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INVESTIGATIONS ON THE RELATION

BETWEEN LEAF AREA AND
SIZE OF PEACHES

Thesis for degree of M. S.

William Crippen.§ggwn
19.3.5

Submitted to the Faculty of the Michigan State
College of Agriculture and Applied Sci-

ence in partial fulfilment of the

requirements for the degree

or Master of Science.

a: i 5/fl472d, /735 “
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1H E513

 

 

Introduction

Commercial peach.growers realize that
the price for peaches depends in no small
measure upon the size. Large fruits will
bring better returns to the producer than
small ones. many factors influence the size
of peaches, such as soil, rainfall, climatic
conditions and the relative load the trees
carry. This latter factor is under the
control of the grower, and for many years
peach growers have practiced the removal
-of surplus fruits in striving to produce
a better grade of marketable product.

9913-}

Review of Literature

Section I. Fruit Removal, Pruning and.Fertilizers
5; Factors which Influence the size of Peach Fruits.
During the past 35 years there have been.a number of
studies for the purpose of establishing definite
methods and affording more or less fixed rules that
could be successfully followed in thinning peaches.
Early investigators recommended thinning peaches to
some arbitrary distance apart on the branches.

The}! (1). (2). (8). (ll). (12). (29). (30). (31).
(32), (27, and (57), agreed that thinning should
not be done until after the "June drop".s Jordan
(27) in 1898 wrote cn"Pruning and Thinning" of
peaches: ” These operations exercise _a great
influence on the life of the tree and the size and
the color of fruit. .Thinning is not practiced to
the extent that it deservee.for direct experiments
drenwanting, the fact remains that the removal

of one third or one half of the number of fruits
on the tree, as the occasion demands, greatly in-
creases the size and quality of the remaining
fruits. Thinning is secured in two ways either

by hand picking all the small imperfect fruit and

sufficient number of the remainder to leave none

closer than three or four inches (this is best
done after what is called "June drop" occurs),

or annual cutting off with pruning shears at
regular time of trimming from a quarter to half
as required of each years growth. The first met-
bed is best."

Close, (10) wrote in 1902: "The thinning
of peaches is not practiced in Delaware to the
extent that it should be. Where thinning was
undertaken, there has been an influence which
has caused the thinned trees to set a good
load of uniformly distributed fruit, while
adjoining unthinned trees set either an ex-
cessively heavy load or awery light load.

The points in favor of thinning are an even dis-
tribution of fruit on the tree, larger size,
brighter color, better quality and flavor, more
fancy fruits which are first class, less culls,
higher prices, and the trees are in better con-
dition for a crop the following year. 'Common'
thinning four inches. 'Medium' six inches, and
'Severe' eight inches apart. were used in the
thinning tests. Unthinned Elberta trees gave

forty eight per cent fancy, and forty nine
per cent first grade fruit, and the thinned

tree produced eighty per cent fancy, and twenty per

cent first grade."

Walker (36) writing on peach growing in Arkansas
says: "Some effective thinning is done at the time
of pruning the tree each spring, but this is not
sufficient. The best practice requires that the
peaches on the limb shall not be closer than.four
to six inches. Thinning increases the size of the
remaining fruit and is a saving of strength to a
tree in reducing the number of pits borne.”

Barden.and Eustace (l) in 1913 wrote: "The

best results are obtained by thinning peach var-
ieties in order of ripening. Various rules are
sometimes given as to the distance apart to leave
the fruits, but they should be regarded as very
elastic. varieties that are inclined to bear heavily
and that ordinarily produce small fruit must be thin-
ned severely. If a tree has.one part full and the 0th
other light the heavier portion may be thinned less
than it would be if the whole.tree were full. Trees
that are for any reason regarded as 'weak' should
not be allowed to bear heavily. If a tree has been
well pruned the fruits may be left nearer together upon
the twigs than would be permissable with poor pruning.

It must be remembered that the production of peach

pulp does not draw heavily upon the tree, but it is
the formation of pits and seeds that taxes the vit-
ality. Hence, the most pulp that can be produced
per tree, with the smallest number of pits possible
will not only give the most economical production
per tree but better fruits for the market. Care
should be taken in thinning to remove all of the
inferior or injured specimens. The earlier the
thinning is done after it can‘be determined which
are the permanent fruits the better will be the
results. The size of the remaining fruits will be
increased when the thinning is done late, but it
will be far less beneficial to the trees." They (2)
state: "The financial record of twelve years of a
fifteen acre orchard will be of value and interest.
The total cost of thinning for the twelve years was
$154.30. There was no thinning the first three
years and the eleventh and twelfth. The total cost
of orchard expense was $ 7,851.37. Two percent of
the orchard expense was thinning. The total pro-

duction was 16,972 bushels. Therefore the cost of

thinning was approximately one cent per bushel."

Gardner, Bradford and Hooker (21) 1927, in

their book "Orcharding", say:"Actual count showed
an eight year old unpruned peach.tree to have 37,582
fruit buds. many factors operate to reduce greatly
the number of fruits that a tree actually matures,
below that which theoretically is provided for by
its fruit buds. In.this particular case bud killing
amounted to approximately thirty per cent and only
one fifth of the blossoms set fruit, This tree actu-
ally matured l,213 fruits that averaged slightly
under two inches in diameter and slightly over two
ounces in weight, and numbered about two hundred and
seventy five to the bushel."

Gardner, Mhrshall and Hootman (22) studied the
relationship between size of peaches and size of crop-
Some of the results of their investigation are: ”Two
principal cultural practices, pruning and thinning,
are used to produce large fruits. Also, soil fertility
is generally recognized as an important factor affecting
the vigor and productivity of peach trees. Experiments
have demonstrated the value of nitrogenous fertilizers
in.the peach orchard, and many growers have found that
these applications have paid good dividends. At current

prices for the different sizes and assumed average cost

per tree of ten cents for material and labor of applicaéign

tion, fertilization increased the return from each

unpruned tree from $1.59 to $3.09 in 1924." The
following two years similar investments in.fertil-
izer increased the returns on thinned and unthinned
peach trees. The experiment indicates that generally
fertilizer applications yield larger retunns on ligh-
ter soils with old trees, than with more vigorous
trees.

