Fluoride Investigations
at the Mid-Columbia
Experiment Station,
1961-1979
r``
fi
r`'c'J
'Pk 1987
N
ON Sr
OREGON
f
.
8'S1TY
.
q
Technical Bulletin 143
AGRICULTURAL
EXPERIMENT
STATION
Oregon State
University
Corvallis, Oregon
April 1982
AUTHORS: T. J. Facteau, associate professor of horticulture, E. E. Rowe, professor
of statistics, and W. K. Mellenthin, professor of horticulture, Oregon State University.
CONTRIBUTORS: Departments of Horticulture, Agricultural Chemistry, and Statistics, Oregon State University.
Contents
Introduction ............................................................................................................
5
Methods .................................................................................................................
1961 season ........................................................................................................
1962 season ........................................................................................................
1963 season ........................................................................................................
6
Dilute hydrofluoric acid sprays, 1973-1979 .................................................................
Fluoride fumigation experiments, 1966-1%9 ...............................................................
Fluoride fumigation experiments, 1970-1972 ...............................................................
Fluoride fumigation experiments, 1975-1978 ...............................................................
7
6
E
7
E
E
9
Results ................................................................................................................... IC
1961 season ........................................................................................................ IC
1962 season ........................................................................................................ 12
1963 season ........................................................................................................ 13
1973-1979 .......................................................................................................... If
Fluoride fumigation experiments, 1966 ...................................................................... IS
Fluoride fumigation experiments, 1967 ...................................................................... 19
Fluoride fumigation experiments, 1968 ...................................................................... 19
Fluoride fumigation experiments, 1969 ...................................................................... 22
Fluoride fumigation experiments, 1970-1972 ............................................................... 24
Fluoride fumigation experiments, 1975-1978 ............................................................... 29
Discussion ............................................................................................................... 31
Fruit set ............................................................................................................ 31
Pollen germination and pollen tube growth ................................................................. 32
Fluoride symptoms .............................................................................................. 32
Growth ............................................................................................................. 33
Fruit firmness ..................................................................................................... 33
I iter2turp Ci}Pd
........................................................................................................
'td
Fluoride Investigations at the
Mid-Columbia Experiment Station: 1961-1979
T. J. Facteau, K. E. Rowe,
and W. M. Mellenthin
ABSTRACT
Fruit set of sweet cherries was reduced if sprays containing fluoride
(sodium or ammonium fluoride or hydrofluoric acid) were applied during
anthesis. Sprays applied at other times during the fruit-growing season caused
fruit and leaf symptoms, depending on the concentration of fluoride, but no
reductions in fruit set. Symptoms of fluoride toxicity were blackening, shrivel-
ing, and "dimpling"; increased firmness of the stylar end of the fruit and
marginal necrosis; interveinal chlorosis, cupping, reduced leaf size, and a loss of
leaf tip. Similar responses were found, both with respect to fruit set and
symptom expression, when sweet cherry limbs were enclosed in mylar cages and
fumigated with gaseous hydrogen fluoride for varying periods of time at
varying air fluoride concentrations. Fruit set reduction was linearly related to
increasing dose of fluoride (expressed as hours exposure times concentration of
fluoride in µg/m'). Germination of pollen and growth of pollen tubes were
found to be inhibited by fluoride.
Growth of fruit and vegetative tissues was influenced only at the higher
levels of gaseous fluoride tested (4-6 )Ag/m') and generally after whole season
treatment.
Key words: Fluoride, sweet cherry, percent fruit set, growth, pollen
germination, pollen tube growth, symptoms.
INTRODUCTION
Atmospheric hydrogen fluoride (HF) has been shown to be toxic to many plant
species. Usually fluoride (F) injures plants (Treshow and Pack, 1970), but F has
been shown to decrease plant growth (Brewer et al., 1960a, 1960b, 1967b, 1969b;
Leonard and Graves, 1966; Treshow et al., 1967) and also to increase growth
(Treshow et al., 1967; Treshow and Harner, 1968; Brewer et al., 1960a, 1967b;
Hitchcock et al., 1963, 1971). Weinstein (1977) pointed out that these growth
increases may not show that F is beneficial to plants since some of the growth
responses were "more twiggy growth in rose and citrus or taller, but not necessarily
sturdier bean and tomato plants." Fluoride adversely affected plant fruiting
(Leonard and Graves, 1966; Pack and Sulzbach, 1976; DeOng, 1946; Hitchcock et
al., 1963; Brewer et al., 1967a, 1969a) or had no effects (Hitchcock et al., 1964).
Fluoride interfered with pollen germination and pollen tube growth of sweet cherry
(Lai Dinh et al., 1973; Facteau et al., 1973), although the exposure times and
concentrations where there are significant reductions are not clear. Lai Dinh et al.
(1973) reported that 97 µg F/m' reduced sweet cherry pollen germination after
24-hour exposure and, after 48 hours, reduced both germination and tube growth.
Facteau et al. (1973) reported a linear relationship between increased3F dose (hours
exposure times F concentration) and decreased pollen tube growth and germination
and stated that at 2.5 µg F/m' in 1970 and 3.7 µg F/m' in 1971, there was little or no
pollen tube growth. Since pollen tube growth is essential for fruit set in sweet
cherry, this could reduce fruit set. Facteau and Mellenthin
(1976) observed a
positive correlation between fruit set and distance from an aluminum reduction
plant. Direction was also an important predictor variable in that survey. Vegetative
growth also was related to distance, direction, and foliar F levels in that study. Lai
Dinh et al. (1973) reported that sweet cherry fruit set was not influenced by
concentration of 2.5 µg F/m' in the immediate vicinity of a hydrofluoric acid
factory. MacLean et al. (unpub. data, reported by Weinstein, 1977) reported that a
high F dose reduced sweet cherry pollination. This report presents results from F
spray experiments (1961-1963, 1973-1978) and gaseous F fumigation experiments
(1966-1972) conducted at the Mid-Columbia Agricultural Experiment Station,
Hood River, Oregon.
METHODS
1961 season
Ten pairs of `Napoleon' sweet cherry trees were selected for uniformity of age,
and distance from a pollenizer. The trees were selected from an orchard in
Mosier, Oregon, which was free from any F pollution. The orchard is approximately 10 miles west of The Dalles. The predominant wind pattern was either calm or a
westerly wind. Sprays containing 500 parts per million (ppm) fluoride (NH.F) were
applied with a DeVillbus paint sprayer and gun (Model PO-502 and PCN-501,
respectively) at a pressure of 40 pounds to runoff. The sprays were applied to one
tree of each pair at approximately 10-day intervals from prebloom (popcorn stage,
when white is showing on the developing flowers) to fruit harvest. The trees were
sprayed seven times throughout the season, with only one spray applied during
bloom time.
size,
On another set of two `Napoleon' trees, selected limbs were thinned and
emasculated before blossoming. There were three limb replicates per tree. Care was
taken to remove all opened flowers and those too early to be receptive to pollen. The
remaining flowers were sprayed with a solution of NH.F at 0 (water), 2.5, 5, 10, 25,
50, or 100 ppm F with a fine mist atomizer. These flowers were covered and hand
pollinated 24 hours later with `Black Republican' sweet cherry pollen. The pollen
was collected by suction with a Neptune pump and glass vial. It was dried for 5 days
in a desiccator and kept frozen until used. Viability tests were carried out on an agar
media (Schuster, 1925) to insure that the pollen was suitable. Fruit counts were
started at shuck stage and made every week until harvest.
Samples of the `Black Republican' pollen collected were germinated on agar
media (Schuster, 1925) containing varying (zero to 100 ppm) amounts of F. NH.F
was the source of F. Ten microscope fields (100x) were examined on each agar plate.
1962 season
Twelve mature `Napoleon' trees were selected for uniformity in each of 10
orchards (eight in The Dalles and two in Mosier). The trees were sprayed at full
bloom, postshuck, and about 10 days after postshuck with NaF sprays ranging in
concentration from 0 to 4,000 ppm F, with three tree replicates at each F level. Two
groups of control trees also were selected in each orchard. One set of three trees
received water from a local water supply and the second set (three trees) was sprayed
with a NaCl solution in which the Na level was equal to the highest Na concentration
in the F sprays. Symptoms were noted periodically and data on fruit yields, set,
average cherry fresh weight, total acids, soluble solids, and fruit firmness were
taken at fruit maturity. Flower counts were made at full bloom and fruit counts
were made at harvest. Approximately 100 cherries were picked at random for the
fruit data. Total acids were recorded as milligrams malic acid per 100 milliliters
juice. Soluble solids were taken with a Toko hand refractometer, and pressure tests
on the stylar end were recorded with a Chattilion pressure test gun with I/ 16-inchdiameter points. Spring tension was adjusted to take in the range of firmness found
in the fruits, so the readings were in pressure units.
Tree yields were collected again in 1963. Fruit samples were collected from the
high F treatment and the water check to determine fresh fruit weight and firmness.
Two limbs per tree were selected and 30 to 35 flowering buds were counted for fruit
set data.
1963 season
Individual limbs were used in 1963 in The Dalles because of the large number of
replications (25 limbs for each treatment). Uniform limbs were selected on the
south side of the `Napoleon' trees, and the trees were grouped in turn to reduce
possible variability caused by soil type, moisture, frost injury, and fertility. NaF
was used as the source of F. The sprays were applied as in 1961 and 1962 during
bloom, which was determined to be a 12-day period beginning with the tight
popcorn stage. Experiments conducted through the bloom period were: (1) Six
timings of single applications of 50 ppm F throughout bloom and 2-day intervals,
(2) three single applications of 25 ppm F spaced through bloom, (3) three single
applications of water plus unsprayed limbs to serve as controls, and (4) four timings
throughout bloom of five sprays per day of 10 ppm F. In addition to the bloom
sprays, limbs were sprayed daily with 50 ppm F at 10-day intervals (treatments were
50 ppm F once per day for 10-day intervals) throughout the growing season.
