This is to certify that the

thesis entitled

COMPARISON OF MODELS FOR PREDICTING END OF REST
OF FLOWER BUDS AND USE OF EVAPORATIVE COOLING
TO DELAY BLOOM IN SWEET CHERRY (PRUNUS AVIUM L.)

 

presented by

MICHAEL BARR MILLER

has been accepted towards fulfillment
of the requirements for

M.S. degree in Horticulture

Mfloémg .

Major professor

 

 

Date ”'18'77

 

0-7 639

 

:0

 

 

 

MARISONIOFIVDIEISFUR PREDICI'INGENDOFREST
OFFIOVTERBUIBANDUSECFEVAPORATIVECIDLING

‘IODEIAYBUD’IINSWEE'I‘CHERRY (PRUNUSAVIUMLJ

 

By

Michael Barr Miller

A THESIS
Sukmitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER (1“ SCIENCE
Department of Horticulture

1977

ABSTRACT

Cmparison of bbdels for Predicting end of Rest
of Flower Buds and use of Evaporative Cooling
to Delay Blocm in Sweet Cherry (Prunus avium L.)

 

By

Michael Barr Miller

Evaluations of two mathematical chill unit nodels (i.e.,
Utah Pheno-Climatography and Rabertson-Stang Ohio nodels) relating
environmental temperatures to rest canpletion of sweet cherries

(Prunus avian L.) were conducted under Michigan conditions.

 

Accumulation of chill units began Septanber l, for the years 1975
and 1976, and continued until no later than February 13. Estimation
of rest carpletion of sweet cherry was found to be more accurate
using Robertson and Stang's chill unit nodel.

Following the canpletion of rest cultivars "Hedelfingen"
and "Emperor Francis" were sprinkled intermittently using an over-
head sprinkling system to delay blocm by evaporative cooling.
Sprinkling was begun March 8, 1977 and ended April 19, 1977. Water
application began when ambient tenperatures rose above 7 . 2°C
utilizing a 2 minute on - 1 minute off cycle. Sprinkling was

continued until controls reached full bloom. Treated trees reached

Michael Barr Miller

full bloan 2 days after the controls, with slightly nore delay

inthetopsofthetreatedtrees.

WW3

I wish to express my sincere appreciation to Dr. F. G. Dennis,
Jr., advisor and friend, for his guidance, insight, and aid in my
research and writing. Special thanks are given to Drs. E. H.

Kidder, D. H. Dewey, and J. A. Flore, rrenbers of my Guidance
Committee, for their assistance and counsel.

I also wish to thank the following persons for their encourage-
ment or assistance with the thesis problem Doer Cleveland, Doug
Archbold, and Daniel Diaz .

Averyspecialthanks is extendedtomyparents, Mr. aners.

Barr Miller for their help and understanding.

ii

TABLECF CCNI‘ENI'S

Page
LISTOFTABIES..1V
LISTOFFIGURES.......................V
INTROIIJCI‘IOV........................1
CHAPTER I: EVAIIJATION 01“ 'Im CHILL UNIT NDIEIB IN MIOIIGAN . 19

ABSTRACI‘....................18
MEMSANDIVE'HIOIB..............20
RESLLTS..23
DISCUSSIQIAMDCCNCLUSICNS ........... 25
LITFRMURECITEDZG
CHAPTER II: DELAYING Em OF swam CHERRIES BY EWXPORATIVE
ABSI‘RACI‘..28
WANDIWGJSWWM
DISCUSSION.....................39
LI'I'ERA'IURECITED41
SUM‘lARY...........................42

Bm‘ImPIIY O O O O O O O O I O O O O O O O O O O O O O O O O 4 2

LIST OF TABLES

Table Page

11W REVIEW

1. Formulae for determining chill units utilizing daily
mmdmmnandmfinimntemperatures.............. 7

2. Conversion of selected tarperatures to chill units. . . . 9

3. Chill units required to complete rest for various fruit
afisI I I I I I I I I I I I I I I I I I I I I I I I I I 10

4. Simmaryofcmrentsprirflclingdata. . . . . . . . . . . 13-14

5. Sveet cherry bloom dates (cv. Schmidt) and dates of last
springfreezeinVanBurenOounty,M[.......... 15

6. Summary of three years research on 6 to 15 day bloom
delay of pears by evaporative cooling. . . . . . . . . . 16
CHAPTER I
l. bibnthly and total chilling hours accumulated at Blooming-
dale, m in 1975-76 and 1976-77 as determined using two
mels I I I I I I I I I I I I I I I I I I I I I I I I I 24
CHAPTER II
1. Effect of overtree sprinkling on lnxl weight (mg/bud) for
sweet cherry cultivars 'Emperor Francis' and 'Hedelfingen'
1977 I I I I I I I I I I I I I I I I I I I I I I I I I I 35

