although for certain other
uses dust application of hormones has been quite effective. The possibil-
ities of hormone dusts are being investigated further and it is possible
that certain of the obvious difficulties may be remedied, .^t the moment,
however, since spraying itself is none too effective, partly because of in-
adequate coverage, a dust program for drop control ofifers little encourage-
ment, especially with Mcintosh.


Addition of Oil

III 1939, tiardiicr, Martli, and Batjer (2) reported increased effectiveness
ot drop control sprays when a small amount of oil was added. Since it
seemed that even a small quantity of oil might act as a spreader and
improve coverage, it was included in some tests with Mcintosh. The
addition of a summer oil (1 pint per 100 gallons) had an effect similar to
that reported above. For example in one test, using 10 p. p.m. of hormone,
tlie dropping amounted to 10.2 and 14.1 percent respectively witli and
witliout oil. Tlie check trees dropped 24.3 percent. Furtlier work nui\
indicate that the use of oil may compensate in part for decreased hormone
concentrations. At the present time, however, it should be considered as
a supplementary procedure to enhance the action of the hormones. Its
use should not affect apples in appearance, quality, or storage ability.

Importance of Size of Crop

It lias already l)een suggested that the amount of fruit on a tree may be
a deciding factor in determining the advisability of using a hormone spray
It) lessen dropping. The grower is interested in actual bushels, not in
mere percentages. Percentage figures in themselves, as related to dropped
aijples, mean little in terms of monetary gains or losses. However, when
a grower reads that a hormone spray has reduced drop by 10 percent, he
immediately associates this percentage figure with an arbitrary orchard or
acre yield, or possibly with the known performance of his own trees. The
"10 ])ercent" then becomes "bushels per tree" or "bushels per acre" and
lias a definite meaning so far as that grower is concerned. Other growers
will interpret differently as a result of different yield standards. Thus,
with a 200-bushel yield per acre, a reduction in drop from 15 to 5 percent
means a saving of 20 bushels. Such a reduction with a 600-bushel yieUl,
on tiie other hand, gives a saving of 60 bushels per acre — an increased
saving of 40 bushels. Hence, it is evident that size of crop is especially
significant in the economical use of hormone sprays. The heavier the
\ield, tlie more jiistification there is for a hormone application.

Orchard Variability

.Since the purcliase of liormones and their application cost considerable
money, it is wise for each grower to consider carefully to what extent
this method of decreasing drop should be utilized under iiis particular
conditions. No two Mcintosh orchards are alike. Even similar appear-
ing orchards in close proximity often behave differently in regard to pre-
liarvest dropping of fruit. This same variability may e.xist among neigh-
boring trees in a single block. It has been shown also that severity ol
droj) with Mcintosh may be associated with a high state of fertility,
esijecially in relation to nitrogen. These relationships have been discussed
fully in a previous publication (6). Briefly, when available nitrogen is
jjlentiful and trees are in a vigorous state of growth, more severe pre-
harvcst dropping of apples is likely to occur than when trees are grown
on the "liard side." Since good vigor is essential for high production, a
method to reduce premature dropping other than by decreasing vigor is
ol paramount significance. The use of drop-control sprays is especially


adapted to sucli a setup. Past records of drop sliould enable growers to
choose the particular orchards that have caused the most trouble with
excessive fruit drop year in and year out. These should have precedence
in receiving hormone sprays over orchards whicii have a record of pro-
ducing fruit that attains good size, color, and maturity before falling to
the ground.