Approximately 100 flowers were counted on each limb on 2-year-old wood for fruit
set data. New shoot growth was recorded for the limbs; fruit weight and firmness
were measured on mature fruits.
Another set of `Napoleon' sweet cherry limbs was selected for uniformity in a
Hood River orchard. Treatments consisted of sprays of 25 ppm F and water applied
before and after pollination. Approximately 50 flowers per limb were emasculated
during the popcorn stage and were hand pollinated 24 hours after or before the
treatments were applied. Percent fruit set was taken on the emasculated flowers.
Each treatment was replicated 10 times.
Dilute hydrofluoric acid sprays, 1973-1979
Dilute hydrofluoric acid sprays were applied to 20-year-old (in 1973) 'Napole-
on' sweet cherry trees during anthesis and at irregular intervals each of seven
successive growing seasons at the F spray concentration listed in Table 9. Three
(1973, 1974), 10 (1975, 1976), and 30 (1977, 1978, 1979) single-tree replicates were
used at each spray level. Trees receiving the two low and two high F sprays (1976)
were combined into two treatments in 1977. Four limbs per tree (one each NE, SE,
NW, SW quadrant) were tagged and measured for linear growth, flower buds,
flowering spurs, total spurs, flowers, and fruit at appropriate times during the
growing season (limb set A). Data were collected annually on 2-year-old wood.
Initially, limbs were selected at approximately 240 cm above ground level. Starting
in 1977, more vertical limbs were selected at approximately 300 cm above ground
level, and measurements were taken in 1977, 1978, 1979, and 1980 (limb set B). In
1973, 1975, and 1976, 50 fruit were sampled from each limb (or nearby limbs) and
firmness (Hunter mechanical force gauge, 0 to 500 grams) and fruit weight were
recorded. Leaves were sampled in early September and analyzed for F 'content
(Galley et al., 1969).
Fluoride fumigation experiments, 1966-1969
Fumigation trials were conducted in Mosier, Oregon, on `Napoleon' sweet
cherry limbs for various durations of exposure and concentrations of gaseous F
from 1966 to 1969. Treatments consisted of levels of F (0 to 20 µg F/m') for
periods encompassing the stages of prebloom, full bloom, shuck stage (when the
enlarging fruit sloughs off the remaining flower parts), and harvest. Treatment
duration and F concentrations are shown in the results section for each year.
Hydrogen fluoride was generated using the system of Hill et at. (1959). Briefly, air
at varying rates was passed through heated solutions of hydrofluoric acid of
varying concentrations to establish the desired air F concentrations. Air was
circulated through the chambers (similar to those described by Mellenthin and
Bonney, 1972, except that cages used were stationary) at approximately one
chamber volume charge per minute. Air F levels were sampled by drawing air at one
m'/hr through an impinger (tested against a Greenburg-Smith impinger and gave
similar results). Fluoride levels were analyzed by a technicon distillation system
(1966-1968, Wernstein et a/., 1963; 1969-1978, Cralley et a/., 1969). Generally,
measurements were made each year of percent fruit set, fruit firmness, soluble
solids, acidity, and weight, and observations were made of leaf and fruit condition.
Cages were opened from approximately 10 a.m. to 4 p.m. each day (6 hours) during
anthesis in 1966 and 1967 to provide for bee activity and pollination. Limbs were
not fumigated during these hours. Approximately 100 to 200 flowers were hand
pollinated in 1968 and 1969 and used for fruit set measurements. Pollen was
collected by suction from each caged limb on several days in 1968 and 1969 (see
Table 13 for lengths of fumigations and F concentrations) to test the effects of F on
pollen germination.
Fluoride fumigation experiments, 1970-1972
Fumigation experiments were conducted on `Napoleon' sweet cherry limbs in
Mosier, Oregon (1970-1971) and The Dalles, Oregon (1972). Fumigation treatments in 1970-71 were 2, 4, or 6 hours duration at air F concentrations from 0.3 to
67.8µg F/m' during anthesis and 4 hours duration at the same air F concentrations
approximately 2 weeks after bloom. Fumigations in 1972 were at air F concentra-
tions from 0.8 to 6.3 µg F/m' for durations of 21.5 to 26.7 hours during anthesis.
The number of limbs treated during anthesis was 182, 215, and 48 for 1970-1972,
respectively. The number treated during shuck was 20 and 60 for 1970 and 1971,
respectively. An additional 61 limbs were caged in 1972 for approximately 2, 4, 6, or
24 hours, but were not fumigated in an attempt to study the response of fruit set to
caging alone.
Fumigation chambers were similar to those described by Mellenthin and
Bonney (1972) except no temperature modification equipment was used. Cages
were moved at random onto limbs judged to be in full bloom. Fumigations were
conducted on 9 days in both 1970 and 1971 and on 7 days in 1972.
Hydrogen fluoride was generated from iced containers (Thompson and Ivie,
1965) and introduced into the incoming airstream. Air was circulated through the
cages at approximately one chamber volume charge per minute. Air F levels were
sampled by drawing air at one m'/hr through NaOH-treated filter papers for the
duration of each fumigation (Mandl et al., 1971). Papers were eluted with 10 ml of
IN HZS04, and F contents were determined according to Cralley et a!. (1969).
Percent fruit set was determined for the three seasons on 300 to 400 flowers per
limb. Fruit counts were made 2 to 3 weeks before commercial harvest. Counts on an
adjacent uncaged limb served as a covariable of fruit set in the absence of treatment.
Distance to the nearest pollenizer tree (in relative units) was also recorded. Because
of a severe freeze (-3.3°C) just before bloom and several subsequent frosts in
1972, additional measurements were made. These were maximum and minimum
temperatures during fumigation, height above ground of fumigated and nonfumigated limbs, and percent of frost-damaged flowers.
In 1972, approximately 0.5 meter of limb was covered with cheesecloth before
bloom. Before fumigation, the cheesecloth was removed, and flowers were hand
pollinated and sampled to ascertain that no pollen had germinated (0 day).
Seventy-two hours later, regardless of the duration of fumigation, flowers were
again sampled. Flowers were fixed in formalin, acetic acid, and ethanol (3:1:1), and
pollen tube lengths were determined and analyzed by methods previously described
(Facteau et al., 1973).
Multiple linear regression analyses and analyses of covariance were used to
study the effects of day of treatment, distance to pollenizer, limb height, nonfumigated fruit set, concentration of F, and duration of exposure on the percent fruit set
of treated limbs. These statistical techniques also were used to study the effects of
caging on fruit set and the effect of F on pollen tube lengths.
Fluoride fumigation experiments, 1975-1978
Starting in the spring each year, fall-budded `Napoleon' trees were fumigated
constantly with selected air F concentrations in
1975,
1976, and 1978. Trees
fumigated in 1975 were continued through to fall 1977 (two growing seasons). Trees
fumigated in 1977 were 2 years old and had not been previously treated with F.
Fumigations were conducted in three 300 x 300 x 240 cm, open-topped mylar cages
in a lath house. Air was introduced on one side at 2,832 liters per minute and
dispersed in the cage at ground level through a Y-shaped, 4-inch, flexible plastic
drainfield tube. Two squirrel cage blowers (2,832 liters per minute) provided mixing
within each cage. Gaseous HF was introduced into two of the cages by the incoming
airstream, using the technique of Hill et al. (1959). Air F concentrations were varied
by using different hydrofluoric acid concentrations and airflow rates through the
generation system. Air F levels were sampled 91 cm above the ground twice each
week using NaOH-treated filter papers (Mandl et al., 1971), and F levels were
analyzed using the micro-distillation technique (Cralley et a!., 1969). Terminal
growth on the central leader and each side shoot was measured after cessation of
growth each year. Leaves were sampled in September, washed, and analyzed for F
content (Cralley et al., 1969). Trees were grown in one-gallon metal cans (1 /3 soil,
1/3 peat, and 1/3 sand), using 7 to 15 trees at each F level.
RESULTS
1961 season
Ammonium fluoride sprays containing 500 ppm F applied at approximately
10-day intervals from popcorn to fruit harvest had no significant effect on percent
fruit set, percent No. 1 size cherries (26/32), average pit weight, or total number of
pounds fruit per tree even though the F-treated trees showed a trend toward reduced
fruit set and smaller cherries (Table 1). The F sprays significantly reduced the
average fresh fruit weight, and the fruits developed a small, crescent-shaped dimple
or depression just before harvest. This dimple was very shallow (1 to 2 ml) and
appeared only on the stylar end of the cherry.
Table
1.
Effect of ammonium fluoride sprays on `Napoleon' sweet cherries,
(Mosier, Oregon, 1961)
Treatment
Average
yield
Fruit parameter
Avg. fresh
Avg.
Avg. #I size
cherry wt.
(lbs)
(g)
451
5.1362
412
5.716
fruit set
(%)
cherries
Avg. pit
wt.
(%a)
(g)
16.68
18.91
64.56
79.56
0.258
0.265
7 sprays of 500 ppm
NH,F applied at
10-day intervals'
Controls
Averages of 10 trees, sprays applied at 10-day intervals from popcorn to fruit harvest.
2 Significant at 5% level.
Sprays of 0, 2.5, 5, 10, and 25 ppm F on emasculated flowers which were hand
pollinated 24 hours later did not significantly reduce fruit set. There was a
significant reduction in percent fruit set with spray concentrations of 50 and 100
ppm F (Fig. 1). This significant drop appeared during the fourth and fifth week
from bloom, which was close to the middle of the cherry-growing season.
`Black Republican' pollen germinated on agar containing increasing concentrations of F resulted in a reduction of germination with an increase in F
concentration up to 75 to 100 ppm (Fig. 2).
25
5
1
0
10
20 30 40 50 60 70 80 90
100
ppm F, SPRAYED AS NH4F
Effect of increasing concentration of fluoride sprays on percent fruit set of
`Napoleon' sweet cherries, M. Sprays were applied at popcorn stage to emasculated
Figure 1.
flowers which were hand pollinated 24 hours later.
z
0
a 30
z
02 25
W
0
z
W
20
-J
15
0n.