2. Effect of evaporative cooling on frost injury and fruit
at in mt m, 1977I I I I I I I I I I I I I I I I 36

3. Effects of evaporative cooling on size and maturity of
wt My 1977 I I I I I I I I I I I I I I I I I I I 38

iv

Figure Page

CHAP'ERI

1. Method of calculating chill units from maximum and
minimum temperatm'es, using method of Robertson and
Stang (1977). Data for Bloomingdale, ME.
Septarber29,l977.................... 21

INTKDDUCI'ICN

.Although low winter temperatures sometimes cause severe injury
to sweet cherry flowers in Michigan, azmcnecauumx1<xxnnnxmmmeis
late spring injury during bud swell or bloom. The goal of most
efforts to prevent losses during freezes has been keeping bud tempera-
tures above damaging levels. Heaters, wind machines, and overhead
sprinkling for freeze protection are among the more camon methods
available. However, these methods provide protection only under
specific weather conditions. If wind and cloud cover are not
favorable, much of the available heat is dissipated. .A large water
source must be available in order to effectively sprinkle for frost
protection. Once sprinkling has begun, usually at slightly above
00C, it must be continued until temperatures rise above freezing.
Cbst of operation using these methods has risen in recent years due
to the rising cost of fossil fuels, water availability, and stricter
anti-pollution legislation.

fibre recently attempts have been made to delay bud develop-
ment, thereby increasing cold hardiness during spring frosts. Chemical
sprays, such as ethephon, which delay opening, offer a potential
method for reducing spring freeze injury in tree crops,tmn:none has
proven camercially acceptable (Dennis, 1976) . The use of cryopro-

tectants, which increase the resistance of tissues to injury, is

another possible means of reducing losses.

In 1973, a group of researchers at Utah State University
(Alfaro et al. , 1974) developed a method for increasing spring-
time cold hardiness of flower buds by use of evaporative cooling
following rest carpletion. Evaporation of water from the buds
cools them enough to reduce the rate of growth and therefore delay
bloam. Current thought (Anderson, 1977) is to use sprinklers early
in the season, after rest completion, when temperatures rise above
7.2°c. Predicting the end of rest, when buds begin to swell in
response to warm weatler, is critical for efficient use of the
system.

The amount of cooling and delay in bud break possible by
this method is related to tie maximum amount of evaporation possible.
Since evaporation occurs faster in a warm dry atmosphere, Utah, with
_ lower relative humidities than Michigan, would be a better location
for evaporative cooling. Significant delays have been recorded in
Utah (Alfaro et a1., 1974) but response to this technique under
Michigan's less than optimum conditions, was unknam wl'en this
study was begun.

My objectives were to 1) test tie accuracy 'of two chill unit
models (Richardson, 1974, and Rabertson et a1., 1976) in predicting
rest completion , and 2) determine tlre efficacy of evaporative

cooling for bloom delay of sweet clerries (Prunus avium L.) in

 

Michigan .

LITERATUIEREVIEW

LITERATUREREVIEW

Part A. Determining end of rest.

 

Daring the course of evolution, most perennials have adapted
their growth cycles to survive seasonal environmental extretes of
temperature, sunlight, and water availability. Tie necessity to
withstand low temperatures during the winter season forced higher
plants, including fruit trees, to form buds either in late summer
or early fall, at a time when temperature and light conditions are
favorable for continued growth.

Coville (1920) deronstrated that certain woody plants
(e.g. blueberries), in cold climates did not require low temperature
in order to resume growth, but that chilling hastened flowering and
increased tle number of flowers. Nbst deciduous fruit trees mmst under-
go a period of chilling before "normal" growth resumes.

Chandler (1937) defined rest as the period when the plant
will not grow even though temperature and moisture conditions are
favorable. The rest period, hmever, should not be confused with
dormancy. Dormancy indicates inactivity due to any cause (Weinberger ,
1950) . Thus a tree in its rest period is dormant, but in northern
latitudes rest may have been completed, yet the tree remains dormant
because of low temperatures .

Fruit trees must experience a certain number of hours of

chilling temperatures in order for rest to be broken. Hutchins
(1932) suggested the use of the mmmber of hours at or below 7.2%
as a quantitative measure of chilling. Chandler (1937) noted that
temperatures just above freezing are more effective in breaking
rest than temperatures at or below freezing; re also established

a chilling requirerent for apple . Dbre recently, Erez and Lavee
(1971) reported the optimum chilling terperature to be 6°. £11ng
or lower temperatures were less effective. A temperature of 21°,
when alternated daily with low terperature, nullified the low
temperature effect; a high of 180 had no effect. Interrupting

tl'e chilling with tvo separate periods of 11 and 12 days at 200 had
no nullifying effect, but greatly enhanced lateral leaf bud break.
Tlese facts led to tleir (Erez and Lavee, 1971) prOpOsal of weighted
chilling hours, with tie relative value of chilling varying with
tetperature.

Various attempts have been made to evaluate the amount of
chilling required in the orchard. (he of the first such studies
was conducted by Weldon (1934) who correlated the occurrence of pro-
longed rest in a peach orchard with the average maximum daily tempera-
tures during December and January. The chilling requiretent was
satisfied when tie monthly average temperature was below 9.20C.

