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RESUMENARY RESULTS OF
BLUEBERRY 5325 AND WELD EN
RELATION TO THE TIME OF PECKENG

Thesis for the Degree of M. 3°
MICHIGAN STATE SOLLEGE
Roger Siam Yaunq
$617

M-795

Date___

This is to certifg that the

thesis entitled

presented by

has been accepted towards fulfillment

of the requirements for

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PRELIMINARY RESULTS OF BLUEBERRY SILK AND

YIELD IN RELATION TO THE TIME OF PICKING

BY
Roger Stacy Young

A Thesis
Submitted to the School of Graduate Studies of Michigan
State College of Agriculture and Applied Science
in partial fulfillment of the requirements

for the degree of

MASTER OF SCIENCE

Department of Horticulture

1947

 

THESIS

I

Table of Contents
Page
Introduction.............................. 1
Methods and Materials..................... 1
Results................................... 4
Conclusions and Summary................... 1?
Acknowledgments........................... 18

Literature CitedOO...OOOOOOOOOOOOOOOOOOOOO 19

Introduction

The blueberry of the highbush type, flaggininm
.ggzzmbgsnm, comprising most of the commercial plantings
in.Michigan is a bush which may reach twelve feet in
height under favorable conditions. The inflorescence, a
raceme, develops either terminally or from lateral buds
in the axils of leaves on new shoots with all buds of the
cluster in full bloom within three or four days of each
other. The first fruit to ripen is that at the tip of-
the raceme. The later berries are harvested at the base.
The first berries to ripen are larger than those which
ripen later.

Commercial growers usually harvest the berries at
approximately one- to two-week intervals, depending on
the variety and the grower. The first picking is made
as soon as the fruit has become blue or blue-black in
color.

This paper reports the results of tests at South
Haven Experiment Station, South Haven, Michigan, to
determine the best time of picking blueberry fruits for
maximum size and yield, and includes determinations of
sugar and acid content and the growth and development
of the fruit.

Methods and Materials
The two most important commercial varieties grown

in Michigan, Rubel and Jersey, were selected for the

2 .
study. The plants were grown on Saugatuck sandy loam soil.

The six-year-old Jersey plants were on a soil having a
slightly higher content of organic matter than the soil on
which the seventeen-year-old Rubel plants were growing.

The plants were carefully selected for uniformity on
the basis of stem diameter. Johnston (4) has shown that
growth and productivity are related. The work of Brightwell
and Johnston (2) indicates that the diameter of the laterals
has an influence on the size and yield of the fruit.
Accordingly 30 plants, calipered six inches above the soil
level, were arranged in three plots in which the total stem

diameters were nearly equal. The diameters are listed in

 

 

 

table 1.
Table 1. Total stem diameter of the plots.
Variety Plot No. Stem Diameter (Inches)
Jersey 1 90.8
2 91.6
5 90.8
Rubel 1 150.7
2 150.9
3 150.7

 

 

 

 

 

The plot pickings were determined as the season
progressed. The first plot was picked at the time of the
first commercial picking and a second and a third plot were
picked at later dates. The time interval between the
picking of plots 1 and 2 for both varieties was seven days.
Plot 3 of the Jersey variety was picked 21 days after the
picking of plot 1 and the interval between the picking of

5
plot 1 and plot 5 of the Rubel variety was 18 days. The

pickings were continued at two-week intervals for all plots
until all berries were removed from each plant in order
that the second, third and fourth pickings of the plots
would have the same time interval as the initial pickings.
Only the blue or blue-black colored berries were picked as
would be the case in the picking of the berries in
commercial fields. -

Thirty individual berries of Rubel, taken at random,
were tagged and measured every second day beginning July 15
and ending at the time the berry fell from the plant. The
transverse and axial diameters of each berry were measured.
The volume calculated from the measurements of transverse
diameter was found to closely approximate the actual
displacement volume. This comparison is shown in table 2.

Table 2. Volume Comparison.

 

 

 

 

Stage of ripeness Volume in ml. calculated V31/6IID3
Transverse Axial Displacement
diameter (in) diameter (in) rye/m I (m2

Full ripe 1.456 0.695 1.57
1.98 0.904 1.7
1.458 0.695 1.5

Half ripe 0.696 0.582 0.6
0.796 0.452 0.78
0.591 0.582 0.6

Green 0.58 0.21 0.55
0.464 0.25 0.45
0.268 0.145 0.22

 

 

 

 

 

Size and yield records were kept on the individual

plants throughout the season.