I0
W
5
W
Q.
0
10
20 30 40 50 60 70 80 90
100
ppm F IN AGAR AS NH4F
Figure 2.
Effect of fluoride on germination of `Black Republican' sweet cherry pollen,
1961.
11
1962 season
Data for the 1962 season are presented in Table 2. Total fruit yields were
significantly reduced by the three F sprays. The reduction in yield was found at all
levels of F treatments as well as the NaCI treatment. With each increase in F
concentration, the total yield per tree was reduced, and this same pattern was
present in the weight per 100 fruits. A significant reduction in percent fruit set was
found at the highest spray treatment. The NaF sprays also significantly increased
cherry firmness at the stylar end and the pH of the cherry juice. There was a
decrease in milligrams total acid as the F concentrations increased.
Table 2. Effect of sodium fluoride on production and quality of
`Napoleon' sweet cherries, (Mosier, Oregon, 1962)'
Yield
(lbs/
Fresh
fruit
Total
Fruit
acids
Soluble
set
(mg/ 100
solids
tree)
(g/100
fruits)
(%)
pH
ml)
(%)
Firmness
(g)
Water check.........
400.1
654.5
14.32
3.85
14.98
113.2
NaCl ..................
332.3
335.3
267.3
211.8
14.90
16.87
3.85
3.85
15.12
14.50
127.2
189.7
14.29
3.90
3.90
15.57
178.7
623.9
623.0
593.5
590.7
556.5
14.36
241.6
263.9
299.9
59.8
34.6
0.73
16.8
Treatment
500 ppm F............
1,000 ppm F
2,000 ppm F
4,000 ppm F.........
LSD (.05).........
8.90
3.92
956.8
954.2
947.9
938.2
922.3
926.3
3.3
0.03
24.8
12.48
15.10
' Three sprays were applied at full bloom, postshuck stage, and approximately 10 days after postshuck
stage.
Table 3. Fluorine content of `Napoleon' sweet cherry leaves from
fluoride spray plots, (1962)'
Treatment
NaF (ppm F in spray)
Plot
500
A
403'
B.
368
Average......
C .................
D .................
E ..................
Average......
F ..................
G .................
H .................
386
919
531
Average......
All averaged....
'
262
234
247
248
278
265
232
258
286
4,000
NaCl2
Water
1,154
2,531
37
32
1,631
1,394
2,951
2,741
37
968
958
2,082
1,853
52
45
756
1,964
1,966
57
51
990
....
40
49
1,000
2,000
778
1,059
580
547
553
378
370
891
36
29
26
....
53
1,375
33
....
331
644
738
568
1,078
360
650
1,148
60
47
70
60
572
927
1,853
47
43
Average of three replications.
Sodium chloride spray at same sodium content as the highest sodium fluoride treatment.
' Fluoride content as ppm dry weight.
Fluoride contents of the sweet cherry leaves are presented in Table 3. These
data have been grouped in three lots based on the level of leaf F content. The trees
that were considered to be the most vigorous had the lowest leaf F concentrations,
while the least vigorous ones (trees showing the greatest amount of winter injury),
were the highest in F concentration. This might have been a reflection of leaf size,
but also may suggest that vigorous trees accumulate less F.
Trees given a high F concentration had severe foliage burn and necrotic
current-season terminals. The foliar burn was also present on the NaCI-treated
trees. Lower F concentration treatments resulted in a mild interveinal chlorosis leaf
pattern after the second spray. Fruit injury was also found after the second spray, as
immature fruits turned brown and in most cases abscised before harvest. A
depression, or dimple, on the stylar end of the cherry was found only on mature
fruits.
Data taken in 1963 on the same trees sprayed in 1962 are presented in Table 4.
These data show the same trend in average tree yields as was found in 1962.
However, there was no significant difference with respect to yield. There was also
no apparent difference in fruit set, weight, or firmness.
Table 4. Effect of a previous year's sodium fluoride spray
treatment on `Napoleon' sweet cherries'
Avg. tree
yields
Fruit set/
flowering bud
Fruit wt.
(g)
Firmness
(g)
Water ............................
NaCl .............................
500 ppm F .......................
0.62
0.59
7.13
90.56
0.65
327.7
1,000 ppm F ....................
0.71
317.9
F ....................
0.63
4,000 ppm F ....................
0.65
Treatment
2,000 ppm
(Ibs)
344.0
308.5
310.0
7.10
96.58
290.8
' Three sprays were applied at full bloom, postshuck stage, and approximately 10 days after postshuck
in 1962.
1963 season
A summary of the data on the effects of F sprays on `Napoleon' cherries at
various times during the bloom period is presented in Table 5. There was no
significant difference in fruit set with respect to bloom stage (compared to any of
the control treatments). Fruit set tended to be lower the closer each treatment was
applied to full bloom. Since the limbs that were selected to receive a particular spray
treatment were chosen before bloom, not all single-treatment limbs were in the
same stage of bloom when the sprays were applied. Therefore, the data were
separated and analyzed according to bloom stage, regardless of treatment applied.
Table 6 shows that there was a significant decrease in fruit set in treatments applied
at stages one and three and a reduction in set as bloom advanced. There was no
significant difference in shoot growth, average fresh fruit weight, or firmness when
the data were analyzed during bloom period or when grouped into bloom stage.
13
Table 5. Effect of sodium fluoride sprays at various intervals
during anthesis on `Napoleon' sweet cherries, (Mosier, Oregon, 1963)
Treatment
Fruit set
Timing
('o)
Shoot growth
(cm)
Fruit wt.
(g)
Firmness
(g)
1 application of 50 ppm F
Early popcorn
Late popcorn
12.92
15.16
13.53
15.69
13.48
5
7% flowers open
22% flowers open
30% flowers open
6
Full bloom
7
Popcorn
8
25% flowers open
14.69
13.77
9
Full bloom
12.25
I
2
3
4
120.21
17.56
6.84
7.06
7.28
12.26
16.32
7.18
12.00
17.38
6.96
117.68
114.38
11.30
15.73
7.21
111.52
15.64
17.34
7.04
112.28
7.11
109.62
14.29
7.13
114.68
7.11
107.72
6.97
7.05
6.93
110.13
123.77
116.60
I application of 25 ppm F
I application of H, 0
10
Popcorn
14.25
11
36% flowers open
14.26
15.92
15.04
12
23
Full bloom
12.42
13.89
16.28
14.46
13
14
15
Early popcorn
15.95
16.14
6.83
111.30
Late popcorn
16.87
15.54
7.21
108.58
14% flowers open
15.30
16.78
7.27
109.93
16
32% flowers open
10.93
16.46
7.44
111.24
4.72
3.30
.44
9.92
Untreated control
113.76
109.59
5 applications of 10 ppm F
LSD, 5%
Table 6. Effect of sprays of sodium fluoride at different bloom stages on fruit set,
weight, firmness, and shoot growth of `Napoleon' cherries,
(Mosier, Oregon, 1963)'
Shoot growth
(cm)
Fruit wt.
(%)
(g)
Firmness
(g)
15.08
15.51
6.94
116.81
12.98
16.76
7.17
113.42
10.61
15.82
7.16
112.23
Fruit set
Bloom stage
Prebloom .......................
1 - 50% flowers
open ..........................
51016 flowers open
to postbloom ................
LSD, 5% .....................
3.5
' Data were taken from the fluoride spray concentrations listed in Table 5. All single-treatment limbs
were not in the same stage of bloom when treatments were applied. Data are analyzed in this table
according to bloom stage, regardless of fluoride treatment applied.
14
Spray treatments throughout the growing season. Fruit set was reduced by
sprays during bloom (Table 7), but not at any other time during the season.
Although there were no responses in shoot growth or total acids, fresh fruit weight
was reduced by sprays during the growing season. Fruit firmness was increased with
sprays applied during bloom. During the development and growth of the cherry
fruit, F treatment resulted in an increase in firmness with advancement in maturity
(Fig. 3).
Pollination sprays. `Napoleon' sweet cherry flowers sprayed with 25 ppm F
before pollination had reduced fruit set (Table 8). Fruit set on flowers sprayed 24
hours after pollination was also reduced, but the reduction was not statistically
significant.
Table 7. Effect of daily sprays of 50 ppm fluorine for 10-day intervals at various stages
during the growing season on 'Napoleon' sweet cherries, (Mosier, Oregon, 1963)
Developmental
stage
Fruit set
(%)
Shoot
growth
Fruit
weight
Firmness
Total
acids'
(cm)
(g)
(g)
(mg)
15.96
6.52
127**
386
14.22
6.71
120*
397
14.28
5.95**
161**
397
14.84
5.88**
210**
402
14.09
15.23
6.22**
5.64**
6.93
242**
279**
109
413
Tight popcorn to
full bloom ................... 5.23**2
Full bloom to
shuck ......................... 7.95*
Shuck to pit
hardening ....................12.08
Pit hardening to
final swell .................... 13.42
Final swell to
white ..........................15.86
Whitetobrine ..................13.92
Unsprayed control ............ 13.89
14.46
388
394
Mg total acids/100 ml juice.
Statistically significant from the unsprayed control at I % (**) and 5% (*) levels.
Table 8. Effect of aqueous fluoride sprays before and after pollination on fruit set of
'Napoleon' sweet cherries (Hood River, Oregon, 1963)
Fruit set
Spray
25 ppm F ................................................
HZO ......................................................
25 ppm F ................................................
H:O ......................................................
Timing'
(%)
After pollination
After pollination
Before pollination
12.2
16.2
Before pollination
LSD, 5%
19.1
7.9
7.0
In each treatment there was a period of 1 day between the time limbs were pollinated and sprayed.
300
FIRMNESS 3.4 (DAYS) + 89.1
r- .9753
200
100
5
20
40
60
DAYS FROM FULL BLOOM TREATMENT APPLIED
Figure 3. Effect of sprays of 50 parts per million fluoride throughout the growing season
on fruit firmness of `Napoleon' sweet cherries, 1963. Treatments were divided into 10-day
intervals and sprays were applied daily during each 10-day period. Points represent the
midpoint, from bloom, of that treatment.