Weinberger (1950) , following up on Hutchin's work, proposed
tl'e use of accumulated hours below 7.2°c as an index of chilling.
Bennett (1950) pointed out that not all terperatures below 7.20 are
equally effective, and that terperatures below the freezing point

are ineffective. Most atterpts to determine chilling requirexents
for species and varieties, however, have been carried out with tie
traditional computation of the number of hours below 7.20. The
authors often do not specify wrether hours below tie freezing point
have been included or not.

Weinberger (1950) exposed peach twigs to tetperatures of
7.2°c or lower for 700, 900, or 1100 hours, then brought them into
awarmroem. If 50%oftleflowerbudsbecamegreenin3weeks,
rest was considered to be broken . Various other methods for eval-
uating chilling requiretents have been tried. Crossa-lhynaud (1955)
computed chill units using daily maximum and minimum terperatures
in relation to a threshold temperature of 7°C (Table l) . Bidabe (1965)
likewise utilized daily maximum and minimum temperatures, but
associated tlese values with appropriate 010 coefficients to attempt
to account for the varying effects of different temperatures on
growth and development (Table l) .

In 1974, Richardson et a1. developed a weighted chill unit
system from previous observations made by Erez and lavee. (he hour
of exposure at 60 represents one chill unit. Values become less than
one as temperatures drop below or rise above the optimum value. A
negative contribution occurs at terperatures above 150 and no
contribution to chilling occurs at temperatures below 0° (Table 2) .
The number of chilling hours required to satisfy rest requiretents

is genetically determined and varies with both species and cultivar.

Table 1. Formulae for determining chill units utilizing daily

maximum and minimum temperatures.

 

 

Metrod lz Crossa-Raynaud:

 

Hf = 31:11: x 24
H f = Daily cold units
7 = Threshold temperature (0C)
M = Maximum daily terperature

m = Minimum daily temperature

Method 2y B. Bidabe:

_ -M -m
At ‘ Q1016 + Qlo T6

Af = Accumulated daily cold units

Q10 = Coefficient representing a specific respiration-temperature ratio

 

M = Maximum daily terperature
m = Minimum daily temperature
2

From Crossa-Raynaud 1955 .

yFrom B. Bidabe 1965.

Some values calculated using the "Utah model"are given in Table 3.

Ibbertson and Stang (1977) proposed a new model based upon
conditions in Ohio. It differs from the "Utah model" by first allow-
ing for differences in effective chilling tetperatures among species
(e.g. , apple vs. peach) and secondly in tie chill unit coefficients
assigned to varying temperature ranges (Table 2) .

To determine the chill unit accumulation for a 24 hour period,
a computer program may be used to convert each hourly temperature
to the equivalent chill-unit value given in Table 2 . Since hourly
temperatures needed to calculate chill units are usually not avail-
able in orchards, a metlod was developed by Richardson et a1. (1974)
which syntresizes hourly temperatures using daily maximum and
minimum temperatures. Tests for 2 years covering the winter season
at Salt Lake City Airport gave chill-unit accumulations within 2% of
tie accumulation obtained using measured hourly temperatures .
(Richardson et a1., 1974) .

In Georgia, predictions made by utilizing the daily maximum
and minimum temperatures ("Utah model") were within 8.7 (i 5.7) days
of the values obtained using hourly temperatures (Cnesness et a1. ,
1976) . Discrepancies might have been due to the milder winters
experienced in Georgia.

Both models have been proven accurate within the envirorments
for which they were designed. During 1974 in Utah, rest carpletion

was observed in peach leaf bud samples on February 3. The calculated

Table 2. Conversion of selected temperatures to chill units.

 

Chill unit contributed per

 

Method 12
hour at indicated terperature
Iggp. (0c)
< 1.4 0
1.5 - 2.4 0.5
2.5 - 9.1 1
9.2 - 12.4 0.5
12.5 - 15.9 0
16 - 18 -O 5
> 18 -l
Me__treq_ .2? = sees £92211
< 1.4 0 0
1 5 - 2.4 1 0 5
2 5 - 9.1 l 1
9.2 - 12.4 1 0.5
12.5 - 15.9 0 0
16 - 18 -0.5 -1
18.1 — 21.0 -1 -l
> 21 0 0

 

zFrom Richardson et a1. 1974

yFran Robertson and Stang 1977.

10

Table 3. Chill units required to complete rest for various fruit

 

 

 

treesz.
Species Cultivar Chill units
Apple 'Delicicus' 1234
Apricot - 720
Cherry 'Bing' 880
Peach 'Elberta' 800
Pear 'Bartlett' 1210
Prune 'Italian' 818

 

ZFram Richardson et a1., 1975.

11

date using the model was February 1, 1974.

Part B. Delaying bloom to avoid freeze injury.

