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This is to certify that the
thesis entitled

DEICING SALT INJURY TO HIGHBUSH BLUEBERRY
(Vaccinium corymbosum L.) IN WEST MICHIGAN

presented by

STEVEN F. BERKHEIMER

has been accepted towards fulﬁllment
of the requirements for the

MS. degree in HORTICULTURE

 

 

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DEICING SALT INJURY T0 HIGHBUSH BLUEBERRY (Vaccinium corymbosum
L.) IN WEST MICHIGAN

By

Steven F. Berkheimer

A THESIS

Submitted to
Michigan State University
in partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Horticulture

2004

ABSTRACT
DEICING SALT INJURY TO HIGHBUSH BLUEBERRY (Vaccinium corymbosum L.)
IN WEST MICHIGAN.
By

Steven F. Berkheimer

Varying rates of ﬂower bud mortality on blueberries growing adjacent to roads in
West Michigan have been observed since the early to mid-19903; the purpose of these
studies was to investigate the inﬂuence of deicing salt (primarily sodium chloride, NaCl)
to this injury. Injury was surveyed in the spring on 12 farms by recording ﬂower bud
mortality at numerous locations, and mapped graphically with GPS technology. The
most severe injury occurred closest to heavily traveled roads. Potted plants sprayed with
NaCl or receiving soil applications exhibited similar symptoms observed on roadside
plants, with injury severity proportional to the NaCl concentration. Salts rinsed from
twigs sampled prior to each successive spray were in the same range as salts rinsed from
twigs sampled from ﬁeld-grown plants in the winter months. The highest soil salt levels
killed most above ground growth, suggesting that injury in the ﬁeld results primarily
from salt deposition on buds and twigs.

Twigs were also excised from salt treated and control branches and frozen
incrementally to measure LTso. Salt exposure (e.g., chloride salts [NaCl, KCl, CaClz,
MgClz] and sodium salts [NaCl, NaAC]) reduced the LTso of ﬂower buds by as much as

11.0 °C relative to the control, even within 7 hours of treatment.

DEDICATION

This work is dedicated to the memory of Francis Tucker Berkheimer (1937 - I984) and

Michael Kickova (1913 — 1978). I miss you both very much.

iii

ACKNOWLEDGEMENTS

I would be remiss to not extend my most sincere thanks to my major professor
and supervisor, Dr. Eric Hanson: Thank you for your patience, professionalism, ethos,
and for believing in me.

No less sincere are my thanks to my guidance committee members, Drs; Stan
Howell, Bernie Knezek, Jim Hancock, and Bert Cregg for their critical input, intellectual
creativity, and willingness to serve in this capacity.

Thanks also to Mr. Chuck Pistis and Dr. Carlos Garcia-Salazar, MSU Extension,
Ottawa County, for assistance with this project. I would also like to acknowledge
ﬁnancial support from MBG Marketing, cooperating Ottawa and Muskegon County
Blueberry Growers, Ottawa County Road Commission and Board of County
Commissioners, and for advice and deicing materials from Michigan Department of
Transportation. The following individuals provided advice, assistance and friendship
during the course of this work: Pete Callow, Jon Dahl, Jen Dwyer, Thomas Heﬂ‘ran, Ms.
Kristi Lowrie, José Manuel Montecino-Piﬁa and family, Jason K. Potter, Dr. Paolo
Sabbatini, Audrey and Chris Sebolt, Dario Steffanelli, Dr. Daryl Wamcke, Dr. Phillip
Wharton, and Dr. Bernie Zandstra. Love and many thanks to my beloved sister
Cassandra.

Also acknowledged is the work of the previous students and Professors of this
department who studied this topic before me: Dr. William Bar-rick, Luther Moxley,
Professor Harold Davidson, and Professor Jim Flore. Sadly, Professor Davidson passed

away in August, 2002.

iv

Special thanks and recognition to Professor M. J. Bukovac for his critical review

of, and contribution to this work.