1973-1979
Sprays of dilute hydrofluoric acid caused no reduction in fruit set in 1973-1976
(Table 9, data from 1973 and 1974 are not presented). F sprays applied in 1977,
1978, and 1979 resulted in reductions in fruit set each year on limb set B. Lack of
response on limb set A may be a result of fewer tree plots (3 vs. 30) or because of
variation in stage of bloom of individual limbs. No attempt was made to group the
limbs into bloom stage as was done in 1963. Other factors, such as temperature,
could have influenced the fruit set response.
Fruit responses. Applications of HF did not affect fruit weight in 1973-1976.
Fruit firmness on the stylar end was increased by the two highest F sprays in 1975
and 1976 (Table 10).
Growth. The two highest F spray concentrations resulted in increased growth
on limb set A in 1976 (1975 growth) (Table 10). F sprays of approximately 40 ppm
resulted in increased growth on limb set B in 1979 and 1980 (Table 9). No
differences were found in 1975, probably because vigorous limbs had been chosen.
However, these limbs showed a gradual reduction in terminal growth of both F and
non-F spray branches in subsequent years, with the greatest decrease in the
controls. A similar pattern was found in limb set A (data not shown for 1973 and
1974). The numbers of flower buds, flowering spurs, total spurs, and flowers
generally increased as the F spray concentration increased. These changes probably
10.2
32.3
33.8
0.18 ±0.02
41.94±1.22
0.938
Probability
36.9
12.6
95.9
10.6
0.997
7.9
0.994
35.1
17.1
0.989
Probability
0.999
11.8
0.19±0.01
0.956
45.29±0.99
8.4
0.975
Probability
5.8
131.2
11.4
40.3
23.4
112.8
11.0
9.6
10.4
37.8
120.0
116.9
107.3
28.4
13.7
0.993
66.5 b
23.3
13.7
13.2
10.9
7.2
10.8
10.5
40.8
3.6
43.2
38.7
23.3 a
33.3 a
35.0 a
79.6
97.9
0.19±0.01
45.29±0.99
16.2
5.7
9.0
10.2
54.62± 1.77
3.5
5.7
11.5
2.5
8.8
8.2
5.8
11.00±0.62
23.71±1.41
Probability
35.0
5.6
5.8
5.2
2.6
9.7
29.9
27.1
16.5
16.1
67.3
54.2
standard error of the mean.
Probability values are for F or T-tests. Means separation by LSD, 5% 1 evel.
' Only 0 and 50 ppm F spray treatments were applied. Trees from treatments 0 and 15, and 30 and 50 were combined.
Data from 1980 are classified by results of 1979 spray concentrations.
27.6
21.2
22.4
23.6
50.8
43.1
55.7
55.5
0.991
21.1
0.999
0.999
34.2
0.999
26.9
36.2
B
41.6
25.9
30.7
32.6
22.2
30.2
34.8
35.0
29.3
15.6
67.1
6.7
21.3
4.3
28.4
30.4
19.5
58.4
69.2
22.8
33.5
16.2
21.2
58.7
A
5.7
6.9
B
Fruit set
(%)
5.9
A
Fruit
18.3
7.4
7.7
B
A
B
A
8.6
39.4
B
Flowers
A
B
19.6
A
4.4
3.7
0.963
Probability
0.20 ± 0.03
8.5 b
11.4 b
5.4 a
38.14± 2.35
5.8 a
0.23 ± 0.03
11.00±0.62
23.71 ± 1.41
0.927
Probability'
0.21 ± 0.02' 8.8
14.61 ±0.47
8.3
29.53 ± 0.80 10.9
49.01 ± 1.82 14.8
concn.
B
A
F spray
Flower buds
Limb set'
Total
spurs
Flowering
spurs
All data, except for growth values, are from 2-year wood. Growth values are for previous year's .growth.
Limb set A was original limbs counted. Limb set B was a new selection of more vigorous limbs.
19806
1979
1978
1977'
1976
1975
Year
Growth yr.
prior (cm)
Table 9. Growth and fruit set of `Napoleon' sweet cherry trees on 2-year wood in response to dilute hydrofluoric acid sprays
Table 10. Fluoride concentrations in dilute hydrofluoric acid sprays, number of sprays,
fruit weight and firmness, and leaf F levels for `Napoleon' sweet cherries, 1973-1979
Year
1973
F spray
concn.
(ppm)
0.20±0.011
Fruit
Fruit
weight
Leaf F
sprays
firmness
(g)
(g)
(ppm)
21
No.
215
5.6
8.4
2.15±0.05
230
5.5
10.3
4.26±0.09
5.7
13.1
5.6
10.4
5.3
13.9
10.03 ± 0.36
215
215
234
226
5.5
10.0
14.70±0.34
217
5.4
17.1
6.45 ±0.12
8.34± 0.24
1974
0.20±0.01
18
7.2
9.4
1.85 ±0.06
6.7
7.6
3.81 ±0.10
6.36±0.25
7.8
7.7
7.4
7.7
6.4
6.8
7.1
7.0
8.9
24.4
32.8
6.6
4.6
7.63±0.34
9.11 ±0.23
12.85±0.45
25.42±0.74
42.11±0.81
1975
0.21±0.02
15
14.61 ±0.47
29.53 ±0.80
49.01±1.82
Probability'
1976
0.23 ±0.03
6.5
7.5
6.8
13.0
274 b
6.6
19.3
242 a
6.3
7.4
6.2
12.8
23.71 ± 1.41
250 a
258 b
6.6
24.3
38.14±2.35
260 b
6.9
42.2
16
Probability
977
262 a
261 a
290 b
0.962
11.00±0.62
1
0.20±0.03
0.995
24
54.62± 1.77
1
1
978
979
10.5
12.0
16.0
5.3
41.0
0.18 ±0.02
41.94± 1.22
9
0.19±0.01
45.29±0.99
8
4.5
14.2
± standard error of mean.
Probability values are for F tests. Means separation by LSD, 5'o level.
7.0
10.2
reflect differences in growth. No visible symptoms of F damage to foliage or fruit
were observed at any time during 7 years of treatment.
Fluoride fumigation experiments, 1966
Results from the 1966 fumigation experiments are presented in Table 11. It
proved difficult to obtain the desired air F concentration within a given cage on a
daily basis and to have replicated levels on separate limbs. Nevertheless, symptoms
of F toxicity were apparent. There was no identifiable effect on fruit set, weight, or
soluble solids at any of the time-concentration combinations. Fruit resistance to
puncture at the stylar end was increased where the air F concentrations were greater
than the controls for the longer duration fumigations. The highest concentration
and longest duration cages (numbers 14 and 31) had very high firmness readings,
and fruits in these units exhibited severe stylar-end shriveling and blackening. Fruit
in cages where the air F concentrations were greater than one µg F/m' after bloom
exhibited a dimpling, or hooking, of the stylar end. Foliar interveinal chlorosis
appeared during the 30 days after bloom and was most severe on the longer
duration, higher F concentration cages.
Fluoride fumigation experiments, 1967
Results from the 1967 fumigation experiments are presented in Table 12.
Because of the need for more replicates, treatment durations were reduced to three
(popcorn to full bloom, popcorn to harvest, budburst to full bloom) at air F
concentrations of approximately one µg F/m' plus a full season control. There were
no differences in percent soluble solids, fresh fruit weight, and percent fruit set,
although set tended to be lighter in the F cages. Fruit set was light in all instances,
only about 20 to 35 percent of what is generally considered a full crop (Westwood
and Stevens, 1979). Fruit firmness was higher in the F-treated fruit and generally
increased as the duration of fumigation increased. Interveinal foliar chlorosis was
observed on the budburst to harvest F treatment along with some slight fruit
dimpling.
Fluoride fumigation experiments, 1968
No fruit set data were taken from caged limbs used in 1968 because of severe
spring frost, but pollen germination percentages (Table 13), foliar F accumulation
(Table 14), and symptom expressions were noted. Germination of pollen was
reduced at an average air F concentration of 18.7 µg/m' fumigated from popcorn to
shuck stage. Accumulation of F in leaves was a function of time of exposure and
concentration. Leaf F levels generally decreased after cessation of fumigation,
probably because of growth dilution and/or loss of F through leaching (Brewer el
al., 1969b). Even though no fruit set data were taken, cages receiving the high F
concentrations (20.6 and 18.7µg F/m') had no fruit inside the cages, whereas there
was fruit in the other cages that received either less or no F. Symptoms of F toxicity
were very severe in the cages with highest F concentration, consisting of marginal
and tip necrosis, interveinal chlorosis, cupping, some defoliation, and smaller
leaves. New growth that occurred after cessation of fumigation appeared normal.
Symptoms at the levels of 4 µg F/m' were interveinal chlorosis on older leaves.
Popcorn to full bloom
Popcorn to full bloom
Full bloom to shuck
Full bloom to shuck
Full bloom to shuck
Popcorn to shuck
Popcorn to shuck
Popcorn to shuck
4
I
2
4
1
2
4
('o)
(µg F/m')
0.34:t 0.08'
0.84±0.10
32
20
24
36
1.74 ± 0.23
2.12 ± 0.20
2.34 ± 0.13
0.08± 0.04
9
12
18
11
2.72 ± 0.25
12.6
15.0
14.7
15.9
15.4
14.0
11.2
14.4
13.6
11.6
....
16.3
2.59±0.18
Limb died,
no fruit
9.2
1.12 ± 0.11
1.22 ± 0.12
0.05 ± 0.05
0.52 ± 0.07
0.05 ± 0.05
0.51 ± 0.05
0.05 ± 0.05
0.65 ± 0.18
1.48 ± 0.25
0.45 ± 0.03
0.20 ± 0.05
0.96 ± 0.17
0.43 ± 0.08
0±0
18.0
14.8
13.6
14.5
16.3
13.6
14.3
13.4
11.0
16.0
19.0
13.6
15.0
13.2
Soluble
solids
concn.