 

Overhead sprinkler irrigation has proven effective for
evaporative cooling of many fruits and vegetables grown under adverse
temperature conditions. In various studies since 1963 (Miller, 1963;
Van den Brink and Carolus, 1965; Chessness and Brand, 1969; Wheaton
and Kidder, 1966) reductions of 2.8 to 3.9OC in ambient temperatures
of various fruits and vegetables were noted. Wheaton and Kidder
(1966) reported an increase in yield of snap beans which they attributed
to overhead sprinkling. Gilbert (1970) and Unrath (1972) both reported
an increase in fruit quality and improved fruit size in their work
with grapes and apples , respectively.

Until 1973 , most experimental work with overread irrigation
dealt with evaporative cooling of crops which were in full foliage ,
or frost control as a result of teat of fusion of ice during bloom
stage (Gilbert, 1970; Gray, 1970).

Alfaro et a1. (1974) departed from tie classical approach
to frost control. Rather than protecting open blooms, trey delayed
bloom by evaporative cooling of the flower buds after the corpletion
of rest. Apple and cherry flowering was delayed 17 and 15 days
respectively. This was achieved through intermittent sprinkling
of the trees at a rate of 1.8 mum/hr wrenever the ambient tempera-
ture was above 7.20C.

Since this original work, similar methods have been tried

12

throughout tle United States and Canada with various species of
fruit (Table 4).

Current tl'iought is to use sprinklers for evaporative
cooling early in tie season, then change sprinkler heads for frost
protection as bloom approacl'es (Anderson, 1977; Lipe, 1977) .
Anderson (1977) stressed that bloom delay need not be prolonged,

10 days being enough in most years to avoid injury. If a 10 day
delay in bloom of sweet clerries were possible in southwest
Michigan, evaporative cooling muld have been beneficial in reduc-
ing frost damage in 6 of tie past 10 years (Table 5) . Bloom delays
of more than 10 days may reduce fruit size at harvest, as reported
by Icmbard (1977) for pears.

Problem may occur during or following sprinkling. Excessive
bud drop has been noted in peach (Buchanan, 1977; Lipe, 1977) .

Disease can also be a problem. Pseudoronas syringae has been severe

 

in at least ore orchard in California and Stang (1976) reported
problems with fireblight and "wet feet" with his work with 'Golden
Delicious' apple in Ohio. Lombard (1977) reduced frost damage to
pear with evaporative cooling in 1977 , but fireblight infection was
increased , particularly in the Bose cultivar . Other physiological
problems which Lombard attributed to evaporative cooling cancelled
any berefits gained from frost avoidance (Table 6).

13

 

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15

Table 5. Sweet crerry bloom dates (cv. Schmidt) and dates of

last spring freeze in Van Buren County, MI.

 

fl r

 

 

Predicted
Last freeze effect on frost
Full Petal at 05 below damage with 10
bloom fall -1 . 1 C day bloom delay
1967 4/30 5/9 5/3 prevent
1968 4/20 4/30 5/7 no effect
1969 4/28 5/5 4/30 prevent
1970 5/4 5/10 5/6 prevent
1971 5/7 5/16 5/13 prevent
1972 5/15 5/23 5/10 no effect
1973 4/26 5/8 5/17 no effect
1974 4/30 5/5 5/10 sore effect
1975 4/23
1976 4/16 4/21 5/19 no effect
1977 4/19 4/24 4/29 sore effect

 

16

Table 6. Summary of three years' research on 6 to 15 day bloom

delay of pears by evaporative cooling2 .

 

 

 

 

Respgnse Per cent of cases in which the

response was significantly
Increased Decreased

Fruit set 25 19

Yield 6 41

Fruit size at harvest 24 76

Seed content of fruit 71 0

Maturity based on pressure testy 0 18

 

zFrom Icmbard, 1977.

yIncreased - maturity hastened; Decreased - maturity delayed.

CHAPTERI

EVALIRTICN OF M CHILL UNIT ROMS

IN MICHIGAN

l7

Evaluation of Two Chill Unit Models in Michigan

Abstract. 'IWo mathematical models (Utah Pheio Clima-
tography and Robertson-Stang Ohio models) relating
environmental temperatures to rest completion of sweet

cherries (Prunus avium L.) were evaluated under

 

Michigan conditions. Accumulation of chill units
beganSepterberlanderriednolatertlanFebnary 13
for the years 1975 and 1976. Tre model developed by
Robertson and Stang proved to be more accurate in

predicting the end of rest in Michigan.

18

19

Dormant buds of deciduous fruit trees will grow slowly,
if at all, during late fall and early winter, even if temperature
and soil conditions are favorable. This physiological condition,
termed "rest" is broken by sufficient exposure to chilling
temperatures.

Several metteds have been developed for determining rest
completion. The standard method of taking cuttings from the
orchard and reting growth of 50% of the buds after 2 to 3 weeks is
time-consrming (Calculation of the number of tours below a critical
temperature, generally 7 . 2°C, leads to great variability between years ,
for the chilling effect varies with temperature, with little or re
effect below 0° (Bennett, 1950) .