The weighings and the cup

counts were made immediately upon picking the fruit.

4
The size determinations were made by counting the number

of berries required to fill a measuring cup. Chandler (5)
has shown that blueberry size is accurately measured by
the cup count method.

A noticeable difference was observed in the taste of
berries depending on the time of picking. On August 5, a
series of berries for the determination of total acid were
picked in the following stages of growth (a) green,'

(b) oneéquarter ripe, (c) one-half ripe, (d) three-quarters
ripe and (e) full ripe.

One Rubel and four Jersey plants were allowed to
remain unpicked to determine how long the berries would
adhere to the plant. One Rubel and three Jersey plants
were first picked 50 days after the initial picking of
plot 1. One Jersey plant was not picked until 49 days
after the initial picking of plot 1.

Results

The data on the yields of the Rubel and Jersey
varieties are tabulated according to the plant and the
picking date in tables 5 and 4. Table 7 is devoted to the
yields of those plants which were not included in the three
plot experiments but on which the initial picking was
delayed until late in the season.

The berry sizes as determined by the cup count method
are tabulated according to the plant and the picking date
in tables 5 and 6.for the three plots. The fruit counts of

5
those plants which were not picked until 50 days and 49

days after the initial picking of plot 1 are recorded in
table 8.

Since blueberries do not mature uniformly, the
measurements of a given day are not an indication of
maturity; therefore the change from green to blue or blue-
black fruit color was considered an accurate indication of
the time that berries had reached the same state of
maturity. Volumes were computed for the berry measurements
taken for the specified intervals before or after the
appearance of the blue or blue-black fruit color regardless
of the date on which the color appeared. The transverse
volumes were averaged and are shown in figure 1.

The data for the sugar and acid content determinations
for the four stages of fruit development, determined by
Special adaptations of the standard proceedures, are shown
in figure 2 *. The total sugar is expressed in percent of
fresh weight and the acid content is expressed in milli-
liters of N/lO acid per gram of fruit.

At the time of each picking, berries were packaged and
placed under simulated shipping conditions by having one

pint of berries carried in an automobile for four or five’

* The chemical analyses for sugar and acid content
were done by Dr. E. J. Benne, chemist, Michigan Agricultural

Experiment Station, East Lansing, Michigan.

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 5. Yield of Rubel Fruit with the Dates at T0p of
Column for Each Plot, South Haven, Mich., 1946.
Plot Plant Picking Picking Picking Picking Total
N0. N0. 1 2 5 4
(92.) (02.) (02.) (02.) (02.)
1 7-22 8-5 8—19 9-2
1 26 90 49.5 5.5 169
2 25 86.5 56 6.5 152
5 54.5 58.5 21 8 142
4 28.5 84.5 48 10.5 171.5
5 24.5 81 51 8 144.5
6 25 108.5 28 4 165.5
7 44.5 90 19.5 6.5 160.5
8 24 46 15 5 88
9 42 58 15.5 5 118.5
10 27.5 58.5 65 1.25 152.25
Av. 51.75 74.15 52.85 5.42 144.17 (90)*
2 7-29 8212 8-26
11 57.5 61.5 15 154
12 77.5 57 14.5 149
15 71.5 55 9.5 116
14 61 90 26 177
15 68 61.5 17 146.5
16 71.5 42 18 151.5
17 54.5 46 11.5 112
18 51.5 27 5 81.5
19 68 27 4 99
20 62.5 59 9 110.5
Av. 64.55 48.6 12.75 125.7 (79)
5 8-9 8-25
21 156 19 155
22 77 6.5 85.5
25 89.5 15 102.5
24 108.5 15 125.5
25 92.5 8.5 101
26 118 26 144
27 88.5 9.5 98
28 105 12.5 115.5
29 100 22.5 122.5
50 106 16 122
Av. 101.9 14.85 116.5 (75)
Sum Total 1978.5 1575.5 445 54 5895.7
(125) (86) (28) (5) (242)

 

* Reduced to the nearest pound.