”Experimental tests were made on the influences
of pruning on sheet lenght and size of peaches. It will
be noted that the pruning that was afforded resulted
in practically doubling the average shoot length and
the average number of buds per shoot. The buds on the
longer shoots were also more susceptible to frost inj-
ury and indicated clearly that severe pruning is of
doubtful benefit from the standpoint of increasing the
bearing surface. On the other hand it affects the
distribution of the bearing wood making it more vigor-
ous in.the center of the tree. The importance of this
latter influence is usually underestimated in.the case
of the peach, whose wood breaks easily and whose crutches
split so easily. Some of the pruning treatments resul-
ted in slightly increased returns and others in slightly
decreased returns. However it will be noted that half
of the crop borneby unpruned trees was without commer-

cial value. The tree appearance Justified the pruning

process by keeping the trees within reasonable bounds

and thereby reducing vigorous production costs.

"Thinning of friut is regularly employed as a
means of improving grade. Thinning experiments were
carried out in three orchards. An attempt was made
in the thinned plots to remove enough surplus fruit
so that no two remaining fruits would touch each
other and in most instances they were thinned so as
to be about four or five inches apart. The thinning
was done comparatively early in the season to give
the fruits which remained the greatest possible op-
portunity to profit by the removal of their compet-
itors.“ .

”Results that were obtained in 1926. In most
instances thinning resulted in a reduction in.total
yield, in one plot this reduction amounted to forty
seven per cent. Where comparatively light thinning
was practiced on heavily loaded trees, however,there
was no reduction in total yield and in one instance
a slight increase. Thinning invariably resulted in
an increase in the percentage of large fruits and in
most instances in an increase in absolute amount of
the larger sizes. The data indicate that the amount
of the increase in the size of fruit is determined
by the number of fruits borne by the tree during the

later part of the growing season rather hhan‘by the
percentage of the fruits removed in the process of
thinning, because no close relationship is evident
between.the degree or the severity of thinning and
the increase in the size of fruits. This statement
is supported by the fact that an unthinned tree
carrying two thousand fruits may be expected to
produce fruit of the same average size as one of
equal vigor with 4,000 fruits of which half are
removed in early summer. The practice of thinning
fruits so that certain arbitrary distances exist
between those that remain is sound. Fruit thinning
resulted in decreased net returns per tree in those
instances where the total yield was materially re-
duced, but, where the thinning was less severeaand
yield remained approximately the same, returns were
increased. .

”In the Elberta orchard near Berrien Springs in
1926, fertilized and moderately pruned but unthinned
trees averaged 2.8 bushelsceaeh and it required an
average of 189 peaches to make a bushel. Correspond-
ing trees whose fruit was moderately thinned averaged ‘
2.4 bushels each and it reouired 169 to make a bushel.
In 1927, the same group of trees averaged four and

three tenths bushels, respectively. The thinned fruit

10

sold at a premium of thirty cents per bushel in
1926, Just compensating the grower for the reduc-
tion in yield. In 1927, there was a slightly
greater difference in the price between the two
sizes, the general price rangecwas higher, the
trees yielded more heavily, and fruit thinning
resulted in a net profit of about twenty five
cents per tree. Therefore moderate thinning of
fruit resulted in increased size and greater re-

turns per tree when.the trees have set a heavy

crope'

Section II. The Rate and manner of Fruit Growth

as Related to the Size of Peach Fruits. During

the past twenty years some studies have been made

of the physiological factors influencing the growth
of peaches. In 1905 Biglow and Gore (3) studied
the chemical composition of the peach during its
different stages of deveIOpment. In 1914 Blake and
Connors (7) studied the causes of the EJune Drop" of
peaches. They wrote: "This shedding of falling of
fruit has been largely attributed to such factors as
a lack of pollination, and insect and disease attacks.
If eggs of plum curculio hatch and infest the fruit

it is certain to fall and severe feeding punctures

11

by the same insect near the stem of the fruit may
produce a similar effect.

"The cause for these fruits being small and
their failureto develop has been attrubuted to the
lack of pollination in most instances. This does
not appear to be true, however, from observations
and studies at the New Jersey experiment station.

It has been noted that these small fruits have
developed from smaller fruit buds upon the twigs.
The work of Huber shows that the pollen in.those
smaller buds which, also bloom later than.the larger
buds,is Just as viable at that of the larger buds
except in instances where the twig, is greatlydde-
ficient in'vigor and it appears certain that as
perfect pollination occurs with the smaller buds

as with the larger. It is also known that the peach
is self fertile. During cold wet weather at blooming
time the fruit may fail to set upon the peach from
the lack of pollen, but, this is not believed to be
the common cause of the small fruits which fall.‘I

Blake (4) in 1919 made growth measurements of
various varieties of peaches to determine the period
at which growth takes place. Measurements were made
weekly, starting three and one halfweeks after blos-

soming. Average fruits were selected and measurements

12

made in the widest median axis. The measurements

-were as follows :

Date May June June June ‘ June July
29 5 12 19 26 2

Eflberta 1.18” 1.55" 1.44" 1.48" 1.50" 1.51”

Hale 1.36" 1.55" 1.67" 1.70" 1.75" 1.75"
July July July August August August August
9 15 23 3 15 23 so

E. 1.57" 1.62" 1.83" 1.96" 2.15" 2.32a 2.56"
H. 1.80" 1.84" 2.00” 2.32" 2.66" 2.95" 3.05"

According to a number of investigators (4),
(11).(12). (13). (20), (22). (28). (30). (32. (37):
and (39) the growth of peaches is definitely divi-
ded into three stages. This statement applies to
all varieties, but certain modifications must be
made for early clingstone varieties. First.---
Rapid development of the fruit, apparently due mainly
to increase in size of seed part, up to 68 days after
blossoming.

Second.-- Best period during which the seed is formed
and the stone becomes hard.

Third.-- Period of rapid growth of flesh to maturity,
beginning 4 to 5 weeks before ripening time.

”The second stage shows the greatest amount of

13

'variation. It may last for only one or two weeks
in case of the early varieties, or for four to seven
weeks in case of the later ripening varieties.