In 1974, Richardson et al. proposed a weighted chill unit
model which assigned varying chill imit coefficients to different
temperatures. Coefficients ranged from -1 to +1 depending upon
the effectivensss of the terperature in satisfying rest.

Ibbertson and Stang (1977) made a few alterations in the
"Utah model" to allow for differences in emiroment and differences
among species in response to chilling terperatures.

I computed rest requirerent for sweet cherry using both of
these latter models to determine which model best applies under

Michigan conditions .

Materials and Metleds

Daily maximum - minimum terperatures during fall and winter
of 1975-1977 were obtained from the Natioral Weather Service station
at Bloomingdale, MI , the location of the test plot.

Assuming chill unit accumulation began on September 1 for
each year , a daily terperature curve was approximated by plotting
maximum and minimum terperatures for each day . Maximum terperatures
were assumed to occur at reon, whereas minirmmm temperatures were
plotted at midnight . These points were connected with a straight
line, which was divided into 12 equal segments with the end point
of each segment represelting an leurly terperature . Each ieurly
temperature was then assigned the proper coefficient from either
the Utah or the Ohio chill unit model (Fig. 1).

On February 13, 1977, cuttings were taken from the test plot

in Bloomingdale, MI, to see if rest were corpleted. The test plot
consisted of 20 sweet cherry trees approximately 12 years of age.
The trees were planted on a 7.3 x 8.5 meter grid, and were approxi-
mately 4.6 meters high. Four cultivars, Hedelfingen, Emperor Francis,
Viva, and Sam, were located within the plot, but only 'Hedelfingen' and
'Emperor Francis' were tested for completion of rest.

Two cuttings were taken from two trees of each cultivar

and placed in a mist bed at a te'tperature of 20 : 3°C. The mmmber

20

Fig. . l.

[netted of calculating chill units from maximum and minimum

temperatures, using method of Ibbertson and Stang (1977) . Data
for Bloomingdale, MI, September 29, 1977.

mmrmmm (0C)

Hours x coefficient = chill unit

I”, “h 3 x -1 = -3

 

 

 

)m ‘W 3x45=-L5

 

!“h. 2.25 x o = o

 

v (“WW (I

12PM

11.5 x +1 = 11.5

sum=7

 

 

12AM I2PM

TIME

21

SJNHIDIJJHCD IIIIm TIIFD ON

22

of buds which had reached Stage 3 (Ballard et a1. 1971) was

recorded on February 21, 1977.

Results

Using the Utah model, only 538.5 hours were accumulated
during 1975-76 and only 479.5 hours during the 1976-77 chilling
period (Table 1). On the other hand, the Ohio model indicated a
chill unit accumulation of 879.5 hours during 1975-76 and 800.75
hours during 1976-77, both of which closely approximate the
chill unit requirement (880 hr) reported for sweet cherry by
Richardson et a1 (1975).

At least 50% of the buds on sweet cherry twigs sampled
February 13 had reached Stage 3 on February 21 and, therefore,
rest was broken following the accumulation of 800.75 chilling

hours or less.

23

Table l . mnthly and total chilling hours accumulated at
Bloomingdale, MI in 1975-76 and 1976-77 as deter-

mined using two models.

 

 

Month Utah Model Ohio Model (Apple)
1975 ‘- 76
September 75.8 199.5
October 168.5 313.0
November 196.2 243.0
Decerber 98.0 124.0
January 0 0
February2 0 0
Total 538.5 879.5
1976 - 77
September 117.0 37.2
October 291.0 392.0
November 218.0 268.5
December 51.0 61
January 0 0
February 36.5 42
Total 479.5 800.7

 

 

 

ZNo chilling temperatures occurred until February 10,1976,wren

rest was presumed to have been completed.

Y Rest corpleted on or before February 13, 1977 as determined by

forcing cuttings.

Discussion and Conclusions

From evaluations of both chill unit models using approxi-
mated hourly ambient terperatures, Robertson and Stang's (1976)
model for apple was feimd to be the more precise at predicting end
of rest of sweet cherries under Michigan conditions.

The reasons for this appear to be due to differences in
environment from which the models were developed. The Utah model
was designed to function under a sunny-arid environment, whereas
the Ohio model more closely simulated the cloudybhumid growing
conditions of Michigan.

I conclude that the Ohio model is the more logical choice
for determining the eld of rest of sweet cherries in Michigan.
Through its use, a more precise and rapid netted of determining
end of rest is possible. With more precise records of end of rest,
the time at which to start sprinkling for bloom delay through

evaporative cooling may be determined .1701? e accurately.

25

Literature Cited

Ballard, J. K., E. L. Proebsting, Jr., and R. B. Tukey. 1971.
Critical tetperatures for blossom buds. Cherries.
Wash. State Univ. Ext. Cir. 371.

Bennett, J. P. 1950. Temperature and bud rest period. Effect
of terperature and exposure on the rest period of deciduous
plant leaf buds investigated. Calif. Agr. 4: 11-16.