Experiment with Excised Branches

Two similar branches of a Mcintosh tree were chosen for a comparative
study of fruit drop following their removal from the tree. One was
sprayed thoroughly on September 18 with a hand pressure sprayer using
a spray containing 20 p. p.m. of naphthalene acetic acid. The other branch
served as a check. On September 22 the two branches were carefully
removed from the tree and the cut ends were placed in water. The
branches were supported so that their previous positions relative to the
horizontal were approximately maintained. There was some dropping
of apples within a few days from the unsprayed branch, and apples con-
tinued to absciss until all (23j had dropped. The hormone-treated branch,
however, showed practically no dropping of its 36 apples for longer than
two weeks. Even a month later, after two freezes, some apples were still
hanging. Previous work (6) has indicated that an injured limb may
exhibit delayed dropping of fruit to some degree and possibly these
branches so behaved. However, the effect from the spraying was far
more significant than the effect from the cutting itself.


'iiie use iii so-called hormone or drop-control spra\s to tlecrease the
preharvest dropping of apples offers some promise to fruit growers in
Massachusetts. The method is still in the development state and the
material in thi.s bulletin sums up much of the present knowledge concern-
ing it. Some aspects are more definitely established than others where
results have not been sufficiently extensive or uniform for positive con-
clusions. That certain chemicals, such as naphthalene acetic acid and
naphthalene acetamide, when dissolved and diluted in water and applied
to apple trees around harvest time, exert a retarding effect on natural
fruit drop is well authenticated.

There is no doubt also that the effect of these and other chemicals is
variable. Many factors may contribute to this variability, such as variety,
time of application, thoroughness of application, concentration, weather
conditions, and season. These factors and other considerations iiave
been discussed and the attempt has been inade to evaluate their signif-
icance on the basis of exjjeriniental tests. Most of the work was done
with Mcintosh.

The effective period of hormone spra\'s is tiie number of da\-s that a
retarding influence on drop is maintained and varies greatl\' with variet\ .
With MclntoNh and Wealthy this period was about 10 to 12 da.\s. With
other varieties, it is usually somewhat longer.

The practical effect of a S];ray application is not immediately apparent.
L'sually from two to three da\'s elapse before dropping is measurably


retarded. The interval between application and elTect may be longer if
the temperature is relatively cool.

The response of dififerent varieties is variable. Drop control was most
successful with Duchess of Oldenburg and an unknown earlj- fall variety,
and least successful with Baldwin. Control was variable with Mcintosh
and Wealthy. Reports from tests in other states show that early varieties
in general responded better to hormone sprays than later varieties, al-
though there were exceptions.

The application of hormone sprays must be timed accurately for best
results, especially with Mcintosh. As soon as well-sized and uninjured
uiiilorm apples begin to drop in any quantity, a spray should be applied.

Most repeat sprays were unsatisfactorj'. A single application, well
timed, should furnish the most economical protection.

The longer an application is delayed after dropping hag commenced,
the less opportunity there is for benefit from a commercial standpoint.

The concentration of hormone in the spray had a decided influence on
the degree of drop control. Better results were secured as the amounts
of chemical were increased up to 10 parts per million of water. Whether
increased effectiveness warrants the extra cost for material is not definite.
A{ the moment it seems unwise to use tiie lower concentrations with
Mcintosh. Whether higher concentrations than 10 p. p.m. might be justi-
lied lias not \'et been shown.

It is essential to wet eacii apple stem for best control of preharvest drop.
This means very thorough coverage — 10 to 40 gallons per tree or 1 to 2
gallons i)er bushel oi fruit. Dusting does not seem feasible at the present

The inclusion of a small amount of summer oil tended to increase effec-
tiveness. One pint in 100 gallons of spray did not seem to affect the fruit
in any way.

The temperature before and during the normal harvest season may be
very important. Warm weather seems to have an accelerating effect on
fruit abscission. Cool weather delays fruit drop. It is possible that hor-
mone spraying is more effective in warm weather.

There is no evidence that would indicate any harmful effects from the
proper use of hormone sprays on the fruit, on the tree, or on consumers.

It is probably to the growers' advantage to use the commercial prepara-
tions. There is not sufficient evidence at the present time to permit the
recommendation of one commercial product more than another.

In Massachusetts any extensive use of hormone sprays will be limited

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