 

7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 4. Yield of Jersey with Dates at Top of Column for
Each Plot, South.Haven, Mich., 1946.
Plot Plant Picking Picking Picking Picking Total
No. No. 1 2 5 4
(02.) (02.) (02.) (02;) (02.)
1 7-25 8-6 8-20 9-5
1 17.5 115.5 61.5 21 215.5
2 15 95.5 75.5 25.5 205.5
5 25 125.5 58.5 15 222
4 11 89.5 75.5 25.5 201.5
5 12 145.5 99.5 27 284
6 19.5 95.5 66 26 205
7 20 115 75 18 224
8 17 112.5 85 25.5 258
9 15.5 104.5 90 54 242
10 12 127.5 65.5 15 220
Av. 16.05 111.85 74.8 22.85 225.55 (141)
2 7—50 8-15 8-27 9-10
11 80 106.5 27 5.5 217
12 65 95 56.5 4 196.5
15 40.5 47 40.5 2 150-
14 45 65.5 46 1 157.5
15 76.5 108 44.5 4 255
16 58.5 85 54 7 184.5
17 48.5 115 87.5 22 275
18 51.5 118 75.5 18 261
19 65.5 162 67.5 8 501
20 94 100 20.5 1.5 216
Av. 60.0 100.0 49.75 7.1 216.95 (156)
5 1-14 8-26 9-9
21 108 57 7‘ 152
22 150.5 59.5 4 194
25 210 64.5 9 285.5
24 166.5 62 15 245.5
25 157.5 46.5 4 208
26 245.5 78 9 552.5
27 162 72 15.5 249.5
28 168.5 67.5 8 244
29 187.5 79 17 285.5
50 159 54.5 6 199.5
Av. 169.5 60.0 9.45 259.0 (149)
Sum Total 2455 2718.5 155.9 299.5 6814
(155) (170) (84) (19) (426)

 

* Reduced to the nearest pound.

 

8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 5. Cup Counts of Rubel Berries
P10t Plant Picking Picking Picking Picking Average
N0. No. l 2 3 4
1 7-22 8—5 8-19 9-2
1 1
2 18? 5% 3:153 213 3133.2
3 215 304 315 249 290.5
224 259 295 208 201.5
5 222 353 233 273 270.5
0 198 290 287 372 288.3
7 198 254 308 335 273
8 200 307 308 369 297.5
9 220 241 319 300 271.5
10 249 303 282 ... 278
Av; 212.2 284.1 284.2 303 270
2 41—29 8—12 8—20 9-9
11 233 301 274 209.3
12 177 253 275 235
1 225 292 283 200.0
1 210 257 290 250.3
15 197 253 05 251.6
10 220 293 90 303
17 192 229 239 220
18 21 200 232 232
19 25 337 300 2 .5
20 217 208 284 250.3
Av. 214.9 274.8 287.8 259
3 8-9 8-23 9-0
21 235 273 254
35 588 335 575.5
24 211 290 250.5
25 215 242 228.5
20 218 245 231.5
2; :48 27 302.5
2 O
29 2% 3%., 22% 5
30 231 278 254.5
Av. 23b. 5 272’b 254.5
Grand Average 221.2 277.0 280.0 303.0 201.5

 

 

 

9

Table 0. Cup Counts of Jersey Berries

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P1 t P1 P1 k' Pi ki Pi ki Pi ki A
N3, Ngrjt Cling 02 ng . 03 ng 04 ng verage
1 7-23 8-0 8—20 9-3
1 115 206 278 256 213.7
2 116 1 26 2 18
53 130 194 29 22% 22
4 11 1 1‘ 1 1 .
5 12 13% 12:8 523 12% 5
6 136 194 200 236 191.
7 125 167 168 227 171.
8 114 126 132 164 13
9 129 144 1 9 169 1 7.7
10 127 179 194 268 192
Av. 123.8 166 205.3 228.2 180.8
2 7-30 8—13 8-27 9—10
11 12 150 161 246 171.5
12 16 201 188 252 200.5
1 195 29 230 ... 239.3
1 220 27 231 ... 2 1.6
15 130 154 161 194 159.7
16 169 16 188 279 199.7
17 148 1 183 E56 182. 7
18 125 159 165 51 175
19 13 133 138 207 152.7
20 13 1 8 184 155.3
Av. 154.4 181.9 182.9 240. 7 185.9
3 8-14 8—20 #949
21 154 179 259 197.3
22 184 19g 252 211
23 167 20 252 209
182 190 225 189
:2 1 6 196 248 203. 3
132 171 244 182.3
161 225 287 224.3
28 144 195 285 208
29 134 196 272 200.6
30 165 191 257 204.3
Av. 155.9 194.8 258.1 202.9
Grand Average 144.7 180.9 215.4 233.3 189.9

 

 

 

 

 

 

10
Table 7. lields of a Single Plant of Rubel Picked August
23, 1940; Three Plants of Jersey Picked August 23, 1940

and One Plant of Jersey Picked September 9, 1940.