TABLE OF CONTENTS

LIST OF TABLES ................................................. vii
LIST OF FIGURES ................................................ viii
CHAPTER 1: REVIEW OF LITERATURE ........................ I
Charactersitics of Deicing Salts ....................................... 2
Toxicity of Deicing Compounds ....................................... 4
Chemical Preperties of Sodium Chloride ................................. 5
Salt Spray Injury to Plants ............................................ 6
Physiological Basis of Salt Injury to Plants ............................... 10
Woody Plant Cold Hardiness ......................................... l3
Supercooling ................................................... 16
Deep Spercooling ................................................... 16
Blueberry Cold Hardiness ............................................. 19

CHAPTER 2: FLOWER BUD MORTALITY AND NaCl LEVELS IN
BLUEBERRY FIELDS ADJACENT TO SALTED ROADS IN MICHIGAN

Abstract ......................................................... 37
Introduction ....................................................... 39
Materials and Methods ............................................... 42
Results ............................................................ 48
Discussion ......................................................... 69
Literattu'e Cited ....................................................... 74

CHAPTER 3: DEICIN G SALTS REDUCE COLD HARDINESS AND INCREASE
FLOWER BUD MORTALITY OF HIGHBUSH BLUEBERRY

Abstract ......................................................... 78
Introduction ................................................... 80
Materials and Methods .............................................. 82
Results ........................................................... 87
Discussion ....................................................... 93
Literature Cited ................................................... 101
CHAPTER 4: CONCLUSIONS ..................................... 105
APPENDICES .................................................... 110

vi

LIST OF TABLES

TABLE 1: Comparison of various deicing chemicals. Note: For general comparison
only; published values of lowest effective temperatures vary widely.
*BOD = Biochemical oxygen demand. .................................. 26

TABLE 2: Location, number of observations, and surface area of Michigan Blueberry
farms surveyed for ﬂower bud mortality in May. ............................ 47

TABLE 3: Results of May farm surveys, 2002 — 2004, showing mean and range of
ﬂower bud mortality. .................................................. 48

TABLE 4: Relationship between ﬂower bud mortality (y) and distance from road (in
meters) (x), on blueberry farms, by road type, 2002 -— 2004. ................ 50

TABLE 5: Soil Na+ and Cl' concentrations and new dry matter production (leaves,
shoots, fruit) by 20 June 2002 of potted ‘Bluecrop’ blueberry plants treated with NaCl
solutions applied to the rootzone on 1 Mar. 2002. ...................... 88

TABLE 6: Cold hardiness of ﬂower buds measured on 2 Jan., 03 treated with NaCl
sprays applied to branches of ‘Bluecrop’ highbush blueberry on 21 and 22 Dec. 02. . . 89

TABLE 7: Cold hardiness of ﬂower buds measured on 9 Mar., 03 treated with NaCl
sprays applied to branches of ‘Bluecrop’ highbush blueberry on 27 and 28 Feb. 03. . . 90

TABLE 8: Cold hardiness of ﬂower buds measured on 21 Jan., 04 treated with Cl' salt
solutions applied to branches of ‘Jersey’ highbush blueberry on 13 and 14 Jan. 2004.
................................................................ 91

TABLE 9: Cold hardiness of ﬂower buds measured on 23 Jan., 04 treated with selected

Na+-salts applied to branches of ‘Jersey’ highbush blueberry on 15 and 16 Jan. 2004.
................................................................ 9]

vii

LIST OF FIGURES

FIGURE 1: Map of Ottawa and Muskegon County farms surveyed for ﬂower bud
mortality, May 2002 - 2004. ........................................ 46

FIGURE 2: Relationship between ﬂower bud mortality (y) and distance from road (x) at
farms ‘A’, I’, ‘J’, and ‘L’, in 2002, 2003, and 2004. ...................... 51

FIGURE 3: Relationship between ﬂower bud mortality (y) and distance from road (x) at
farms ‘FG’, and ‘H’, in 2002, 2003, and 2004. ............................ 52

FIGURE 4: Relationship between ﬂower bud mortality (y) and distance ﬁ'om road (x) at
farm ‘K’, in 2002, 2003, and 2004. .................................. 53

FIGURE 5: Percent ﬂower bud mortality on farm ‘H’ in May 2002 illustrating ﬁeld
locations relative to the adjacent roads. .................................. 54

FIGURE 6: Percent ﬂower bud mortality on farm ‘H’ in May 2003 illustrating ﬁeld
locations relative to the adjacent roads. .................................. 55

FIGURE 7: Percent flower bud mortality on farm ‘H’ in May 2004 illustrating ﬁeld
locations relative to the adjacent roads. .................................. 56