Actual F
0.32 ± 0.04
0.54 ± 0.06
0.18 ± 0.04
0.45 ± 0.16
2
28
13
33
7
27
10
30
14
4
23
6
1
22
16
15
19
35
Treatment
Cage
duration
no.
Popcorn to full bloom
8
2
I
Desired
F concn.
(µg F/m')
4/8
4/8
4/8
4/9
4/8
4/9
4/8
4/9
4/9
4.9
....
5/9
5/9
5/9
5/9
5/9
5/9
5/9
5/9
5/9
5/9
4/16
4/16
4/16
4/15
4/16
4/15
4/15
4/16
4/15
5/9
5/9
5/9
5/9
5/9
5/9
5/9
4/8
4/8
4/9
4/9
4/9
4/8
4/9
4/8
4/9
4/7
4/9
4/9
4/9
4/9
4/9
4/8
....
tion
stopped
started
Fumiga-
tion
Fumiga-
9.64
8.56
8.08
7.64
9.09
8.07
7.64
8.47
7.34
8.79
Weight
(g)
1.7
7.3
216'
11.8
3.8
8.9
8.8
4.4
20.5
5.4
9.4
....
8.2
21.7
5.6
4.4
7.66
7.05
8.54
8.39
7.60
7.71
7.50
8.72
7.64
9.00
....
7.44
6.73
9.80
8.51
16.06.72
10.37.46
1.6
11.8
3.9
4.3
5.1
0.9
3.7
I 0.6
5.2
6.9
I
(%)
Fruit set
244'
204'
227
208
175
194
192
248
253
....
220'
220'
207
215
200
175
131
188
178
164
152
218
197
139
162
186
Firmness
(g)
E
D
C
D
A
C
A
B
B
D
....
E
D
B
B
C
B
B
B
A
B
A
A
A
A
A
A
Chlorosis
rating'
Table 11. Treatment duration, fluoride concentrations, and fruit data from `Napoleon' sweet cherry fumigation experiment (Mosier,
Oregon, 1966)
A
A
0.95 ± 0.03
0.94 ± 0.01
0.78 ± 0.02
0 ± 0
19.1 ± 1.1'
94 ± 0
32 ± 0.6
94 ± 0
' ± standard error of the mean based on nine cages.
Averages of nine cages.
Popcorn to full bloom. .......
Budburst to harvest .... .......
Budburst to full bloom .......
Budburst to harvest .... .......
(days)
Duration
F concn.
(µg F/m')
Treatment
11.4 ± 0.7
10.7 ± 0.7
5.73 ± 0.2
186± 21.7
162 ± 5.1
13.4± 3.9
11.0 ± 0.4
5.32 ± 0.2
6.23 ± 0.2
233 ± 11.4
(%)
12.4 ± 0.5
(g)
6.57 ± 0.3
175 * 6.7
12.4 ± 4.0
11.1 ± 2.2
9.2 ± 1.8
Soluble
solids
Fruit
weight
Fruit
firmness
(g)
Fruit set
(%)
Table 12. Percent fruit set, fruit firmness, fresh weight, soluble solids, and duration and concentration of fluoride concentrations on
`Napoleon' sweet cherries (Mosier, Oregon, 1971)'
Chlorosis ratings were: A = none; B = slight; C = moderate; D = severe; E = very severe.
2 ± standard error.
' Fruit from these units showed "dimpling" at the stylar end.
5.7
7.80
8.31
6.7
193
205
6/21
6/21
4/12
4/12
0.05 ± 0.03
12.6
14.0
0.06± 0.02
17
29
0
D
A
8.41
7.5
194
6/12
4/12
14.7
0.08 ± 0.02
Popcorn to harvest
D
7.00
8.1
313'
6/21
4/9
13.4
2.77 ± 0.24
Popcorn to harvest
4
C
6.42
7.4
260
10.5
6/21
4/9
12.2
3.01 ± 0.18
C
7.91
13.6
268
7.29
2.6
364'
6/21
4/9
13.8
B
C
6.94
6.7
Weight Chlorosis
rating '
(g)
261'
Fruit set
(%)
244'
Firmness
(g)
7.92
6/21
4/7
15.4
0.90 ± 0.08
Popcorn to harvest
2
0.73 ± 0.08
6/21
4/9
12.4
26
31
34
3
6/21
4/9
15.0
0.14 ± 0.03
started
(%)
(µg F/m')
0.42 ± 0.04
tion
stopped
tion
solids
concn.
25
5
Fumiga-
Fumiga-
Soluble
Actual F
21
Cage
no.
Popcorn to harvest
duration
Treatment
1
Desired
F concn.
(µg F/m')
Oregon, 1966)-(Continued)
Table 11. Treatment duration, fluoride concentrations, and fruit data from `Napoleon' sweet cherry fumigation experiment (Mosier,
Table 13. Effect of hydrogen fluoride on `Napoleon' cherry pollen germination
(Mosier, Oregon, 1968 and 1969)
Daily average F
(µg F/m')
Treatment
Check
Budburst to harvest.......
Budburst to shuck.........
Budburst to shuck.........
Popcorntoshuck..........
Popcorn to shuck..........
Days fumigated
before pollen picked
1968
1969
1968
0
0
3.5
3.1
4.0
20.6
3.9
3.5
20.1
3.8
18.6
13
13
12
12
13
12
6
5
6
5
18.7
1969
Pollen
germination (%)
1969
1968
60.1a'
62.3 a
58.8 a
56.6 ab
53.5 ab
48.0 b
65.8 a
53.8 abc
49.9 be
33.5 d
63.0 ab
40.8 cd
' Means followed by the same letter are not significantly different from one another at the 5% level.
Table 14. Seasonal fluoride content of hydrogen fluoride fumigated
`Napoleon' cherry leaves (Mosier, Oregon, 1968)
Date
4/23
Treatment'
6/24
7/22
8/20
9/23
Fluoride content (ppm F)
Check ...................................
Check, outside cage ...................
Budburst to harvest,
Popcorn to shuck, 4
5/22
4 µg F/m'
µg F/m'........
6.7
12.6
13.6
4.1
15.2
7.8
152.1
8.0
4.0
184.8
30.3
127.1
65.9
41.2
Budburst to shuck, 20 µg F/m' 311.0
Budburst to shuck, 4 µg F/m' 94.3
Popcorn to shuck, 20 µg F/m' 173.3
16.9
239.4
82.8
70.8
310.5
23.6
254.4
76.6
85.9
79.3
42.7
9.7
4.0
130.9
38.1
75.8
57.4
70.0
8.1
....
115.1
29.5
30.6
63.6
71.2
' Averages of six replications: Budburst to harvest fumigated 82 days; popcorn to shuck, 10 days;
budburst to shuck, 32 days. Budburst was approximately March 24; popcorn was approximately
April 3.
Fluoride fumigation experiments, 1969
Results from the 1969 fumigation experiments are presented in Tables 13 and
15 and in Figure 4. Table 15 shows the treatments, fumigation duration, concentration, percent fruit set, and fruit firmness. As in 1968, there was no fruit in the cages
receiving air F levels greater than 18 µg F/m' for either 11 or 23 days during the
bloom period. Fruit set was reduced in the cages receiving greater than 3 to 4µg
F/m' as compared to caged controls. Fruit set was light in all instances with the
control limbs averaging only 10.9 percent fruit set. Fruit firmness at the stylar end
was greater in fruit fumigated with approximately 3µg F/m' only in the treatment
going to harvest. Fruit in this treatment was significantly smaller (Fig. 4) only at
harvest, the growth curves being comparable up to the last 2 weeks before harvest.
Pollen that had been fumigated with F at levels of 18 to 20 µg F/m' for 5 and/or 12
days had less germination percentage than nonfumigated pollen (Table 13). Results
were variable with the lower concentration cages but, in general, pollen germination was lower in fumigated pollen than in nonfumigated pollen.
-Check
0.9
4 ug F, Budburst to Harvest
&--a4ug F, Popcorn to Shuck
0.8
s- 4 ug F, Budburst to Shuck
0.7
0.6
0.5
0.2
0.1
0.0
20
25
30
35
40
45
50
55
60
65
Days From Full Bloom
Figure 4.
Effect of hydrogen fluoride fumigation on seasonal growth of `Napoleon' sweet
cherries.
Table 15. Effect of hydrogen fluoride fumigations on percent fruit set, weight, and firmness
of `Napoleon' sweet cherries (Mosier, Oregon, 1969)
Days
Treatment
fumigated
Check ...........................................
Budburst to harvest, 4 µg F/m' .............
Budburst to shuck, 4 µg F/m' ...............
Budburst to shuck, 20µg F/m' .............
Popcorn to shuck, 4 µg F/m2 ................
....
Popcorntoshuck,20µgF/m2 ...............
11
64
23
23
11
Daily avg.
(µg F/m2)
Fruit set
0.05
3.12
3.52
20.08
3.84
18.56
10.9 a'
8.3 b
2.8 c
(%)
02
3.1 c
02
Firmness
(g)
195 b
410 a
212 b
NF
178 b
NF
Means followed by the same letter are not statistically different at the 5% level.
In the statistical analysis performed, these treatments were not included as there was no fruit
present.
2
Fluoride fumigation experiments, 1970-1972
Fumigation with HF during anthesis resulted in a small but significant
reduction in fruit set of `Napoleon' cherries all 3 years (Figures 5 and 6).
Fumigation with HF when the fruit was in shuck had no effect on fruit set in 1970 or
Adjusted fumigated %fruit set=
15 5 -0.0184 dose HF
30}
N
373
r=-0.2169*
25}
t..
5}
25
50
75
100
125
150
175
200
I
1
225
250 -
DOSE HF (hr jig F/m3)
Figure 5.