Farley (18) in 1923 studied, ”The Factors Influ-
encing the Effectiveness of Thinning”. Thinning
experiments were carried out on a comparatively large
number of trees by six methods :--

July 7-8 1. Early light 4. Early heavy

July 21-22 2. Medium light 5. Medium heavy
July 5 3. Late light 6. Late heavy

Light thinning consisted of removing the green.fruits
so that those left on the tree spaced 4 to 6 inches
along the branches, while the heavily thinned fruits
were spaced 6 to 8 inches. In light thinning 36.56 %
or 787 fruits were removed. The time of thinning did

not make any difference. Results were as follows:--

Thinning Date Value of Carmine & Belle

4 to 6 June 7 $ 172.00 3 351.00
4 to 6 June 21 171.00 461.00
4 to 6 July 5 138.40 335.00
6 to 8 June 7 191.60 269.00
6 to 8 June 21 176.70 339.25
6 to 8 July 5 138.70 345.00

Unthinned check plot 112.00 309.75

14

Summary
1. The statement commonly made that peaches should
be thinned before the pits hardened to secure satis-
factory results was not substantiated in this exper-
iment.
2. Early thinning was particularly effective with
comparatively early ripening varieties.
3. This experiment indicates a direct relation be-
tween the degree of thinning and the size of the
fruit.
4. The degree of thinning may be carried to such
extent that the advantage gained in size of fruit

will be lost by a decrease in yield.

Detjen (11) in 1926 made a study of the physiolog-
ical dropping of peach fruits. He found that the embryo
in the early stages is very small in proportion to the
rapidly developing ovule. None of the peaches that fell
during the week of the heavy drop had disintegrated ov-
aries. This should clear the idea regarding the import-
ance of pollination or fertillization and the relative
importance of embryo abortion of fruit shedding.

Dorsey and McMunn (12) in 1926 made a study of,
"The Development of Peach Seed in Relation to Thinning".
”First there is a period of rapid development of the

fruit apparently due mainly to increase in the size of

15

seed part. In Elberta this took place 35 days
following bloom during which time this variety
had reached the average diameter of 1.44 inches.
Since the stone begins to harden at about the end
of this time, this period is characterized by the
outlining of the stone in the flesh to nearly its
full size. .

"The second, or 'rest period', extending from
the 36th to the 68th day after bloom is featured
by a relatively slight increase in diameter and by
hardening of the stone.' The average increase in
diameter from 1.44 to 1.62 inches (measured through
the suture of the peach fruits), volume increase
during the second period would be about forty three
per cent. ‘

"The third, 'flesh forming period', extending
from about the 69 day to maturity. During this
time the volume of flesh increases very rapidly,
(in diameter from 1.62" to 2.36" or 209 per cent.)

"The stone reaches nearly its maximum size
by the 42 day. As in the stone there is a rapid
growth at first in the seed coats and in the nuc—
ellus, except for plumpness of kernel which begins

to harden. Before the kernel is one-fourth the

16

size it reaches at maturity the embryo sac has
extended full length of the nucellus. With fur-
ther growth in the seed there is an enlargment
and lengthening of the canal accompanied by fur-
ther elongation of the embryo sac. Therefore
the rapid growth in the stone and is an out-
standing feature of early growth of the seed.
"The embryo and cotyledons develop late in
the peach. Two months after bloom the embryo is
not often more than one-sixteenth inch in length
in the Elberta, and can.be seen as a small white
spot in the extreme tip of the nucellus. The
Table No. Iion the following page shows, "Sequence
of Development of the Fruit and Seed of Fflberta."
Dorsey and McMunn (15) in 1931 made an ex-
tensive study of seed size in relation to fruit
size in the peach, as related to peach thinning.
Table No. II on page 18 gives measurments show-
ing the increase in growth of the different parts
of the peach. An Elberta peach ls to 1% inches
diameter has 86.9% flesh. An Elberta peach 2
inches or more in diameter has 94.% flesh. Two
important facts are to be noted: (a) The flesh
increases in amount relative to the 'seed' as mat-

urity is approached. (b)'While the larger peaches

17

 

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18

tend to have larger ”seeds" the proportion of the

peach which is flesh increases with size.

Table II.

and ucMunn).

Measurements

showing the increase in
growth of different parts of peach.

(After Dorsey

 

 

 

 

 

 

 

 

 

 

 

~ (Dates
Measurements June June July July July July Aug.
23 28 '7 13 20 26 8
Avera e sut-
ured meter 1.51 1.55 1.57 1.62 1.82 1.95 2.24
in inches.
170 VOTER
of fruit 30.0 34.1 35.9 39.9 47.1 59.2 125.
. in ggams _~
verage wei-
ght 0f 868d 606 7.5 6e5 6e9 8e2 .705 1101
inggrams
"Per cent
flesh by 78.8 78.2 81.7 82.5 82.6 87.4 91.1
weight

 

 

 

 

It appears, therefore, from a number of angles

that the size of the "seed" or stones and the size

of the fruit are more or less closely related.

Summary and Conclusions

I. The stone does not increase

hardening process is under way.

II.

in size after the

The larger peaches tend to have larger "seeds".

The significance of this relationship commercially

is that conditions should prevail during the first

period which favor "seed” development or early growth

in the peach as a whole.

19

III. Early thinning did not, within a given tree ‘
condition, increase the size of the stones in the
fruit of a given size class as might be expected.

JFK The general growth conditions of the tree (is.)

whether high in carbohydrate or high in nitrogen,

influenced the stone size more than early thinning.

Section III. The Relation.2£_Fruit Size 33 Leaf

 

 

 

Area; Jones (26) in 1931-1932 reported that an
increase in the number of leaves per fruit was
attended by the following results:

I. When the leaf ratio was 10 to 1 vs. 45 to l
increasingly large fruit though not in proportion

to leaf area was produced.
II. Increase in sugar content.
III. Larger fruit mature earlier.
IW. Improvement in color of fruit.
‘W. Improvement in flavor of fruit.
Weinberger and Cullian (37) in 1932 studied
ratios of 10, 20, 30. 4O 60. and 80 leaves per
fruit on branches of 10 Elberta trees. The branches
were girdled June 13. The branches with the lower leaf

ratios, 10 and 20, produced by far the greatest number
of new leaves after girdling. With 1. leaves per fruit,

20

the peaches attained a size of 2.2 ounces (approx-
imately two inches in diameter), while with 20 leaves
per fruit, the final size was 3.6 ounces (2% inches).