 

 

 

 

 

 

 

Variety Picking 1 Pickin 2 T0tal

5(02.) (OZ. (02.)

Rubel 8-23

198.5 198.5 (12.4)*
Jersey 8-23 9-9

10 .5 .5 111

143.5 4 140.5

138.5 8.5 147

Av. 128.2 6.6 134.1 (8.4)

Jersey 9—9

73-0 73-0 (4.5)

 

 

 

 

 

* Reduced to neareSt pound

Table 8. Cup Counts of the Rubel and Jersey Plants Picked

AuguSt 23, 1940 and September 9, 1940.

 

 

 

 

 

 

Variety Picking 1 Picking 2 Average
Rubel 8-23
227 227
J 88 8-2 -0
er y 1763 360 218
145 ' 208 170.5
139 179 159
Av. 153 215.0 184.5
rse —
Je y I73 174

 

 

 

 

 

 

 

 

 

 

13 »
days, an average of 550 miles, and one pint being held in a

building which was 5° to 5° F cooler than the outside temp-
erature. At the end of the allotted time, the fruit was
examined for wilted and moldy berries, firmness and general
appearance. The data were not consistent, that is, the
moldy and wilted berries and the firmness of the berry
varied regardless of the time of harvest. In general the
Jersey variety appeared to be firmer the later the initial
picking was made and withstood the simulated shipping and
handling conditions much better than did Rubel;

The results of these experiments were influenced
greatly by weather conditions. The rainfall during the
month of July was 0.05 inches. The extreme dryness con-
tinued throughout the month of August when the rainfall was
oneéhalf the average. Berries were noticeably smaller in
size and lower in weight and in some cases they shrivelled
and fell from the plants.

The total yield of plot 1 of Rubel was 90.1 pounds of
fruit (table 5). The total yields of p10ts.2 and 5 were
78.7 pounds and 75.2 pounds respectively. On each progres-
s ively later date of picking the yield of fruit was less.
For the complete harvest,plot 5 required two pickings and
plot 2 required three pickings as compared to four pickings
for plot 1. The wide variations in yields of the individual
plants could not be correlated with the total stem diameter
nor the number of stems per plant.

The yield per picking varied greatly in Rubel. The

14
total yield for the first picking of all three plots was

125.6 pounds as compared with 86.8 pounds for the second
picking, 27.8 pounds for the third picking and 5.4 pounds
for the fourth picking. Here again the yield per picking
decreased as the season progressed, or as the numharof
pickings required to remove all the berries from the plant
increased. It might be expected that as the season
progressed the yield would reach a maximum before decreas-
ing. Perhaps this would have been true in the case of
Rubel had the first picking been made earlier in the season.

The yield records of Jersey (table 4) were different
than those of Rubel. The total yield for plot 1 was lower
than for plot 5, 140.9 pounds to 149.5 pounds. Plot 2 had
the lowest yield, possibly because three plants were
severely infected with a leaf spot disease. The infected
plants, numbered 15, 14 and 16, yielded 8.2, 9.8, and
11.5 pounds as compared to the plant average of the plot,
15.5 pounds.

In Jersey the yield at the second picking was larger
than the first followed by a decreasing yield in the third
and fourth pickings. The first picking yielded 155.4
pounds as compared with 169.9 pounds for the second, 85.7
pounds for the third and 18.7 pounds for the fourth picking.

In order to determine how long a plant could go with-
out a picking and still produce a good yield, one Rubel and
three Jersey plants were left unpicked until 50 days after
the initial picking of plot 1 and one Jersey plant was left

15
unpicked for 49 days after the initial picking of plot 1.

The one Rubel plant yielded 12.4 pounds of fruit which was
1.5 pounds more than any single plant used in the three
plots. The total stem diameter of this one plant was 16.85
inches as compared with 15.14 inches, the average for the
plants of the three plots. Four plants of the three plots
had larger total stem diameters than this one Rubel plant
picked 50 days after the initial picking of plot 1, yet
they did not produce so heavily.