Relationship between adjusted fumigated percent fruit set and dose of hydrogen
fluoride of `Napoleon' sweet cherry treated for 2, 4, and 6 hours at fluoride concentrations
ranging from 0.3 to 67.8µg F/m3. Data points are for years 1970 and 1971 and were adjusted
for variation in untreated limb percent fruit set, day fumigation done, year, and distance to
pollenizer (based on formula in Table 17). Dashed lines show the 95 percent confidence
interval for the data.
Table 16. Analysis of variance of percent fruit set on hydrogen fluoride fumigated
`Napoleon' sweet cherry limbs (Mosier, Oregon, 1970-1972)
1970-71
Source of variation
df
Dose of HF' ....................................
Check set ........................................
1972
M.S.
370.99***'
6122.37***
Distance to pollenizer ........................
M.S.
1
14.49*
1
10.41
1
32.97**
177.36*
Fumigated limb height
Days .............................................
Error ............................................
df
19
350
67.15**
28.60
All sources of variation are adjusted for the effects of remaining sources.
' Significant at 5% (*), 1% (**), and 0.1% (***) probability level.
27
2.46
7.0
Adjusted fumigated % fruit set
429- 0.0174 dose HF
N= 31
60
r = - 0.4347
50
4.0
-3.0
20
1.0
20
40
60
80
100
120
140
160
DOSE HF (hr jig F/m3)
Relationship between adjusted fumigated percent fruit set and dose of hydrogen
fluoride of `Napoleon' sweet cherry treated for duration of 21.5 to 26.7 hours and fluoride
concentrations ranging from 0.8 to 6.3 µg F/m'. Data are from 1972 and fruit set values
were adjusted for variation in untreated limb percent fruit set and fumigated limb height
above ground (based on formula in Table 18). Dashed lines show the 95 percent confidence
interval for the data.
Figure 6.
1971. No visible injury occurred on any treated limb. Several factors other than
fumigation had significant effects upon the fruit set of fumigated limbs in 1970 and
1971 (Table 16). The general level of fruit set on the tree (Ck) was by far the most
significant factor. However, the distance to the nearest pollenizer (DP) and years
(Y) and days within years had significant effects, in addition to the effects of the
dose (D) of HE The following multiple regression model, which includes constants
for years and days within years, accounts for 55.4 percent of the variation in fruit
set on fumigated limbs:
Percent fruit set on fumigated limbs = 8.25 - .0184D - .571Ck - .818DP
The constants estimating the effects of days ranged from - 4.6 to + 6.3 (see Table
17 for the full model). To observe the effects of fumigation, an adjusted fruit set
was computed. The effect of the general level of fruit set (Ck) was removed by
subtracting the quantity .571 (Ck - 15.2) from each observed fumigated set. The
mean set of all unfumigated limbs was 15.2. The result is that all observations
appear as if they were from trees with the same general level of fruit set (15.2). The
effects of DP and days were similarly removed. This simplifies the equation to:
Table 17. Model for the effects of untreated fruit set, distance to pollenizer, dose of
hydrogen fluoride,' year fumigation done, and day fumigation done on fumigated percent
fruit set of `Napoleon' sweet cherry (1970 and 1971)
Fumigated percent fruit set = 8.2543E + 00
-8.1813E-01 Distance to pollenizer
-1.6586E-01 Year
+ 5.7076E-01 Untreated percent fruit set
-1.8432E-02 Dose
-2.3594E+00 Day 701
+ 2.9003E + 00 Day 702
+ 3.2478E-01 Day 704
+ 3.5230E + 00 Day 703
-2.0438E + 00 Day 706
+ 7.3422E-02 Day 705
+ 1.6293E-01 Day 708
-6.6305E-01 Day 707
-7.6409E-01 Day 709
-4.3980E + 00 Day 711
+ 6.4455E + 00 Day 712
+ 1.5367E+00 Day 713
-1.4389E-01 Day 715
-6.4290E-01 Day 717
-2.6552E + 00 Day 719
N = 373, r2 = 0.5542
+ 1.6910E + OO Day 714
Variable
Untreated percent fruit set .......................
+ 1. 1714E + 00 Day 716
-1.2466E+00 Day 718
T values2
14.63***
Distance to pollenizer ............................
Variable
Day 708
T values
0.13
Day 709
-0.62
-2.49*
Dose HF ................................-3.60**
Year .....................................
-0.48
Day 701' ................................ -1.59
Day 711
Day 712
Day 713
Day 702 .................................
Day 714
1.20
Day 715
-0.14
Day 703 .................................
Day 704 .................................
2.30*
3.04**
0.28
Day 705 ................................. -0.04
Day 706 ................................. -1.23
Day 707 ................................. -0.54
-1.78
3.68**
1.55
Day 716
1.17
Day 717
Day 718
Day 719
-0.64
-1.22
-2.20
Concentration HF in µg F/m' x duration of fumigation in hours.
Significance levels:*** = 0.1%; ** = I%; * = 5076.
' Code is 70, 71 for year, 1-9 for day of fumigation.
fumigated fruit =15.5 - 0.0184D. Figure 5 was then prepared to show the effect of
fumigation with HF. The 95 percent confidence limits shown on Figure 5 reflect the
expectations of the effect of HF on fruit set for a large number of trees rather than
for single samples of 300 to 400 flowers which are plotted.
The frost in 1972 presented the potential for substantial differences from the
results found in 1970-1971. The average fruit set of 31 check limbs was only 4.7
percent in contrast to the 15.2 percent in the previous years. Even so, both are well
below the values considered by Westwood and Stevens (1979) for a full crop of fruit
(30 to 60% fruit set). The effect of the general level of fruit set (Ck) was not nearly as
important as a source of variation when set was reduced to this level (Table 16).
Distance to the pollenizer and days were not statistically significant. Because of the
frost, the height of the check and treated limbs above the ground was measured,
and height (Ht) of the fumigated limb was a significant source of variation. The
following multiple regression model accounted for 51.1 percent of the variation in
fruit set on fumigated limbs (see Table 18 for full model and F values):
Percent fruit set on fumigated limbs = 1.95 - 0.0174D + .239Ck + 0.028Ht
The notable fact is that the slopes of the dose response were so remarkably similar
(1970-1971 slope = - 0.0184 and 1972 slope = - 0.0174).
The 1972 experiment included fumigation for longer periods at generally lower
concentrations of HF, but the effect of increasing dose was a decrease in fruit set
almost identical to that found in 1970-1971. In neither 1970-1971 nor 1972, were we
able to identify evidence of a threshold concentration or a quadratic response. The
variability found, especially in 1970-1971 (Fig. 5), makes it difficult to identify such
a response. Simple plots of fruit set and dose for separate days suggested some
inconsistency of response. These plots could not practically take into account such
factors as the general level of fruit set, distance to the pollenizer, and limb height.
However, an extensive effort was made to consider the reality of the day-to-day
inconsistency by looking for evidence of interaction between days and dose. We
found no statistical evidence of such interactions.
No untreated limbs were caged in 1970-1971, but specific effects of caging were
examined in 1972. Caging did not appear to have an effect on fruit set for durations
of 2, 4, 6, or 24 hours (Table 19). There also was no real difference between the fruit
set on caged limbs and uncaged limbs on the same tree. The actual average fruit set
was 6.0 percent on the caged limbs and 4.4 percent on the uncaged limbs. However,
the average heights of the limbs were substantially different (caged = 185 cm;
Table 18. Model for effects of untreated fruit set, fumigated limb height, and dose of
hydrogen fluoride' on fumigated percent fruit set of `Napoleon' sweet cherry (1972)
Fumigated percent fruit set = -1.95 + 0.0279 fumigated limb height
+ 0.2393 untreated percent fruit set -0.0174 dose HF
N=31,r'=0.5109
Variable
Fumigated limb height (cm) .....................
Untreated fruit set (%) ...........................
Dose (hr µg F/m') .................................
Time .................................................
Concentration .....................................
T values'
3.66**
2.06*
-2.43*
1.60
-0.78
Frost (% flowers damaged) ......................
0.11
Concentration HF in µg F/m' x duration of fumigation in hours.
' Significance levels: ** = 1%; * = 5%.
Table 19. Analysis of variance of percent fruit set on caged, untreated `Napoleon' sweet
cherry limbs with limb height as a covariant (The Dalles, Oregon, 1972)
Source of variation
df
M.S.
Trees .................................................................
60
18.52**
Caging ..............................................................
Limb height ........................................................
Error ................................................................
'
1
1
59
0.45
58.47**
7.13
Significant at the 1% (**) probability level.
27
uncaged = 234 cm), and such a difference in height would be expected to have the
observed effect because of the frost conditions that occurred. An analysis of
covariance (Table 19) using limb height as the covariate showed no real effect of
caging. The mean percent fruit sets (adjusted to a common height = 209.6 cm) were
5.1 for the caged limbs and 5.3 for the uncaged limbs, which is not significantly
different. It is useful to compare these results with the 1972 model for the effects of
fumigation at the limb height (210 cm) and average fruit set (5.2 %) of the untreated
caged and uncaged limbs. This simplifies the regression equation to fumigated fruit
set = 5.16 - 0.174D. The estimated fruit set (5.16) at 0 dose is not different from
the average fruit set of the caged, untreated limbs and their uncaged counterparts.
Increasing dose of HF resulted in a decrease in the difference between the 3-day
pollen tube lengths and the 0-day values (Fig. 7). Flowers were sampled at the time
30
A PTL = 24.7- 0.161 dose HF
N= 28
25
r= -0.7389'
Ic
20
10
5
20
40
60
100
120
140
160
DOSE HF (hr jig F/0)
Figure 7.
Relationship between the difference in pollen tube lengths of samples taken
initially (0 day) and 72 hours after pollination and fumigation (3 day) and hydrogen fluoride
dose of `Napoleon' sweet cherry, 1972.
of fumigation to make sure that no insect-transferred pollen or windblown pollen
had started growth before fumigation. Since some growth was evident at 0 days, the
difference in the two fruit sets observed was used as a measure of the effect of dose
on pollen tube growth and of pollen tube growth on adjusted fruit set. The
predicted difference in pollen tube growth between the 3-day and 0-day values
without fumigation was 24.7 (Fig. 7), which was within the 95 percent confidence
interval for the ambient caged pollen tube difference (32.9 ± 9.0%). The difference
between the 3-day and 0-day pollen tube lengths was also positively correlated to
adjusted fumigated fruit set (Fig. 8).