A gééter number of leaves produced larger fruits

though not directly proportionately. Pit measurements
were made when the fruits matured and on.the whole

the heaviest pits were produced with the 80 leaf ratio,
averaging 6.92 grams, and the lightest with 10 leaf
ratio averaging 6.09 grams. The other pit weights

were directly correlated with leaf area. It was also
noted that fruit on girdled branches were over 20 per
cent larger than on normal branches. Thus the effect
of thinning of fruit on girdled branches is not strictly
comparable to thinning on normal branches. The accumu-
1ation of food caused by girdling the bark increases
the efficiency of the individual leaf in sizing the
fruit. The larger the leaf area per fruit, the more
noticeable is this effect. Allowance should be made
for this factor in interpreting results of this type

on a practical basis.

21

Objective

Since the leaves of the tree manufact-
ure the plant foods for the fruit and tree
growth, it seems reasonable that the number
of leaves per fruit (remaining on the tree
after thinning) should be a good basis for
the removal of excess fruit. The literature
cited shows that the different varieties of
peaches vary in.time of ripening and size.
The object of these experiments is to add
something to the present information concern-
ing the methods and time for the removal of
surplus peach fruits when the trees set, a
full crop. Mere specifically this investi-
gation aimed to determine the number of leaves
needed to produce fruit of a good size and.
quality without undue reduction in.quantity.

22

Description of Experiments Conducted

 

Orchard.- The studies were made on trees in the

, 'Mbuntain'View Orchard" located west of the city
limits of Romeo, Michigan,planted in 1927. The
land has a gradual slope toward the northwest.
The orchard was fertilized by broadcasting sul-
phate of ammonia which was harrowed into the soil.
Clean cultivation was practiced during the spring
and early summer, when the orchard was sown to
buckwheat as a cover crop, and the large sturdy
plants held the snow in the orchard during the

winter. Trees that had been injured or did not
seem to have normal vigorous growth were not used
in this investigation. The trees received uniform
spray treatments and uniform treatment for peach
borer. They were set 18 by 18 feet apart and were
given.moderate to light pruning each year.

Season.-- The seasons (1950-1951 and 1951-1952)

were favorable for both heavy set and good survival
of peach fruit buds. The thermometer rarely reached
the zero point during the winter. The summer of 1931
was rather hot and dry, withna light rainfall. The

summer of 1932 was warm with an average rainfall.

23

Methods of Investigation.-- The experiments were

 

begun during the summer of 1930 when records were
collected from branches about three fourths of an
inch in diameter. They gave the number of leaves,
and the number and weight of the fruits. These
records showed that branches of the same tree did
not produce peaches of the same size in proportion
to the ratio of leaves per fruit. These gfiEt differ-
ences made it apparent that practical tests should
be made on girdled branches. In June 1930 twenty
five branches were girdled on each of three var?
ieties;-- Dewey, Rochester. and South Haven. These-
girdles were about one fourth inch wide on branches
about one half inch in.diameter.. The girdles were
(wrapped with adhesive tape to prevent evaporation.
Two weeks after the girdles were made the variations
in growth of leaves and fruits were so great that
it was decided to count the leaves on whole trees.
This was done in July,193l. The data showed some
relation between leaf area and size of friuts and
the work was repeated in 1932.

The common.way of recording peach size is

transverse diameter in inches. In this work, howeven,

the fruits were weighed and the size recorded in

n:q.£.=.':‘ .9»...
'V ' ’ Q...‘\.J

24

ounces. Furthermore photographs were taken with the

fruits laid on.a graduated scale, as shown in Figure
I. For general comparison the weights and sizes of

ripe peaches are given as follows: Table III.

8 ounce peach 3 in. in.diameter 100 per bushel
6 ounce peach.2 3/4 in. in diameter 130 per bushel

4 ounce peach 2 1/4 in. in diameter 200 per bushel

3 ounce peach 2 1/8 in. in diameter 260 per bushel
2 ounce peach 2 in. in diameter 400 per bushel
1 ounce peach 1 1/2 in. in diameter 788 per bushel

 

 

C.

 

 

”-‘g

Figure I.Rochester Peaches from Thinned and
Unthinned Trees.

 

 

 

The peaches insthe figure at the right were
thinned to twenty five leaves per fruit. The photoe
graphed background scale lines are drawn so that the
lines are l”, 1%”, 2", 2%”,and 3" from the base.

One hundred fruits of each variety were selected
at random and weighed each week. Table IV, and

Figures 2, 3, 4, 5 and 6 indicate the progress of
growth made by each variety. These records of

25

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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08

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as

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Average Weight of Fruit in Ounces
IO

26

 

to 20 4 l8 1 15 29
June July August

Figure II. Graphs showing the rate of growth of
Dewey peaches from thinned and unthinned trees.

Average Weight of Fruit in Ounces

27

t

 

20 4 18 l 15 29
t
Da . June July August

Figure III. Graphs showing the rate of growth of
Rochester peaches from thinned and unthinned trees.

Average'Weight of Fruit in Ounces

28

 

O 4 18 ‘ 9 12
Date June July August September

Figure IV. Graphs showing the rate of growth of
South Haven peaches from thinned and unthinned trees.

Average Weight of Fruit in Ounces

29

 

Date 2 4 l8 1 15 29 12 26 30
June July August September

Figure V. Graphs showing the rate of growth of
Elberta peaches from thinned and unthinned trees.

Average Weight of Fruit in Ounces

50

 

Date

2 l 9 6
June July August September

Figure VI. Graphs showing the rate of growth of
J.H.Hale peaches from thinned and unthinned trees.

 

31

growth for each week and the graphs showing a com-
parisoncofttheggrowthcon thinned and unthinned
trees makes it quite apparent that peaches do not
vary a great deal in size until the rapid growing
or, "flesh forming"period" is reached shortly before
maturity. They also indicate that peaches increase :11
weight very slowly during the pit hardening and
seed formation period. According to Dorsey and
Mthnn (12) "the stone reaches nearly its maximum
size by the forty second day after bloom." It is
interesting to note the uniformity in growth during
both the rest period and the flesh forming periods

for the different varieties of peaches.

The Relation.of Leaf Number and Leaf Area
to Size of Peaches

Records were collected on branches one-half
inch to three fourths inch in diameter. The week
the fruits came to maturity the leaves were counted

and the terminal growth for the season measured in

inches. ‘When the fruits ripened the records were‘
completed for each branch by counting and weighing
the fruits in ounces. The records were collected

from each tree and are shown on the following pages.