FIGURE 8: Percent ﬂower bud mortality on farm ‘1’ in May 2002 illustrating ﬁeld
locations relative to the adjacent roads. .................................. 57

FIGURE 9: Percent ﬂower bud mortality on farm ‘1’ in May 2003 illustrating ﬁeld
locations relative to the adjacent roads. .................................. 58

FIGURE 10: Percent ﬂower bud mortality on farm ‘1’ in May 2004 illustrating ﬁeld
locations relative to the adjacent roads. .................................. 59

FIGURE 11: Percent ﬂower bud mortality on farm ‘K’ in May 2002 illustrating ﬁeld
locations relative to the adjacent road. .................................. 60

FIGURE 12: Percent ﬂower bud mortality on farm ‘K’ in May 2003 illustrating ﬁeld
locations relative to the adjacent road. .................................. 61

FIGURE 13: Percent ﬂower bud mortality on farm ‘K’ in May 2004 illustrating ﬁeld
locations relative to the adjacent road. .................................. 62

FIGURE 14: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at
farm ‘B’, Ottawa County, Mich., 2003. Bars represent standard error. Legend indicates
distance to road. .................................................... 65

viii

FIGURE 15: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at
farm ‘C’, Ottawa County, Mich., 2001 - 2003. Bars represent standard error. Legend
indicates distance to road. .............................................. 66

FIGURE 16: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at
farm ‘1’, Ottawa County, Mich., 2001 - 2003. Bars represent standard error. Legend
indicates distance to road. .............................................. 67

FIGURE 17: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at
farm ‘K’, Ottawa County, Mich, 2003. Bars represent standard error. Legend indicates
distance to road. ................................................... 68

FIGURE 18: Percent dead ﬂower buds of ‘Bluecrop’ blueberry bushes treated with
NaCl sprays on 19 Jan., 4 Feb., 18 Feb., 1 Man, and 19 Mar. 02, in May 2002. . . 86

FIGURE 19: Salt rinsed from twig surfaces of dormant ‘Bluecrop’ highbush blueberry
branches treated with NaCl sprays on 19 Jan., 4 Feb., 18 Feb., 1 Man, and 19 Mar. 2002.
Letters indicated signiﬁcant differences between treatment means (P S 0.05). No letters
indicated insigniﬁcant differences. ................................... 87

FIGURE 20: Relationship between rate of NaCl applied to soil in March and ﬂower bud
mortality in potted ‘Jersey’ blueberry bushes in May, 2002. ............... 89

REVIEW OF LITERATURE

Many roads in northern areas are treated with deicing salts, primarily NaCl.
Salting maintains safe travel surfaces during the winter, but this practice also may
damage roadside vegetation in the northern U.S. (Davidson, 1970; Sucoﬂ‘, 1975; Sucoﬁ‘
et al., 1975a; Bowers and Hesterberg, 1976; Sirnini and Leone, 1986; Herrick, 1988;
Bryson and Barker, 2002;), Canada (Hofstra and Hall, 1971; Hofstra et' al., 1979; Gibbs
and Palmer, 1994;), the UK. (Gibbs and Burdekin, 1986; Thompson et a1, 1986; Gibbs
and Palmer, 1994;), and European countries (Gibbs and Burdekin, 1983; Buschbom,
1980; Bogemans et al., 1989; Pedersen et al., 2000; Paludan-Muller et al., 2002).
Deicing salt usage may also result in concrete spalling (Amerhein et al., 1992; Shanley,
1994;), vehicular corrosion (van de Voorde and van Dijck, 1973; Buschbom, 1980;
Amerhein et al., 1992; Shanley, 1994; US. E.P.A., 1999; Robidoux and Delisle, 2001),
increased Cl' levels in surface waters (Zelazny et al., 1970; van de Voorde and van Dijck,
1973; Peters and Turk, 1981; Wilcox, 1986; Demers and Sage, 1990; Amerhein et al.,
1992; Shanley, 1994; Robidoux and Delisle, 2001) and damage to bridges (Amerhein et
al., 1992; US. E.P.A., 1999; Robidoux and Delisle, 2001).

Deicing salts may injure plants by runoff and salt loading of the soil (Langille,
1976; Thompson and Rutter, 1986) or when salt-laden spray or dust is generated by
trafﬁc and deposited directly on plants by wind (Sucoff, 1975). High soil salt levels tend
to occur in close proximity to roadways (Bowers and Hesterberg, 1976). The
consequences of high soil salt levels are well understood since saline soils limit crop
production in many arid areas of the world (Kaya and Higgs, 2002; Borsani et al., 2003).