7.0
Adjusted fumigated % fruit set
2.12 + 0.068 A PTL
6.0
N= 28
r=0.3823
.0
4.0
3.0
1.0
0t
25
5
10
15
20
A POLLEN TUBE LENGTH (3day-Oday)
30
Figure 8. Relationship between adjusted hydrogen fluoride fumigated percent fruit set of
`Napoleon' cherry (see text for explanation) and the difference in pollen tube lengths of
samples taken initially (0 day) and 72 hours after pollination (3 day). Pollen tube lengths were
based on percent style length of longest pollen tube visible.
Fluoride fumigation experiments, 1975-1978
Gaseous HF fumigations of 1.5 and 6.1 µg F/m' in 1975 and 1.5 µg F/m' in
1976 reduced central leader terminal growth of newly budded, nonbearing 'Napoleon' trees when trees were treated through the entire growing season each year
(Table 20). Trees fumigated during two growing seasons, 1975 and 1976 (called
1-year trees), had reduced average total terminal growth in 1976 at the highest level
treatment. Fumigations in 1977 and 1978 were at lower air F levels, and although
not statistically significant, both years' data indicate that increasing gaseous F
might reduce terminal growth (Table 20). The high F concentration in 1975 caused a
significant reduction in growth of the central leader, but the high F promoted more
side branching (0.6, 0.6, and 1.13 shoots per tree at 0.08, 1.5, and 6.1 µg F/m',
respectively), resulting in no statistical differences in average total terminal growth.
Limb diameter was significantly reduced at the highest concentration (1.20, 0.96,
and 0.83 cm at 0.08, 1.5, and 6.1µg F/m', respectively). This response was not seen
other years when air F concentrations were lower than 6.1 µg F/m'. Leaf symptoms
of F toxicity were found on all treatments when the leaf F levels were greater than 30
ppm F and consisted of: (1) interveinal chlorosis on all leaves, (2) tip burn on leaves
where the F levels were greater than 100 ppm F, and (3) marginal necrosis, cupping,
and defoliation where the levels were greater than 265 ppm F. Increasing leaf F
levels were related to increasing air F concentrations.
Table 20. Growth response of nonbearing `Napoleon' sweet cherry to hydrogen fluoride
gas fumigation
Avg. terminal
Air F
concn.
(µg F/m')
Date
No.
growth,
central
started'
trees
leader (cm)
Avg. total
growth, all
Sept. leaf F
terminal (cm) (ppm dry wt.)
1975, newly budded trees
0.08
1.50
6.10
5/16/75
0.02
3/26/76
15
101.3 a2
14
85.9 b
67.6 c
15
117.4 a
102.6 a
98.1 a
6.6
265.0
1070.0
1976, newly budded trees'
15
92.3 a
92.3 a
5.7
0.26
15
1.50
14
88.0 a
69.7 b
88.0 a
69.7 b
111.4
593.9
1976, 1-year trees
0.02
5/6/75
13
40.9 a
134.7 a
0.26
14
32.5a
110.3a
111.4
1.50
14
36.7 a
100.0 b
593.9
5.7
1977, 2 -year trees
0.01
3/28/77
0.24
0.80
9
26.5 a
148.7 a
4.6
9
25.5 a
20.0 a
136.8 a
118.8 a
26.6
78.7
121.9 a
100.6 a
2.2
29.0
7
1978, newly budded trees'
0.02
0.16
2/27/78
8
13
121.9 a
100.6 a
Newly budded trees fumigated from first sign of budswelling. One-year trees were started in 1976
and fumigated constantly. Two-year trees had not been fumigated and were started before budswell in
1977. All newly budded trees were budded the previous August on Mazzard rootstock.
2 Means separation by LSD, 5 % level.
' No side shoots developed; therefore, terminal growth (both central leaders and all terminals) was
the same.
DISCUSSION
Fruit set
Sprays containing F and application of gaseous F both reduced fruit set of
sweet cherries. The most susceptible period appeared to be during bloom, as
treatment with F during other stages of growth had no effect on fruiting. The
concentration where F will reduce fruit set was not definable. Treatment to
individual limbs, where more replicates were used, showed that spray levels of 25
ppm F (1963) and 50 ppm (1961, 1974-1978) reduced fruit set. Other treatments, as
high as 500 ppm F applied during bloom (1961, 1962), had no significant effect on
fruit set even though yields and fruit size were restricted. There was only one spray
of 500 ppm F during bloom in 1961, and all flowers probably were not in a
susceptible stage since stage of bloom varies on individual limbs. Treatment to
emasculated flowers (1961) or multiple sprays of either 10 ppm (1963) or approximately 50 ppm (1971-1978) caused significant fruit set reductions at lower F
concentrations, generally where more replicates were used.
Fumigation experiments conducted from 1966-1972 showed that gaseous F
reduced fruit set. These experiments offer a more direct comparison of the effects
of F because most ambient F is in the gaseous form instead of a spray. Plant
response to F was extremely variable (Fig. 5), and it was not surprising that the
1966-1967 fumigation experiments, where only three and nine limbs were tested at
each timing, showed no decreases in fruit set. Reasons for the variability are
unknown but probably were related to nutrition, environment, variation in bloom,
variation in pollination, possible genetic variation between trees, and other
unknown factors. The data indicate that reduction of fruit set by gaseous F could be
best expressed as linear with respect to increasing F dose. However, variability in
data makes it difficult to determine the exact nature of the response. High
concentrations of pollutants for short periods of time should have more effect on
plants than low concentrations for longer periods (Webster, 1967). Pollen tube
growth of sweet cherry in response to F does not follow this pattern (Facteau et al.,
1973), although apricot pollen tube growth does (Facteau and Rowe, 1977). Work
is being done to clarify the potentially separate effects of exposure time and F
concentration on sweet cherry fruit set. Lai Dinh et al. (1973) reported that cherry
fruit set was not influenced by 2.5 µg F/m' near a hydrofluoric acid factory,
although they compared only hand and natural pollination, not fumigated and
nonfumigated flowers. MacLean et al. (unpub. data cited in Weinstein, 1977)
"found that reduced pollination in sweet cherry required a high dose of F." It is not
clear what was meant by pollination, per se. Facteau and Mellenthin (1976)
reported on a correlative field study that they believed suggested that increasing
fruit set of `Napoleon' sweet cherries was related to increasing distance from an
aluminum plant and also related to direction from the factory. This bulletin
describes some of the experimental data supporting that conclusion.
One should be cautious of directly using data collected in fumigation chambers
in assessing damage in field situations. Work with SO2 has shown that plants tend to
have higher threshold values for injury when treated under controlled exposure
conditions as compared to ambient conditions (Jones et al., 1974). Differences in
plant response to ozone between field-grown plants and those from growth
chambers have been noted, but results were comparable between open-top cham-
bers and field-grown plots (Lewis and Brennan, 1977). Manning and Feder (1976)
and Larsen and Heck (1976) also questioned the use of fumigation chambers in
assessing plant damage by pollutants.
Pollen germination and pollen tube growth
Germination of sweet cherry pollen was reduced by levels greater than 2.5 ppm
Fin an artificial media. Germination also was reduced when pollen was exposed to
gaseous F at fairly high F concentrations (approximately 4 and 20µg F/m') for long
periods of time (1968 and 1969). Increasing dose of F decreased pollen tube growth,
in vivo, in the field caging experiments in 1972. Facteau et al. (1973) reported that
increasing F dose resulted in decreased pollen tube growth in flowers forced from
cut branches and treated under more controlled conditions than those of the field
experiment reported in this bulletin. Lai Dinh et al. (1973), however, concluded that
sweet cherry pollen grains were very resistant to F gases and that fertilization and
fruit set would be influenced only when blossoms were damaged. They reported
that 97 µ F/m' reduced pollen germination after a 24-hour exposure, and a 48-hour
exposure reduced both germination and tube growth. Fluoride effects on tomato
and cucumber pollen germination, pollen tube growth, and fruit development led
Sulzbach and Pack (1972) to indicate that F probably would interfere with fruit set
although the F treatments that resulted in the responses were high in comparison to
levels of F generally reported in the ambient air. In another study, Pack and
Sulzbach (1976) reported that, in the plant species they studied, the HF effect on
fruiting probably was independent of foliage symptoms, but depended on the
presence of F in a critical concentration at a critical point of growth. Fruiting of
some species was affected at HF concentrations commonly considered for air F
quality standards. Leonard and Graves (1966) stated that exposure of citrus trees to
F during spring bloom caused the greatest losses in fruit production, although they
did not know the mechanism by which the losses occurred.
Since pollen tube growth is an essential part in the process of setting sweet
cherry fruit, a reduction or inhibition in pollen germination and/or pollen tube
growth could interfere with fruit set. Eaton (1959) reported that degeneration of the
egg of `Windsor' sweet cherry occurs shortly after anthesis and delaying pollination
1 to 2 days after anthesis reduces fruit set.
Fluoride symptoms
Symptoms of F toxicity were found in both the F spray and fumigation
experiments only at the longer fumigation times or the higher F spray levels. For
instance, no leaf or fruit symptoms were found in the short-term fumigations
(1971-1972) nor in the long-term, low-level (less than 50 ppm F) spray experiments
in 1973-1978. Foliar symptoms were similar to those described for other plant
species (Treshow and Pack, 1970) and consisted of interveinal chlorosis and some
necrosis in severe cases. Fruit symptoms were similar to those described by Treshow
and Pack (1970), Lai Dinh et al. (1973), and Bolay and Bovay (1965) for cherries
and apricots. These symptoms have been seen in The Dalles area directly after an
aluminum reduction plant began operation, but, except for some fruit shrivel
symptoms in 1970, have not been seen for at least 10 years (Mid-Columbia
Experiment Station, unpub. data). Lack of symptom expression does not imply no
other response. Fruit set was reduced in the fumigation experiments of 1970-1972
and in the spray experiments in 1973-1978. Pack and Sulzbach (1976) also reported
that some plant species might have symptoms and no effects on fruiting or
vice versa.