. The three plants of Jersey picked 50 days after the
first picking of plot 1 yielded 8.5 pounds of fruit per
plant as compared with the average of 14.2 pounds per plant
of the thirty plants of the three plots. The one Jersey
plant picked September 9, 49 days after the first picking
of plot 1, yielded 4.5 pounds. The great reduction in the
yield of this one plant can be accounted for by destruction
or loss of fruit by birds. The berries which were picked
were in good condition and held up well in the package.
These observations suggest that the plants should not be
picked as early as is the practice among growers.

There is a gradual increase in size of fruit from one
month before ripe (blue or blue-black) fruit color appear-
ance until approximately eight days before the-ripe fruit
color appears, at which time the rate of increase is
accelerated (figure 1). This accelerated rate continues
for twelve days after the ripe fruit color appears and then

rapidly decreased. The data indicate that the berries

16
should not be picked as early as the color changes from the

green to the blue-black color.

The cup counts indicate that the average berry size
decreased as the number of berries left on the plant becomes
fewer. The later maturing berries are fully developed but

do not become as large as those that mature earlier. Cup

counts for the Bubel variety (table 5) show an increase in
the average size of berry as the initial picking of the
plot is delayed. These results may be due to the fact that
the plants of plot 5 were picked half the number of times
of those of plot 1.

The size of the Jersey berries decreases as the number
of pickings is increased and as the initial picking of the
plot is delayed (table 6). The average berry size of the
three plants with the initial picking delayed for 50 days
was larger than the average berry size of the second plot.
The one Jersey plant which was not picked until 49 days
after the earliest picking of plot 1 produced the largest
berries.

The relationship of the total sugars, expressed in
percent sugar, and the total acid content, expressed in
milliliters of N/10 acid per gram, as the berry develops
' from the green to the full ripe stage is Shown in figure 2.
The acid content decreases as the sugar concentration
increases. These results are similar to those of Alwood
(1) for grapes. Just how much the percent sugar increase

:and the acid decrease when the berry is left on the plant

17
to a later date was not determined.

Conclusions and Summary
The relationship between the time of harvest of
blueberries and the yield and size of fruit is reported
for the varieties Rubel and Jersey growing under Michigan
conditions. This report is based on one season's work in
which unusually dry weather played an important part in
influencing the size and weight of berry. In spite of
these limitations, the following conclusions may be drawn.

1. From 50 days until eight days before the
change in fruit color, green to blue-black,
the fruit growth is slow compared with the
growth between the eighth day before and
thetwelfth day after the fruit color change.

2. The first picking of the plant yields the
largest sized berries with a gradual decrease
in all later pickings.

5. An increase in the average size of the berry
occurs as the initial picking of the plot is
delayed and as the number of pickings
required to harvest all berries are reduced.

4. Total yield of Jersey increases While that
of Rubel decreases as the initial picking is
delayed and the pickings required for the
removal of the berries from the plant are

reduced in number.

18
Acknowledgments

The author wishes to express his sincere appreciation
to Dr. H. B. Tukey, Michigan State College Horticultural
Department, and to Professor S. Johnston, Michigan
Agricultural Experiment Station, South Haven, Michigan,
for their assistance and criticisms in the planning of the
studies; to Dr. E. J. Benne, chemist, Michigan Agricultural
Experiment Station, for his work in determining the sugar
and acid content of the fruit; and to Drs. N. L. Partridgeznui
J. Moulton, Michigan State College Horticultural Department,

for their suggestions in the preparation of the manuscript.

19

Literature Cited
Alwood, W. B. Development of sugar and acid in grapes
during ripening. United States Dept. of Agric. Bul.
555, 1916.
Brightwell, W. T. and S. Johnston. Pruning the
highbush blueberry. Mich. Agric. Exp. Sta. Tech.
Bul. 192, 1944.
Chandler, F. B. The relationship of different methods
of expressing size of blueberry fruits. Amer. $00.
for Hort. Sci. 59: 279-280, 1941.
Johnston, S. The influence of various soils on the
growth and productivity of the highbush blueberry.
Mich. Agric. EXp. Sta. Quar. Bul. 24: 507-510, 1942.

 

 

 

 

 

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