Agricultural production on high salt or saline soils requires the use of tolerant species and
l

genotypes and careful water management (Maas, 1986). Less well understood is how
elevated soil salt levels affect the plant community structure of the roadside environment.
as well as regeneration of this community (Bicknell and Smith, 1975).

This work is focused on the effect of wind-blown salt spray on blueberries in
Michigan. Eaton et a1. ( 1999, 2002) and Percival et a1. (2002) described the effects of
deicing salts on lowbush blueberry. Damage to fruit crops other than blueberry has been
reported on apple (Hofstra and Lumis, 1974) and peach (N orthover, 1987).
Understanding the nature of deicing compounds and the conditions under which they
function best can help to understand where and when they should be applied.
Characteristics of Deicing Salts

In general, deicing salts work by depressing the freezing point and turn ice and
snow into slush. Solid salts (i.e., NaCl, CaClz pellets, et a1.) ‘bore’ through ice and snow
and produce a concentrated brine solution that spreads beneath the ice or packed snow
and breaks the bond to the pavement. Loosened ice and snow is easily removed by plows
or traffic.

Deicing agents must be water soluble to lower freezing points. Calcium chloride
(C302) is approximately 1.5 times more soluble than NaCl at 0 °C, has a lower freezing
point and will thus melt more ice. Both NaCl and CaClz are deliquescent (Roth and Wall,
1976). Calcium chloride generates more heat of solution (680.3 kJ'kg'l) than NaCl (102.8
kJ‘kg'l). Due to their individual chemical properties, the efﬁcacy of these two salts varies
under different environmental conditions (Roth and Wall, 1976). Sodium chloride is only
effective above 7 °C, whereas CaClz works best below this temperature (Roth and Wall,

1976). Calcium chloride is more effective over a broad range of temperatures, it reacts
2.

and achieves results more quickly than NaCl, but NaCl remains effective over longer
periods of time (Table 1).

Rock salt is 94 to 97% NaCl, and contains about 39% Na+ and 61% Cl'
(Schraufnagel, 1967). Calcium chloride contains about 36% calcium (CaH) and 64% Cl'.
Sodium chloride returns readily to a solid form, forming a residue of white dust that can
become airborne with trafﬁc movement and high winds. Calcium chloride tends to
remain as brine that is resistant to movement by trafﬁc and wind. This could mean that
under certain circumstances CaClz is more likely to run off into drains and ditches rather
than drift onto roadside vegetation.

Calcium magnesium acetate was ﬁrst identiﬁed by the US. Highway Dept. as a
possible deicing material in the late 19703 (MDOT, 1993). It is produced from dolomitic
lime and acetic acid. CMA has low corrosive potential, and is frequently blended with
NaCl at rates of 20% or more CMA to reduce corrosion.

Magnesium chloride attacks concrete more slowly than NaCl, and when used as
labeled, it reportedly does not harm vegetation (MDOT, 1993). However, it contains 17 -
56% more Cl' than other salt deicers, and 51% water. It leaves no residue and melts ice
down to -15 °C. Magnesium chloride begins deicing rapidly aﬁer application like CaClz,
but it may become diluted and lose efﬁcacy (MDOT, 1993).

Urea and potassium chloride (KCl) have similar deicing properties. Both do not
attack concrete by way of a chemical reaction. Urea works to -9 °C, and KC] works to
—11 °C, thus, they must be used at slightly higher rates. Urea has been used on airport
runways for deicing purposes. Sodium acetate is also known as ‘solid runway deicer’,

and is exothermic (evolves heat while melting ice). Sodium acetate has low toxicity, is

3

non-persistent and biodegradable, and has less impact on the biochemical oxygen demand
than urea. This deicer is active down to -18 °C and does not track indoor like other
deicers.
Toxicity of Deicing Communds