Richardson, E. A., S. D. Seeley, and D. R. Walker. 1974. A
model for estimating the cotpletion of rest for ' Redhaven'
and 'Elberta' peach trees. HortScience 9: 331-332.

, , , J. L. Anderson, and G. L.
Ashcroft . 1975 . Phere-cllmatography of spring peach
bud development. HortScience 10: 236-237.

 

Robertson, J. L., and E. J. Stang. 1977. Personal commmication.

26

CHAPTERII

DELAYINGBILXMOFSWEEI‘CHERRIES

BY EVAPORATIVE (IDLING

27

Delaying Bloom of Sweet Cherries by Evaporative Cooling .

Abstract. Sweet cherries (Prunus avium L. , cultivars

 

"Hedelfingen" and "Emperor Francis") were sprinkled
intermittently using an overhead system. Sprinkling
began March 8 , 1977 , approximately one month after

the completion of rest. Water was applied using a 2
minute on - 1 minute off cycle, whenever the day temp-
erature was greater than 7 . 2°C (45°F) until the control
trees reached full bloom (April 19) . Treated trees
reached full bloom 2 days after the controls, with

slightly more delay in the tops of the trees.

28

The loss of fruit from spring frost ras been a perennial
problem. After rest has been completed, the rate of bud develop—
ment depelds upon the tetperature of the surrounding environment .
If the early spring teiperatures are below rermal, blossoming
is delayed; tewever , when terperatures are considerably above
normal, bud developrent accelerates , increasing the potential for
serious damage from a late spring freeze.

Sprinkler irrigation has been successfully erployed to
modify the micro-environment of many crops. Recently Alfaro et a1.
(1974) have used overhead sprinkling in Utah to evaporatively
cool fruit buds and thereby delay bud development 10 to 15 days.
Considerable delay has been reted in other locations throughout the
United States and Canada.

The maximum effect might be expected in an arid environ-
ment, such as Utah, where relative humidity is low and evaporation
is rapid . The higher relative humidity under Michigan conditions
slows the rate of evaporation and hence reduces the cooling effect.
Sunlight increases bud terperature above air terperature. Under
the more overcast conditions in Michigan, bud terperature might be
expected to remain lower than air temperature and evaporation rates
would be slower; therefore, one would expect less cooling and less

bloom delay. Delays of up to 9 days have been reported for apple

29

30

in Ohio (Stang, 1976) and 5 to 7 days for the same species in
New York (Swartz et a1) .

My purpose was to determine if evaporative cooling would
delay bloom of sweet cherries under Michigan conditions , and what

effects it might have on yield and fruit quality.

Materials and Metleds

The experimental plot consisted of twenty sweet cherry
trees approximately 12 years of age located near Bloomingdale,
Van Buren County, Michigan. The trees were planted on a 7.3 x
8 . 5 meter grid and had attained the height of approximately
4.6 meters. Four cultivars, Hedelfingen, Emperor Francis, Viva,
and Sam, were included within the sprinkled plot, but only
Hedelfingen and Emperor Francis trees were used for measuring the
effects of the treatment.

A sprinkler was placed in each of twenty trees. A 4.6 m
galvanized iron riser, 12.7 mm in diameter, was fitted with a
"Rainbird Full Circle Sprinkler - Nbdel 14-V-TNT", with a 1.6 mm
nozzle. Specifications for proper operation required at least
2.1 kg onz. Actual rezzle pressures varied from 2.6 to 2.7 kg cm2
with a projected application rate of 0.044 liters/sec per sprinkler
head. The diameter of coverage was 11.6 m, allowing for more than
sufficient overlap.

Water was obtained from a deep well approximately 99 . l m
from the first row of sprinkled trees. A PVC main (25.4 mm diam.)
supplied water to each of four laterals of the same diameter.

Each of the laterals in turn delivered water to five sprinkler heads.

A 24 four day-night timer turned the current on at

31

32

8:00 a.m. and off at 8:00 p.m. Water flow was controlled with

a thermostat which activated a variable 30 minute timer at tempera-
tures above 7.2%. The timer in turn controlled the 'on-off'

cycle of the well pump. A lapse time accumulator recorded total
operating tours. A second soleeid was controlled thermostatically
to open at tetperatures at or below 0°C to drain the line and
thereby prevent ice from rupturing the system.

Maximumeinimum thermometers and rain gauges were installed
in both sprinkled and rem-sprinkled plots. Sprinkling began March
8, 1977. A 3 min on - 3 min off cycle was tried initially, but due
to rapid evaporation the cycle was changed to 2 min on - l min
off on March 15. Sprinkling ended April 19, 1977 after 35 days
of operation.

Weekly precipitation and daily maximum and minimum terpera-
tures were recorded in both the sprinkled and ten-sprinkled plots.
Differences in bud temperatures were measured on April 14 using a
hand held potentioreter and copper constantan thermocouples (3 mil) .
Weather conditions were cloudy with a slight breeze, and ambient
teiperature was 14.4OC.