52

 

 

 

 

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.b. 33.3..

Number of Leaves per Fruit

 

53

5 6

1 2 3 4
Weight of Fruit in Ounces

Figure‘VII. Graphs showing how size of Dewey peaches
increases with the number of leaves.

--—.As shown.by tree records.-»-—~Smoothed curve.

34

Dewey

The Dewey is one of Michigan's most highly
colored early market peaches and when the season
is favorable the trees develop a large number of
fruits. The trees do not have a heavy June drop
and hand thinning and moderately heavy pruning
are necessary to produce fruits of good size.
The fruits on the trees in the test plot were
thinned so that there would be approximately from
20 to 25 leaves per fruit. By actual count the
number varied from 16 to 27. The average prod-
uction for 10,000 leaves on thinned trees was
69.8 and for unthinned trees 76 pounds of fruit.
Highest production.was reached by tree Dmel5

on which 106 leaves on the average produced a
pound of fruit. The ratio of leaves per fruit
per fruit was 10 to one. The fruits averaged
(1.4 ounces) each and were too small for mar-
keting. The largest (2.77 ounce) fruits were
produced by tree D.A .2 on which there were 156
leaves to each pound of fruit. The average size
of thinned fruits was 2.31 and of unthinned fr-
uits 1.4 ounces, each. The increased value of
fruit produced by 10,000 leaves due to thinning
was $1.07.

35

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moo." moons use; newnenoom Bonn noaooom A; 33.3.

Number of Leaves per Fruit

56

 

1 2 3 4 5 6
Weight of Fruit in Ounces

Figure VIII. Graphs showing how size of Rochester peaches

increases with the number of leaves.
As shown.by tree records-— ------ Smoothed curve.

 

37

Rochester

Rochester peaches are somewhat larger and not
so highly colored as Dewey. This variety is class-
ed as one of Michigan's best early peaches when the
fruit on the tree is properly distributed to obtain
good sized fruits. When the season is favorable the
trees are heavily loaded and hand thinning and mod-
erately heavy winter pruning are advisable in Ob-
taining marketable fruits. The fruits on the trees
in the test plot were thinned so that there would
be approximately from 20 to 25 leaves per fruit.

By actual count the number varied from 24 to 29.
The average production for 10,000 leaves on thin-
ned trees was 87 and for unthinned trees 105 pc-
unds of fruit. The highest production.was reach-
ed by tree R.D.5 on.which 84 leaves, on the average
produced a pound of fruit. The fugitstavcraged
2.0 ounces each. The largest (3.8 ounce) fruits
were produced by tree R.A.7 on which there were
122 leaves to each pound of fruit. The ratio

of leaves per fruit was 20 to one. The average
size of the thinned fruits was 3.6 and of the un-
thinned fruits 1.9 ounces, each. The increased

value of fruit produced by 10,000 leaves due to

thinning was $1.13.

38

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Number of Leaves per Fruit

39

 

4 5
Weight of it in Ounces

Figure IX. Graphs showing how size of South Haven
peaches increases with the number of leaves.

*-—-As shown by tree records. — ----- Smoothed curve.

40

South Haven

The South Haven peach is one of Michigan‘s,
highly flavored canning and fresh market varieties.
When the season is favorable the trees are very pro-
ductive, and hand thinning should be resorted to.c“
The trees in the test plot were thinned so that there
would be approximately 20 to 25 leaves per fruit. By
actual count the number varied from 22 to 26 leaves
per fruit. The average production for 10,000 leaves
on thinned trees was 80.4 and for unthinned trees
103 pounds of fruit. Highest production was reach-
ed by tree SH.D.9 on.which 85 leaves on.the average
produced a pound of fruit. The ratio of leaves per
fruit was 9.5 to one. The fruits averaged 1.7 ounces
each, which would be too small for much market value.
The largest (3.2 ounce) fruits were produced by tree
S.H.A. l on which there were 114 leaves to each
pound of fruit. The ratio of leaves per fruit was 22
to one. The thinned trees averaged 23 and the un-
thinned trees averaged 11.1 leaves per fruit. The
average size of thinned fruits was 3.04 and the
unthinned fruits 1.8 ounces, each. The increased
value of fruit produced by 10,000 leaves due to
thinning was $. 84 .

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41

 

 

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«nod mocha nommm manonam Bonn monooom .HHH>.0Hme

Number of Leaves per Fruit

42

 

3 4 5 6
Weight of Fruit in Ounces

Figure X. Graphs showing how size of Elberta peach
increases with the number of leaves.

a——fi As shown by tree records.- ----- Smoothed curve.

43

Elberta

The Elberta peach is one of the most widely
cultivated varieties. When the season is favorable
the Elberta peach is one of Michigan's most prod-
uctive fruits. The trees in the test plot were
thinned so that there would be approximately 30
leaves per fruit. By actual count the number var-
ied from 25 to 37 leaves per fruit.' Average prod-
uction for 10,000 leaves on thinned trees Was 86,
and for unthinned trees 143 pounds of fruit. High-
est production was reached by tree F.248 on which
71 leaves, on the average produced a pound of fruit.
The ratio of leaves per fruit was 10.5 to one. The
ratio of leaves per fruit was 10.5 to one. The fruits
averaged 2.4 ounces each, which was a marketable size.
The largest (4.9 ounce) fruits were nroduced by tree
E.A.2 on.which there were 122 leaves to each pound
of fruit. The ratio of leaves per fruit was 37 to
one. The thinned trees averaged 31.2 and the un-
thinned trees averaged thirteen and two tenths lea-
ves per fruit. The average size of thinned fruit
was 43 and unthinned fruits 2.8 ounces, each. The
increased value of fruit produced by ten thousand

leaves due to thinning was $.44.

44

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Number of Leaves per Fruit

45

 

3 4 5 6 7 8
Weight of Fruit in Ounces

Figure XI. Graphs showing how size of J.R.Ha1e peach
' increases in size with the number of leaves.

—— As shown by tree records.--—--Smoothed curve.