Information on the relative toxicities of various deicing compounds to woody
plants is limited. The majority of studies dealing with salt injury to plants have been
conducted with NaCl, the most widely used deicer. However, the effects of NaCl and
CaCl; on woody vegetation have been compared (Holmes, 1961; Walton, 1969;
Bogemans et al., 1989). Calcium chloride appears to be more phytotoxic than NaCl
when applied to the roots of Norway maple (A cer platanoides) during the dormant season
(Walton, 1969). Injury was attributed to direct chloride toxicity as well as other factors
that induced water stress in the trees. An earlier study (Holmes, 1961) also compared the
effects of CaClz and NaCl on six deciduous and evergreen tree species. Little
phytotoxicity was observed when these salts were applied to the roots over six years.
While a few trees exhibited damage symptoms, most appeared healthy, leading the author
to conclude that winter deicing practices in Massachusetts as practiced at the time
probably does little harm to trees. The author conceded that the applied salt solutions
may have run off and away from the tree roots due to frozen soil in the winter months,
thus sparing the tree of salt injury.

When equal doses of Cl“ were applied to the roots of spruce trees, uptake of Cl‘
was inhibited when Ca++ was present (Bogemans et al., 1989). Consistent with Dirr
(1975), these authors found that shoot and needle Cl’ concentrations correlated well with

visual damage symptoms. Twig Cl' levels of 0.8%, and Na}r levels of 0.5% typically
4

anested growth in the 12 deciduous and coniferous species tested (Lumis et al., 1976).
Although Cl' is preferentially accumulated in plant cells over Na+, NaJr may also reach
toxic concentrations inside plant cells (Dirr, 1976).

Chemical Properties of Sodium Chloride

The salt content of seawater is about 3.3%, and may range as low as 1.9%,
depending on location (Schraufnagel, 1967). Total annual salt production in the U.S. is
about 43 million tons per year, and 75% of this is used to make other compounds, such as
chlorine gas; hydrochloric acid (HCl); and sodium hydroxide (NaOl-I). For human
consumption, the oceans could provide us with our needs, but rock salt or halite from
underground deposits is the other principal salt source.

Sodium chloride has a molecular weight of 58.4 g, melting point of 804 °C, the
density is 2.17 g'mL", and a solubility of 36 g‘100mL'l H20 (Moxley, 1973). The
eutectic temperature (lowest possible freezing point of a saturated solution) is -21 °C.

Chlorine (C12) is a yellow-green, poisonous gas, but nearly always occurs as a
chemical combination with other elements (Schraufnagel, 1967). The earth’s crust
averages about 0.15% CI. Although humans can adapt to Cl' concentrations in drinking
water up to 2000 mg‘L", excessive Cl' can be harmful to people with heart or kidney
disorders (Schraufnagel, 1967). Under natural conditions in most humid parts of the
United States, groundwater contains less than 10 mg‘L'l Cl' (Hutchinson, 1970).

Chloride can be an environmental pollutant if Cl' levels are high in ponds or
wells. Twenty percent of farms in one study had ponds with Cl' levels greater than the
Public Health Service standard for potable water sources of 250 mg‘L'l (Hutchinson,

1970; Peters and Turk, 1981). Chloride greater than 250 mg'L" may also corrode
5

stainless steel and other metals (Schraufnagel, 1967), compromising industrial structures,
such as bridges, water treatment pipes, and equipment.

Sodium is a semi-white metal that reacts readily with other inorganic elements.
The earth’s crust is comprised of 2.6% Nat the sixth most abundant element. Sodium
compounds are generally very water soluble, and most Na+ related problems arise from
excesses as opposed to deﬁciencies. Clay and organic matter in soils are negatively
charged, and adsorb cations (positively charged ions) readily; this includes Na“,
magnesium (MgH), Ca++ and potassium (KT). Anions (negatively charged ions) are
repelled by the negatively charged soil surfaces. This means that Na+ cations can
accumulate in soils, whereas Cl' tends to leach through the soil proﬁle.
Salt Spray Injm to Plants