At approximately weekly intervals from (March 8 to April 8)
one and two year old branches were collected from two trees of each
cultivar in both the treated and control plots. Ten flower buds

from each of 2 branches on each sampled tree were weighted (10 buds/
weighing).

33

Bud samples were also taken on April 8, 1977 to evaluate
frost injury during tie previous night (minimum terperature of
-5. 5°C) . Three to four l-year-old steots were selected from two
trees of each cultivar in both the sprinkled and rem-sprinkled
plots. Buds were cut tranversely and the total numbers of injured
and non-injured flowers recorded. Approximately 100 flower buds
were counted May 6 on two limbs of each cultivar within each plot,
and the numbers of dead and living flowers and developing fruits
were subsequently recorded.

Fruit samples were harvested from both plots on June 16.
Eight samples (2 samples per tree, 25 fruits per sample) of
'Hedelfingen' and six samples of 'Emperor Francis' were taken within
each plot. Color, weight, suture diameter, firmness, and soluble
solids were recorded. Diameters were measured with calipers.
Fruits were separated into 4 color categories from 1 (light red) to
4 (deep red) and numbers of fruits in each category were recorded.
Each sample was then weigled and 10 fruits from each sample were
arbitrarily selected for determination of firmness and soluble
solids. A duroieter was used to measure flesh firmness following
reroval of a portion of tie epidermis, then the soluble solids
content of each fruit was determined with a hand refractoreter.
Data were analyzed by analysis of variance, and Duncan's (55)

multiple range test was used for mean separation.

Results

Sprinkler operation. Total sprinkling time during 35 days of

 

Operation was 127 hours, with a total of 236 mm of water being
applied at an average rate of 1.9 mm/hr. The total rainfall
during tl'e same period was 88.6 mm, for a total of 324.6 mm in

the sprinkled plot.

Terperature variation. Maximum air teiperatures were consistently

 

lower within the sprinkled block with differences of from 0.6 to
4.4OC between the two plots; however, minima were similar for both
blocks. On April 14, sprinkled buds were 2.2 to 3.9° cooler than

non-sprinkled buds.

Bud development. Bud weights were ret affected by sprinkling until

 

tl'e fourth week of sampling. Differences were apparent on April 2
(Table 1); however, variability was high and the differences were
non-significant at tie 5% level. Average values for sprinkled buds
were consistently lower on all sampling dates with one exception

('Hedelfingen', March 8).

Frost injury. Sprinkling reduced frost injury to buds of both

 

cultivars in samples collected April 8 (Table 2) , altleugh
differences were rem-significant at the 5% level. A difference

of only 6% was reted in 'Enperor Francis' while tl'e difference in

34

 

 

 

 

 

Table 1. Effect of overtree sprinkling on bud weight (mg/bud)
for sweet cherry cultivars 'Enperor Francis' and
'Hedelfingen' , 1977.

Sampling date
Treatment Replicate 3/8 3/17 3/27 4/2 4/8
'Emperor Francis'
Control 1 41 45 52 83 78‘
2 44 38 50 76 83
3 38 55 70 - 81
4 e 4_7 _6_4 :_ 9.9
Mean 39 46 59 80 82
Sprinkled 1 42 40 47 58 72
2 32 47 67 61 82
3 40 41 56 - 61
4 19 :42. :35 -_ 7_0
Mean 38 41 56 60 71
'Hedelfingen'
Control 1 39 45 57 69 81
2 38 42 54 55 84
3 35 46 55 76 -
4 93 3E 2.1. 23 :_
Mean 36 43 54 68 83
Sprinkled l 39 35 50 66 52
2 37 37 50 54 54
‘ 3 49 33 48 - 56
4 .32 $1. 19 :_ 353
Mean 40 37 48 0 55

 

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‘Hedelfingen' was 12%. Flowers of 'Hedelfingen' appeared to be

more frost hardy than tlese of 'Fmperor Francis' .

Bloom delay. The control trees reached full bloom (an estimated

 

50% of blooms open) on April 19, tie sprinkled trees approximately
2 days later, with variation within a single sprinkled tree of up
to 2 days. Flowers at the top of the sprinkled trees, which were
closer to the sprinklers, showed slightly more delay tlan those
on lower limbs. Less variability was noted on trees within the
interior of the sprinkled plot. Both cultivars were equally

retarded in development .

Fruit set. Data for fruit set (Table 2) were analyzed only for the
cultivar 'Hedelfingen' due to limited replication. Sprinkling signi-
ficantly reduced tle mmber of fruits developing per 100 buds as well
as tie number of fruits per 100 living flowers. Data for 'Emperor

Francis' paralleled tl'ese for 'Hedelfingen' .

Fruit maturity. Diameters and weights of fruits from non-sprinkled

 

'Emperor Francis' trees were smaller than those from sprinkled trees
(Table 3), while tl'e reverse was observed in 'Hedelfingen' . None of
these differelces was significant. Neitl'er soluble solids rer fruit
firmness was affected by sprinkling in either cultivar. Oorparisons
of sprinkled and ten-Sprinkled fruits revealed re obvious delay in

color development .