46

J.H.Hale

The J.HlBa1e peach is one of Michigan's best
fancy market varieties, when the fall frosts do
not interfere with its maturity. When the season
is favorable, the trees are very productive and
hand thinning is advisable to produce large fancy
fruits. The fruits on the trees in the test plot
were thinned so that there would be approximately
from 40 to 50 leaves per fruit._ By actual‘eount
the number varied from 38 to 65. The average pro-
duction for 10,000 leaves on thinned trees was 85,
and the unthinned trees averaged 125 pounds. High-
est production was reached by tree H.D.7 on which
57 leaves, on the average, produced a pound of fr-
uit. The ratio of leaves per fruit was 15 to one.
The largest (7.! ounce) fruits were producgdl by

tree H.A.l on.which there were 135 leaves to each

pound of fruit. The ratio of leaves per fruit was
65 to one. The thinned trees averaged 50, and

the unthinned trees averaged 20 leaves per fruit.
The average size of the thinned fruits was 6.6,
and the unthinned fruits 3.9 ounces, each. The

increased value of fruit produced by 10,000 leaves
due to thinning was 8.90.

47

General Observations

Observations made during the 1930 and 1931

seasons seem to indicate that the rapidly growing
small fruits made a heavy draft on the trees food
supply. The fruits located where there was a suf-
ficient number of leaves to produce good growth,
matured to a good size, although they were clus-
tered on.the branch. ‘When the fruits were num-
erous and the foliage insufficient to produce good
growth many fruits and leaves dropped (See Figure
XV). Many of the leaves on trees bearing a hea-
vy load turned yellow and dropped approximately
the same time as the shrunken fruits. This cone
dition is more prevalent with the early varities.
Tests were made of the growth of fruits in res-
pect to development when the fruits touched each
other. Large clusters of fruit were left un-
thinned. The fruits were removed from adjacent
branches and the leaves were counted so that each
fruit had an average ratio of leaves per fruit of
25 to one. The branch was girdled below the food
supply. South Haven.branches (A) and (B) are
shown in the.Figure XII. The leaves surround-

ing the fruits were removed from (B). Branch

48

(A) originally had 26 peaches. The fruits developed
to good uniform size shown by figure XIII. This dem-
onstrates that peaches do not tend to shrivel and drop
if they have a sufficient supply of plant food, which

apparently they can Obtain from an adjacent branch.

 

 

 

 

 

 

(A) (B)
Figure XII Clusters of South Haven Peaches.

m

 

L

        
   
 

 

 

 

 

(A) (E)
Figure XIII Size of South Haven Fruits.

49

 

 

 

 

 

 

 

(A) (B) (C)

Figure XIV. Types of Peach Branches.
These three types of branches shown in FigureIIY
might be found on any variety of peach trees. The long

slender branch (A) with scattered leaves would not pro-
duce large peaches, although they were left eight inch-
es apart. The heavily foliated branch (0) with a large
number of new shoots has a large number of leaves and
on this branch the fruits might be left two inches ap-
art. Also, observations of the past three years indi-
cate that the long slender branch needs more leaves per

fruit than branches of type (B) and (C). It would be

50

good practice in thinning early varieties to leave
one peach for each 30 leaves on type (A), one for
each 25 leaves on type (B) and one for each 20 leaves

on type (E).

 

   

\ .1

317*

(1 leaves 0!";er
v

    
    
 

 

 

 

 

Figure XV. Shrunken Fruits and Leaf DrOpping

Figure XV of a South Haven branch shows pre-
mature defoliation and shrunken fruits. This was
a typical branch taken from a heavily loaded tree.
Many of the lower lateral branches loaded with fruit
lose all of their leaves before there is a natural

dropping of the surplus fruit. Also, many of the

leaves on the branches adjacent to the shrunken

51

fruits are discolored. It seems reasonable that
early thinning might prevent this premature defol-
iation and thus increase the productivity of the
tree. The photographs also indicate that Nature
does not remove enough surplus fruits to complete
the thinning process.

The records that have just been presented indi-

cate differences in pruning, in soil fertility or

water supply that caused a variation among the trees.
This difference in the number of leaves and produc-
tion had some influence on the size of the fruits,
but in spite of these differences, it is apparent
that thinning improved the size of fruits. For ex-
ample a thinned Dewey tree (D.A.ll) with 4135 leaves
thinned to 20 leaves per fruit produced fruits weigh-
ing 2.3 ounces each, and unthinned tree (D.D.5)

with 4225 leaves with 12 leaves per fruit produced
fruits averaging only 1.6 ounces each. A vigorous
Dewey tree (DtA.15) with 8050 leaves thinned tol$8.8
leaves per fruit produced 2.3 ounce fruits, and un-
thinned tree (D.D.3) with 7600 leaves with 10.6 lea-
ves per fruit produced 1.1 ounce fruits. This in-
dicates how fruits approximately the same size are
produced by a definite ratio of leaves per fruit.
Similar comparisons could be made with other var-

ieties.

52

It is interesting to compare the percentage

decrease in fruit production.by 10,000 leaves on
thinned trees, with the percentage increase in wood
which was measuredby shoot growth. Table X.indicates
that when peaches on the trees having a heavy set-
ting of fruit are thinned more wood growth is pro-
duced. It shows that when there is little or no
thinning the fruits get the first claim on the
food materials manufactured by the leaves, and sh-
oot and wood growth consequently suffer. On the
other hand, when the fruits are properly thinned,
relatively more food material is left for vegeta-
tive growth and consecuertly the growth of shoots
is longer and more vigorous. The 21.5 per cent
increase in shoot growth in the Elberta peach tree
wood was accompanied by a decrease of forty per
cent in fruit production. The 9.3 per cent in-
crease in wood or shoot growth on the South Haven
trees was accompanied by a decrease of 18 per cent
in fruit production. It is quite probable that
this decrease in production and comparative in-
crease in shoot growth according to a number of
earlier investigations (1), (19), (20), (20), (24),
(32), (30), and (37) conserves the strength of the
tree and seems to stimulate fruit bud set. Thinning

53

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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54

gave the smallest decrease of 8.1 per cent in.truit

production on Dewey trees, but thinning improved

the fruits which showed the greatest difference in

market value. This seems to indicate that thinning

is most beneficial to early peach varieties, but the

later varieties make greater increases in wood growth.
These results are from vigorous, well fertilized,

moderately pruned five year old trees. Trees that

are lacking in vitality have a heavier "June drop"
and if not thinned early, usually have a heavy leaf
drop during the pit formation period. Peach fruits
of an excellent quality can be produced by Michigan
growers when they instruct their thinners in properly
removing the surplus fruits from the heavily loaded
trees, providing such trees and soil conditions are
studied for each variety in its environment.