Salt spray from roads can directly damage adjacent vegetation (W esting, 1969;
Davison, 1970; Sucolf, 1975; Bowers and Hesterburg, 1976; Buschbom, 1980; Simini
and Leone, 1986; Eaton et al., 1999). Early work in Michigan concentrated on the effects
of CaClz, which was applied to gravel roads to control dust as early as the 19203 (Strong,
1944). Even though many roads canied fewer than 500 cars per day, traffic and
prevailing winds appeared to carry enough CaClz-laden dust onto nearby vegetation to
cause damage. Strong (1944) investigated whether this injury was the result of direct
contact with foliage or excessive soil levels. He observed that soil applications of C30;
injured trees, but species varied in their tolerance. Strong’s ﬁndings indicated that it was
not possible to reproduce the same damage symptoms under controlled conditions as
those seen in the ﬁeld. As well, the higher soil salt treatments frequently killed the plants

outright, although the Cl'-laden dust rarely did.
6

Davidson (1970) surveyed injury to four pine species: Austrian pine, Pinus nigra;
eastern white pine, Pinus strobus; red pine, Pinus resinosa; Scots pine, Pinus sylvestris
planted in 1966 along Michigan highways. About 40% of the trees were dead or severely
injured a year after planting. White pine appeared most sensitive to salt injury, Scots and
Red pine were intermediate, and Austrian pine was more tolerant than the other species.
The most severely affected plants were nearest to the highway in the splash and drift
zone. The author concluded that deicing salts caused the observed mortality, and that
Austrian pine appeared to be the most suitable Pinus species for highway median
plantings.

Some NaCl can leave treated roadways. As much as 10% of the deicing materials
applied to roads in Marquette County, Michigan became airborne on any day (Bowers
and Hesterberg, 1976). The researchers sampled soil at various distances from the road
for Na+ and Ca”. They also sampled white pine needles for the same cations at various
distances from the road and at varying heights within the tree. Injury to the trees was
related to Na+ levels in the soil, sampling depth, distance from the roadway, and time of
year (spring/fall). Sodium levels deposited on the needles increased up to 34m from the
roadway, and were highest on needles closest to ground level.

Numerous site characteristics contribute to the extent to which airborne deicing
salts damage roadside vegetation. The distance of the vegetation from the road, width of
the roadside shoulder, percent slope, elevation, and aspect (Piatt and Krause, 1974),
quantity of salt applied, application method, average daily trafﬁc (ADT), speed limit of
the road adjacent to susceptible, exposed vegetation, and prevailing wind speeds and

direction all inﬂuence injury levels (Sucoff, 1975). This may also explain why some salt-
7

sensitive vegetation at very exposed sites sometimes persist in spite of their high salt
exposure (personal observation). Salt spray is generated relative to the quantity of
deicing material applied, and this will vary with winter severity (i.e., greater snow
accumulations typically require more deicing salt applications, resulting in increased salt
spray levels). Damage is usually consistent with patterns of deicing salt distribution; i.e.,
one can expect to ﬁnd more damage to blueberry bushes on heavily traveled divided
highways than in ﬁelds on the secondary highways, or on minor secondary roads.
However, dramatic differences in damage to blueberry plants along minor roads can
appearﬁ'om one year to the next, again depending on winter severity.

As trafﬁc volumes and speeds increase, more salt spray will be generated. A shift
in the usual direction of the prevailing winds can effectively evacuate windbome salts
away from susceptible vegetation.

Deicing salts are applied to many Michigan roads to maintain safe road surfaces
during the winter. There are 193,121 linear kilometers of highway in Michigan (MDOT,
1993). Most roads are maintained by local or countyjurisdictions in Michigan. The
Michigan Department of Transportation (MDOT) maintains about 8% of roads (MDOT.
1993). During the winter of 1991-92, the last date for which accurate data were
available, MDOT applied 401,178 metric tons of NaCl (MDOT, 1993), a rate of about 28
metric tons/equivalent for the entire winter, with an equivalent being deﬁned as 1.6
kilometers of 7.3 meter-wide, two-lane road surface (MDOT, 1993). While it has not
been possible to obtain the quantity of deicing salt applied in Ottawa County, data from

Macomb County, Michigan, indicate that annual salt use may vary by more than 200

percent (Mykytiak, pers. comm.)

Small trees are typically damaged at greater distances from the road than large
trees (Piatt and Krause, 1974). Roadside vegetation at higher elevation relative to the
road is also less damaged (Piatt and Krause, 1974). Soils down slope of the roadway also
typically contain higher Cl' levels, but distance to the farthest affected vegetation also
increases with increasing slope. It is believed that Cl' dispersal is facilitated by the
increased water movement on steeper slopes (Piatt and Krause, 1974).