Growth
Vegetative growth was reduced where the air F concentrations were very high
(greater than 1.5 µg F/m') for the entire growing season. Growth tended to be
decreased by F at levels much lower than 1.5 µg F/m' (approximately 0.2µg F/m'),
but the results were not statistically significant.
Fumigation response reported here indicates that gaseous F may reduce sweet
cherry growth, as suggested in a field survey where reduced growth was associated
with increasing leaf F levels, distance, and direction from an aluminum reduction
factory (Facteau and Mellenthin, 1976). However, these fumigation results were on
nonbearing trees in fumigation chambers and may not be indicative of responses
found under varying ambient conditions. None of the other fumigation experiments gave any indications that sweet cherry vegetative growth would be affected
by F. The F-spray treatments during 1973-1979 showed that limbs measured on
F-sprayed trees had more terminal growth and generally more flower buds,
flowering spurs, total spurs, and flowers.
The increased growth in the F-sprayed trees could be a result of reduced fruit
set since increased cropping may reduce shoot growth (Chandler, 1951). Fumiga-
tions of nonbearing trees tended to reduce growth, further suggesting that the
response in the F-sprayed trees was not a direct effect of F. When F is applied in an
aqueous spray, a greater amount may be necessary to cause a reduction in growth
than when gaseous F is used. Continuous exposure to gaseous HF caused more
growth retardation in oranges than did aqueous F, even though leaf F levels were
similar (Brewer et al., 1969a).
Fruit growth was reduced only by the higher concentration sprays (1961, 1962)
or by lower concentration sprays (1963) applied throughout the fruit-growing
season. Only the long-term, high-level F fumigation treatments of 1969 reduced
fruit size. It seems likely that high levels of F directly reduce fruit size. Lower F
concentrations may indirectly increase size by reducing fruit set.
Fruit firmness
Fruit firmness on the stylar end was enhanced by high concentration F sprays
during bloom (1961), lower concentrations closer to harvest but not during bloom
(1963), or application throughout the growing season (1975-1976). Similarly,
fumigations with gaseous F increased firmness only when applied for the growing
season but not during bloom (1966, 1967, 1969).
33
LITERATURE CITED
Bolay, A., and E. Bovay. 1976. Observations sur les degats provoques par les corn poser
fluorides envalais. Agriculture Romande, 4A:43-46.
Brewer, R. F., R. K. Creveling, F. G. Guillemet, and F. H. Sutherland. 1960a. The effects of
hydrogen fluoride gas on seven citrus varieties. Proc., Amer. Soc. Hort. Sci., 75:236-243.
Brewer, R. F., F. H. Sutherland, F. B. Guillemet, and R. R. Creveling. 1960b. Some effects
of hydrogen fluoride gas on bearing navel orange trees. Proc., Amer. Soc. Hort. Sci.,
76:208-214.
Brewer, R. F., M. J. Garber, F. B. Guillemet, and F. H. Sutherland. 1967a. The effects of
accumulated fluoride on yields and fruit quality of `Washington' navel oranges. Proc.,
Amer. Soc. Hort. Sci., 91:150-156.
Brewer, R. F., F. H. Sutherland, and F. B. Guillemet. 1967b. The relative susceptibility of
some popular varieties of roses to fluoride air pollution. Proc., Amer. Soc. Hort. Sci.,
91:771-776.
Brewer, R. F., F. H. Sutherland, and F. B. Guillemet. 1969a. Effects of various fluoride
sources on citrus growth and fruit production. Environ. Sci. Technol., 3:378-381.
Brewer, R. F., F. H. Sutherland, and R. O. Perez. 1969b. The effects of simulated rain and
dew on fluoride accumulation by citrus foliage. Jour. Amer. Soc. Hort. Sci., 94:284-286.
Chandler, W. H. 1951. Deciduous Orchards. Lea and Febiger, Philadelphia.
Cralley, L. V., L. V. Haff, A. W. Hook, E. J. Schneider, J. F. Strauther, C. R. Thompson,
and L. H. Weinstein. 1969. Tentative method of analysis for fluoride content of the
atmosphere and plant tissues (semiautomated method). Health Laboratory Sci.,
6:84-101.
De Ong, E. R. 1946. Injury to apricot leaves from fluorine deposits. Phytopathology,
36:469-471.
Eaton, G. W. 1959. A study of the megagametophyte in Prunus avium and its relation to
fruit setting. Can. Jour. Plant Sci., 39: 466-476.
Facteau, T. J., S. Y. Wang, and K. E. Rowe. 1973. The effect of hydrogen fluoride on pollen
germination and pollen tube growth in Prunus avium L. cv. `Royal Ann.' Jour. Amer.
Soc. Hort. Sci., 98:234-236.
Facteau, T. J., and W. M. Mellenthin. 1976. Fluoride investigations in The Dalles area
1968-1974. Oregon Agric. Expt. Sta. Tech. Bull. 132.
Facteau, T. J., and K. E. Rowe. 1977. Effect of hydrogen fluoride and hydrogen chloride on
pollen tube growth and sodium fluoride on pollen germination in 'Tilton' apricot. Jour.
Amer. Soc. Hort. Sci., 102:95-96.
Hill, A. C., L. G. Transtrum, M. R. Pack, and A. Holloman Jr. 1959. Facilities and
techniques for maintaining a controlled fluoride environment in vegetation studies.
Jour. Air Pollut. Control Assoc., 9:22-27.
Hitchcock, A. E., P. W. Zimmerman, and R. R. Coe. 1963. The effects of fluorides on Milo
maize (Sorghum sp.). Contrib. Boyce Thompson Inst., 22:175-206.
Hitchcock, A. E., L. H. Weinstein, D. C. McCune, and J. S. Jacobson. 1964. Effects of
fluorine compounds on vegetation, with special reference to sweet corn. Jour. Air
Pollut. Control Assoc., 14:503-508.
Hitchcock, A. E., D. C. McCune, and L. H. Weinstein. 1971. Effects of hydrogen fluoride
fumigation on alfalfa and orchard grass: A summary of experiments from 1952 through
1965. Contrib. Boyce Thompson Inst., 24:363-386.
Jones, H. D., D. Weber, and D. Basille. 1974. Acceptable limits for air pollution dosages and
vegetation effects: sulfur dioxide. Paper No. 74-225, 67th Ann. Meeting of the Air
Pollut. Control Assoc., Denver, Colorado.
Lai Dinh, D., G. Buchloh, and W. Oelschlager. 1973. Auswirburg von fluoverbindungen auf
die pollenbeimung and den fruchtonsetz von obstgewachsen. Der Erwerbsobstbau,
15:154-157.
Larsen, R. I., and W. W. Heck. 1976. An air quality data analysis system for interrelating
effects, standards, and needed source reductions. Part 3, Vegetation injury. Jour. Air
Pollut. Control Assoc., 26:325-328.
Leonard, C. D., and H. B. Graves, Jr. 1966. Effect of airborne fluorides on `Valencia'
orange yields. Proc., Florida State Hort. Soc., 79:81-86.
Lewis, E., and E. Brennan. 1977. A disparity in the ozone response of bean plants grown in a
greenhouse, growth chamber, or open-top chambers. Jour. Air Pollut. Control Assoc.,
27:889-891.
Mandl, R. H., L. H. Weinstein, G. J. Weiskopf, and Judy L. Major. 1971. Separation and
collection of gaseous and particulate fluorides. 2nd Int. Clean Air Congr. Paper
CP25A:450-458.
Manning, W. J., and W. Feder. 1976. Effects of ozone on economic plants. In Effects ofAir
Pollutants on Plants, edited by T. A. Mansfield. Cambridge University Press, Cambridge.
Mellenthin, W. M., and D. Bonney. 1972. A portable limb enclosure for temperature
modification of tree fruits. HortScience, 7:134-136.
Pack, M. R., and C. W. Sulzbach. 1976. Response of plant fruiting to hydrogen fluoride
fumigation. Atmospheric Environment, 10:73-81.
Schuster, C. E. 1925. Pollination and growing of the cherry. Oregon Agric. College Expt.
Sta. Bull. 212.
Sulzbach, C. W., and M. R. Pack. 1972. Effects of fluoride on pollen germination, pollen
tube growth, and fruit development in tomato and cucumber. Phytopathology,
62:1247-1253.
Thompson, C. R., and J. O. Ivie. 1965. Methods for reducing ozone and/or introducing
controlled levels of hydrogen fluoride into airstreams. Int. Jour. Air Water Pollut.,
9:799-805.
Treshow, M. F., F. K. Anderson, and F. Harrier. 1967. Response of Douglas-fir to elevated
atmospheric fluorides. Forest Sci., 13:114-120.
Treshow, M. F., and F. M. Harrier. 1968. Growth responses of pinto bean and alfalfa to
sublethal fluoride concentrations. Can. Jour. of Botany, 46:1207-1210.
Treshow, M. F., and M. R. Pack. 1970. Fluoride. In Recognition of Air Pollution Injury to
Vegetation, edited by J. S. Jacobson and A. C. Hill, pp. D1-D17. Air Pollution Control
Association, Pittsburgh.
Webster, C. C. 1967. The effects of air pollution on plants and soil. Agriculture Research
Council, London.
Weinstein, L. H. 1977. Fluoride and plant life. Jour. Occupational Medicine, 19:49-78.
Weinstein, L. H., R. H. Mandl, D. C. McCune, J. S. Jacobson, and A. E. Hitchcock. 1963.
A semi-automated method for the determination of fluorine in air and plant tissues.
Contrib. Boyce Thompson Inst., 22:207-220.
Westwood, M. N., and G. Stevens. 1979. Factors influencing cherry and prune set. Proc.,
Ore. Hort. Soc., 70:175-179.
35