Table XI. Differences in'Varieties of Thinned Peaches.

 

 

 

 

Leaves per Size of Days Leaves Shoot growth ‘
'Variety fruit fruit growth per #‘ per 1,000
leaves
Dewey 20.6 2.3 91 142 352 inches
Rochester 26.0 3.6 98 318 . 396 ..
South Haven 23.0 3.04 108 124 316 ..
Elberta 31.2 4.3 126 116 406 ..
JQH.Hale 50.0 6.6 133 119 330 ..

 

 

 

 

 

Table XI, indicates the number of leaves needed

to produce an excellent quality of each variety of

peaches, and some of the variety differences.

55

The graphs (Figures VII to XI) on the growth
of each of these varieties shows that vigorous trees
with the indicated leaf ratios would produce approx-
imately the sized peach fruits indicated by'rable.XnI.

Table XIE.Approximate size of fruit (diamater inches)
as produced by the following ratio of leaves per fruit.

 

 

Leaf ratio Inches diameter of fruits produced
fruit Early Mid.season Late
15-20 to one '14} to 2" 1% to 2 1/8" 2 to 2 1/s"

 

20-25 to one 2 to 2 1/8" 2 to 2 l/8" 2 to 2%"

 

25-30 to one 2 1/8 to 23;" 2 1/8 to 2%,” 2 1/8 to 2%"
_

 

 

 

5040 to one 2 1/8 to 2%" 2 1/8 to 2%"
40-50 to one 2% to 3"
50-60 to one 2% to 3"

 

 

 

 

 

 

This investigation shows that the systematic remo-
val of surplus fruits can.be accomplished by first glan-
cing over the branch and estimating the number of leaves.
Then leaving the proper number of fruits to attain.the
desired size. If the tree has set a large number of
fruits on the inner slender branches (which are weaker
(6) ). the ratio of leaves per fruit should be doubled.
Those who favor pruning as'a thinning process (1), (3),
(6), (9), (13), (20), (22), (31). and (32) would remove

56

most of these slender inner branches by heavy
pruning. This process of pruning is favorable
to the production of large peaches on rapidly
growing shoots which usually have a light set of
fruit buds. The long shoots are not possibly so
hardy and do not withstand the cold winters as
well as the short hardier ones. However, when
these inner lateral branches are properly thinned,
300d sized fruits are produced. The operators
should be sure that each branch has a sufficient
number of leaves to develop good sized fruit. In
the terminal part of the branch (Figure XIV Type
(0) ),some of the lateral shoots or secondary
branches fail to set fruit. In this case the
operator should leave many peaches close together
on the main part of the branch. Furthermore when
only one half of the tree sets fruit the other
ha1f can‘be thinned accordingly because the food
materials from one side can.belp to produce larger
fruits on the other.

Peach thinners should accurately estimate the
number of leaves on.a branch. In doing this they
should make a study of the different types of branp

ches. Estimate the number of leaves per branch

57

then.count the number of leaves on.the branch.
By doing this a few times it is possible to
become efficient hand thinners of peach fruits.
Such employees are constantly reminded of the
fact that the leaves manufacturecthe tree's food
supply to grorfruits, new shoots, leaves, roots
and wood. When good sized fruits develop it is
an indication, that the food for good growth is
sufficient to supply all parts of the tree. Two
to three ounce peaches are easily sold on.the
early market but the later market demands a four
to six ounce peach.

The shoot growth on a tree is an indication
of thgtvdgor of its growth. Trees that are negle-g
gtedtpnoduce new shoots less than four inches long.
‘When the peach orchard is unfertilized, light pruning
is practiced and the soil poorly tilled the trees
have short shoot growth , and very severe thinning
should be practiced. Where moderate pruning and
good clean tillage are practiced the shoot growth
should be between.5 and 10 inches, and quite severe
thinning should be practiced. Under ideal orchard
conditions, where the soil is fertile or regular

applications of fertilizers are made, moderate

58

pruning is practiced and there is clean tillage
with a good cover crop sown every year, the new
shoot growth is from 6 to 16 inches, and moderate
thinning should produce good sized fruits. Where
the same soil conditions exist and heavy pruning

is practiced the shoot growth is from 8 toT84 inesx
ches and good sized fruits should be produced

when light thinning is practiced. Through-out

this work tree vigor has been considered because

it is an important factor influencing the size of
peaches. Ideal orchard conditions produce vigorous
trees that usually produce a good crop.

Peach growers hand thin.their fruits to produce
the largest possible amount of fruit that can attain
the highest commercial standard at the greatest
profit. The effort of the tree is to produce a
large number of seeds. The systematic removal of
surplus fruits requires good judgment and it is
difficult to give fixed rules that will fit every
growers condition. Nevertheless,some general rules
are desireable. From this_investigation.it would
seem that the following would apply fairly well to
Michigan conditions.

 

 

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_ . . 2 l. ..
- .fi .m_—x ‘L-l—A L- ‘

‘— ‘u—eh- i. ' _

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59

Rules for Thinning

1. Early varieties should be thinned first.

2. Thinning should be started as soon as it

it is evident which ones will fall off naturally
in the June drop, which occurs approximately 35
days after bloom.

3. The trees should be thinned so that the re-
maining fruits have the following ratio of leaves
per fruit; early varieties 25-35 to one; late var-
ieties 30-50 to one.

4. Thinning should be completed when the tip of
the pit begins to harden, but thinning is effective
within three weeks of fruit maturity, though it
will be less beneficial to the trees.

5. Thinning of fruit buds by annual moderate
pruning and a heading back renewal system, when

needed to keep the shoot growth vigorous is des-

irable in producing large peaches.

60

Summary of the Results of Investigation

1. Size of peaches is greatly influenced

by the ratio of leaves per fruit, which manu-
facture the plant foods for fruit growth.

2. The length of the growing period effects
the size of the fruit. For example a leaf
ratio of 25 to one, produce&,a 2.6 ounce Dewey
peach in ‘90 days and a 6.4 ounce Hale peach in

130 days.
3. Thinning reduced the total yield, but at

the same time, it increased the value of the
crop and produced improved commercial grades
of peaches.

4. Improved tree condition as influenced by
soil fertility, pruning and heading back in-
creases wood growth and size of the fruit.