Woodcock (1950) used test plates of varying shapes to simulate leaves and
showed that long, narrow plates exposed in a salt laden air stream accumulated much
more salt per unit area than broad plates. Edges appeared to collect more salts than
centers, and very few of the smaller salt nuclei (droplets of concentrated salt water that
weigh 10"4g or less) were deposited on broad surfaces. This suggests that narrow twigs
and leaves (evergreen needles) may collect more salt than broad leaves.

Salt damage to roadside turf is less commonly reported than injury to woody
plants. This is somewhat puzzling because the long and narrow foliage of many grasses
would be expected to intercept large quantities of salt in the absence of snow cover.
There is some conﬂict as to which form of vegetation is more salt sensitive, woody or
herbaceous. Holmes (1961) reported grass species to be more sensitive than trees,
observing that grass underneath some sugar maples sustained more damage from high
soil salts than the trees themselves. Cordukes and Parups (1971) reported considerable
Cl' tolerance of all 12 grass cultivars tested, representing eight species. Others have
concluded that woody plants sustain more damage than herbaceous species (W esting,

1969; Davison, 1975; Sucoff, 1975; MDOT, 1993).

Physiological Ba_sis of Salt Injury to Woody Plapt§

Woody plants absorbed less salt when exposed to salt spray in the middle of the
winter when they are ﬁrlly dormant than when they began growing in March and April
(Rostra and Lumis, 1974; Lumis et al., 1976). Lumis et a1. (1976) found the highest
internal shoot Na+ and Cl' levels in the dormant buds of Norway maple (A cer platanoides
L.), beech (Fagus grandifolia Ehrh.) and lilac (Syringa vulgaris L.) Button (1964)
reported increasing levels of Na+ and CI' in tissues and sap of sugar maple trees with
increasing exposure to roadside drainage. Symptoms of decline were most severe on
trees exposed to roadside drainage. A carry-over of accumulated chloride from one
season to the next was thought to contribute to rapid accumulation of critical quantities of
salt in the foliage. However, some trees with very high tissue Cl' concentrations
exhibited no symptoms of injury. Simini and Leone (1982) found that most actively
growing plants absorbed more salt when exposed to shorter photoperiods, higher relative
humidities, and lower temperatures. However, salt spray injury to dormant Norway
maple (A cer platanoides ‘Emerald Queen’) buds was not inﬂuenced by air temperature
and humidity (Barrick and Davidson, 1980). They also concluded that injury in dormant .
tissue was more closely related to penetration of phytotoxic ions than to osmotic stress.

High exogenous salt concentrations may cause an imbalance of cellular ions
resulting in ion toxicity and osmotic stress (Chang-Le et al., 2003). This type of salt
stress can also impair electron transport within the various subcellular compartments
leading to the generation of reactive oxygen species, such as hydroxyl radicals, and the
superoxide radical (Chang-Le et al., 2003). Whether this occurs when dormant plants are

exposed to salt spray is not known. Caya and Higgs (2002) found that applying small

10

amounts of calcium nitrate to saline soils reduces the effects of salts on chlorophyll
concentrations, plant growth, and fruit yield, and increased membrane permeability of
cucumber (C ucumis sativus).

lobe] and Nighswander (1990) hypothesized that salt spray enters dormant
Austrian and red pine needles through the stomata, and that the resulting necrosis was
caused by accumulation of phenolic compounds produced as a defense mechanism. This
may lead to the degradation of the cytoplasm, the disappearance of organelles, the release
of vacuolar contents, damage to membranes and death of mesophyll cells (Zobel and
Nighswander, I990). Barrick et al. (1979) concluded that differences in sensitivity of
Austrian, scots, and white pine to salt spray injury reﬂected different protoplasmic
sensitivity rather than penetration patterns of Na+ and CI' ions. Sucoff(1975) believed
salt entered dormant deciduous twigs via bundle traces. It is unknown if Ienticels could
also provide an entry court for salts into dormant twig tissues.

Twigs and stems of woody plants exposed to wind-blown salt spray often
exhibited dieback (Davidson, 1970; Lumis et al., 1973; Dir'r, 1975; Sucoff, 1975; MDOT,
1993). Cold injury caused similar symptoms. Some investigators speculate that salt
spray causes more injury to vegetation than run-off and soil accumulation of deicing salts
(Hofstra et al., 1979), while others argue that woody plants are more sensitive to soil
salinity than salt spray (Thompson and Rutter, 1986a). Thompson and Rutter (1986)
observed that some plants of all species studied died as a result of soil salinity, while salt
spray killed only a small proportion of shoots which were replaced by the development of
latent buds (witches-broom development). The sensitivity of plant species to salt spray is

not necessarily related to their tolerance to excess soil salt levels (Thompson and Rutter,

ll

1986).