38

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Discussion

The effects of evaporative cooling on bud temperature are
influereed by solar radiation, ambient temperature , relative humidity
and wind velocity. Under Michigan conditions , solar radiation is
reduced due to cloudy skies ,_ and relative humidity is higler in
comparison with conditions in Utah. Therefore, one sleuld ret expect
as much bloom delay in Michigan as in Utah. However , with adequate
wetting of tie buds, and initiation of sprinkling as soon as possible
in the spring, a delay of one week sleuld be possible. In this work,
buds were ret thoroughly wetted ; apparently a finer spray of water
will be necessary for this to occur. Cycle oranges could be made
to increase the time spent sprinkling , but witreut adequate coverage
of the flower buds, the additional water would be wasted. Unevenness
of bloom on the lower limbs of sprinkled trees indicated inadequate
wetting. Branches near the sprinklers in the tops of trees, on the
other hand, were fairly uniform in delay. In order to attain an even
delay of bloom, a mist or cotbination mist and sprinkler system is
needed which would ret be overly affected by wind.

Frost injury to buds was decreased slightly as a result of
retarded development. Further tests of tardiness at different stages

of bud developrent are needed due to conflicting reports on the

effects of evaporative cooling. Bauer et a1. (1976) found buds of

39—

4O

peach which had been retarded by sprinkling to be less hardy 'than
tle controls, while Swartz et a1. (1977) noted greater hardiness of
sprinkled apple buds.

Fruit set of 'Hedelfingen' was significantly decreased.
This could be the result of reduced pollen production or viability
due to water present on the flower buds, or of desiccation of

tissues whel sprinkling was discontinued.

Literature Cited

Alfaro, J. F., R. E. Griffin, J. Keller, G. R.Hanson, R. L.
Anderson, G. L. Ashcroft, E. A. Richardson. 1974.
Preventative freeze protection by preseason sprinkling
to delay bud development. ASAE Paper No. 73-231,
Amer. Soc. Agr. Engr., St. Joseph, MI.

Bauer, M., C. E. Claplin, G. W. Schneider, B. J. Barfield, and
G. M. White. 1976. Effects of evaporative cooling
during dormancy on 'Redhaven' peach wood and fruit bud
hardiness. J. Amer. Soc. Hort. Sci. 101: 451-454.

Dtmcan, D. B. 1955. Multiple range and multiple F tests.
Bioretrics 11: 1-42.

Stang, E. J. 1976. Personal communication.
Swartz, H. J., L. J. Edgerton, and L. E. Powell, Jr. 1977.
The potential of evaporative cooling to delay bud break

and dehardening of deciduous fruit trees in New York.
The New York State Hort. Soc. Proc. 122: 172-174.

41

'SUIVMARY

With modifications allowing for better coverage , I feel
there is a potential for delaying bloom.and thereby increasing
cold.hardiness of sweet cherry with evaporative cooling. An
accurate model (e.g. Ohio.Model) for predicting rest completion
is essential in order to achieve maximum delay. The earlier
sprinkling begins, the more bud development can be delayed.

Early blooming cultivars and species are more likely to benefit
from evaporative cooling than are late blooming cultivars and
species because of the greater frost hazard to the former.

An adequate water supply is of primary importance in
determining feasibility of evaporative cooling. Minimum require-
ments for freeze protection are 3 . 8 - 5 . 1 mm/hr . With evaporative
cooling, effective delays have been achieved*with 1.8 mmvTun
likewise, the cycling used in evaporative cooling allows recharg-
ing of the water source as well as simultaneous coverage of 2
or more blocks of trees. In contrast, with sprinkling for
freeze protection, water must be applied continuously as long as
the temperature remains below freezing. Often damage occurs to
tree structure, and the excessive amounts of water applied may
interfere with orchard practices. Evaporative cooling systems
are less expensive than other fOrms of frost protection and.mdght

be adapted for pesticide or fertilizer application.

42

BIBLIOGRAPHY

43

Bibliography

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Anderson, G. L. Ashcroft, E. A. Richardson. 1974.
Preventative freeze protection by preseason sprinkling
to delay bud development. ASAE Paper No. 73-231,
Amer. Soc. Agr. Engr., St. Joseph, MI

Anderson, J. L. 1977. Persoral communication.

Bauer, M., C. E. Ctaplin, G. W. Schneider, B. J. Barfield, and
G. M. White. 1976. Effects of evaporative cooling during
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Bennett, J. P. 1950. Temperature and bud rest period. Effect

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Ciessness, J. L., and H. J. Brand. 1969. Sprinkling to reduce
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44

45

Coville, F. V. 1920. 'ITe influelce of cold in stimulating the
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Crossa-Raynaud, P. 1955. -Effets des hivers doux, sur le
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Gilbert, D. E., J. L. Meyer, and J. J. Kissler. 1970. Evaporation
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, 1977. Personal communication.

 

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