5. Laborers who hand thin peaches should
be trained to estimate the number of leaves
on a branch and thin the fruits to a ratio

that will result in the desired size.

61

LITERATURE CITED

1. Barden, F.M. and H.J. Eustace.- Commercial

Peach Growing in Michigan.- Mich. Agr. Exp. Sta.
Specle Bill. 66. 1.50. 19130

2. Barden, F.M. and H.J. Eustace.-— Financial
History of a Twelve Year Old 0rchard.-— Mich. Agr.
Expo Sta. Bul. 940 19180

3. Biglow, W.D. and H.C. gore.- Studies on

Peaches.-— U.S. Dept. Agr. bu. Chem. Bul. 97.
1-320 1919'

4.
4. Blake, M.A.-—Growth of Fruits of Peach.-

N. Jer. Agr. Exp. Sta. Ann. Rept. 40 : 82-88. 1919.

5. Blake, M.A.-— The Growth of the Fruit in the

Elberta Peach from Blossom to Mhturity.*- Pro. Am.
Soc. for Hort. Sci. 22: 29-39. 1925.

6. Blake, M.A. - New Jersey Standard for Clas-
sifying the Set of Fruit Buds upon Peaches. -—
N. Jer. Agr. Exp. Sta. Ciro. Bul. 271. 1933.

7. Blake, M. A. and C.H. Connors. - The June
Drop of Peaches.-— N. Jer. Agr. Exp. Sta. Ann.
Repte 27: 70-77. 19140

8. Chandler, W.H. - Fruit Growing.- p 77.1925

9. Chandler, W.H. - North American 0rohards.-—
p 305e 19280

10. Close, C.P. - Peach Thinning Experiments.-
Ann. Rept. Del. Agr. Exp. Sta. 94-98. 1902.

ll. Det en, L.R.- Physiological Dropping of Fruits.
_ D61. 81'. Exp. Sta. B111. 430 1-4 0 926.

12. Dorsey, M.J. and B.L. McMunn.&¥ The Develop*
ment of Peach Seed in Relation to Thinning.-— Proc.
Am. Soc. for Hort. Sci. 23: 402-414. 1926.

.C‘.

13. Dorsey, M.J. and R.L. McMunn.- Relation of
the Time of Thinning of Peaches to the Growth of
the Fruit Tree.-— Proc. Am. Soc. for Hort. Sci.
24: 221. 1927.

14. Dorsey,M.J. and R.L. McMunn.— Peach Thinning
Experiments.- Transactions of the 111. Sta. Hort.

Soc. 1928.

15. Dorsey, M.J. and R.L. McMunn.- Seed Size in
Relation to Fruit Size in the Peach: The Fourth
Report on the Illinois Thinning Investigations.—
Proc. Am. Soc. for Hort. Sci. 29: 13-22. 1932.

16. Dorsey, 15.3. and R.L. McMunn.- Fruit-Seed
Dimensions in Elberta Peach.-— Proc. Am. Soc. for
Hort. Sci. 30: 145. 1933.

17. Dorsey, M.J‘. and R.L. McMunn.- A Seven-Years
Study of Fruit Bud Level in Elberta Peach.-- Proc.
AM. 800. for Hort. 801. 50: 176. 1933e

18. Farley, A.J.-- Factors Influencing the Effect-
iveness of Thinning.- Proc. Am. Soc. for Hort. Sci.
20: 145a 192030

19. Fraser, S.-- American Fruits.- p 437. 1924.

20. Gardner,V.R., Bradford and Hooker.-— Funda-
mentals of Fruit Production.-— p 290. 1922.

21. Gardner, Bradford and Hooker.-- Fruit Product
tion... p 183. 19270

22. Gardner, Marshall and Hootman.- Size of Peaches

and Size of Crop.-- Spcl. Bul. Agr. Exp. Sta. Mich-
State 0011689. 184: 20.25. 19280

23. Gould, H.P.-— Growing Peaches,Sites and Cultural
Methods.-— U.S. Dept. Agr. Farmers Bul. 1917. 1923.

24. Hall, W.—- Burbank in Your 0rchard.- Saturday
Evening Post.-— 198: 28 and 184. 1926.

25. Johnson Earl S.-- Moisture Relations of Peach
Buds During the Winter and Spring.-- Md. Ebcp. Sta.

Bul. 255 . 1923.

63

26. Jones, I.D.-— Relation of Soil Moisture and
Leaf Area to Fruit Development of Georgia Belle
Peach.*fl Proc. Am. Soc. for Hort. Sci. 28. 1931.

27. Jordan, A.T.-— Pruning and Thinning.- N.
Jer. Agr. Exp. Sta. Ann. Rept. 11: 196-97. 1898.

28. Keffer, G.A.-— Insuring the Peach Crop.-—
Am. Fruit Gr. Mag. 46: 3 and 29. 1926.

29. Knowlton, H.E. and M.B. Hoffman.—- Size of
Peaches as Affected by the Time of Thinning.-—

Proc. Am. Soc. for Hort. Sci. 25. 277-29. 1928.

30. Lilleland, Osmond.- Growthoof Study of the
Peach Fruits.-— Proc. Am. Soc. Hort. Sci. 29.1932.

31. Lloyd, J.W.-— Thinning the Peach Crop.-— Am.
Fruit Gr. mag. 46: 3 and 29. 1926.

32. mcHatton, T.H., H.W. Harvery and G.H. Firio.-
Peach Growing in Georgia.-— Ga. Sta. Col. Bul. 169:
1-52 e 1924 e

33. McMunn, R.L.- Relationship Between Volume and
the Dimensions of the Elberta Peach.-— Proc. Am.
Soc. for Hort. Sci. 30: 187. 1933.

34. Powell, E.L.-— The Orchard and Fruit Garden.-
p 99. 1905.

35. Penny, E.L.-— Changes in the Composition of

Growi Peachel.—~ Del. A r. . Sta. Ann. Re t.
14: aggas. 1902. 8 Exp p

36. Walker, E.-— Peach Growingg in Arkansas.-Ark.
Agr. Exp. Sta. Bul. 79: 43-68. 1903.

37. 'Weinberger, JQH. and F.P. Cullinan.-— Further
Studies on the Relation Between Leaf Area and Size
of Fruit Chemical Composition, and Fruit bud Form-
ation.-—Proc. Am. Soc. for Hort. Sci. 29: 23-31.1932.

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