How salt spray injures aerial plant parts is not clear. Injury may result ﬁ'om toxic
C1' or Na+ in the tissues (Dirr, 1975). Internal shoot concentrations of sodium and _
chloride were correlated with injury to apple (Malus sylvestris) twigs (Hofstra and Lewis,
1975), suggesting toxicity. However, internal Na+ and/or Cl' levels are not consistently
correlated with the relative sensitivity of the species. Paludan-Miller et al. (2002) studied
the effects of NaCl applied to the soil or above ground plant parts of seedlings of four
deciduous tree species (maple, Acer pseudoplatanus; beech, Fagus sylvatica; horse
chestnut, Aesculus hippocastanum; and basswood, Tilia cordata). While the four species
differed in their responses, the amount of injury could not be predicted based on foliar
concentration of Na+ and Cl".

Injury may also be related to water loss associated with salt exposure. However,
Northover (1987) found no evidence of desiccation to peach shoots killed by salt spray.
Westing (1969) observed that abundant rainfall in the northern states helps plants avoid
salt injury by ﬂushing salts out of the soil proﬁle and away from plant roots, and points
out that the high soil salt levels in the western U.S. results partly from low rainfall.
Button (1964) provided evidence that saline soils can have a gradual, cumulative negative
effect on roadside sugar maples, even at low concentrations. Trees in advanced states of
decline had low twig and leaf CI' levels. The author accounted for this paradox by
theorizing that translocation, transpiration and metabolism had already declined to the
extent that during the season before sampling, the trees had taken up little water and little
chloride. If this trend were operating for at least several years prior to Burton’s survey,

then the cycles of leaf abscission coupled with negligible Cl' uptake might have removed

12

enough Cl' from the twig and leaf samples the author collected to account for the low Cl'
levels. Lumis et al. (1976) theorized that salt accumulation in several species resulted
from accumulation from previous years’ salt applications. The annual increases in
internal salt concentration helps explain the gradual decline in vigor observed by several
workers (Button, 1964; Pedersen et al., 2000). This could mean that Na+ and C1' are not
being completely removed from the plants by leaf abscission in the fall.
Woody Plant Cold Hardiness

Since salt exposure reduces the cold hardiness of various woody plants (Sucoff,
1975), and causes similar symptoms as lethal winter temperatures, salt spray injury may
be analogous to winter injury.

Low temperature stress limits crop production in many areas of the world (Chen,
1994; Howell, 2000), and includes chilling stress and ﬁ'eeze stress (Chen, 1994).
Chilling injury can occur at temperatures of 10 °C to 15 °C. Freezing low-temperature
stress occurs when temperatures fall below 0 °C; and is associated with ice formation
within plant tissues (Chen, 1994). Plants have evolved the ability to acclimate to cold
temperatures as a response to seasonal changes in climatic patterns, thereby allowing
them to complete their life cycles in spite of these challenges (W isniewski and Bassett,
2003). Symptoms of freezing injury include frost cracks and sun scalding of tree trunks,
blackheart in shoots of trees and shrubs, winter burn (evergreen foliage), soil heaving and
crown kill damage of herbaceous plants, autumnal and spring frost injury of succulent
annuals, and mid-winter kill of dormant ﬂower buds (W eiser, 1970).

Weiser (1970) described the sequences of freezing death in hardened bark cells

based upon analysis of results from freezing curve, calorimetric, and microscopic studies.

13

supercooling—extracellular freezing in non-living xylem cells, and between cells-uapid
growth of ice throughout stem, resulting in—wn exotherm (release of a substantial
amount of heat of fusion from free-water) resulting in a warming of the tissue
temperature from the supercooling point (-2 °C to -8 0C) to a crest at the freezing point of
the available water in the stem tissues (-0.3 °C to -1 °C)—additional cooling after the ﬁee
water is frozen—+movement of protoplasmic water out of cells to extracellular ice nuclei,
as a response to the extracellular aqueous vapor pressure deﬁcit-ta second pronounced
exotherm, followed by decreasing tissue temperature and a continuous slow migration of
cellular water out to extracellular ice nuclei—sprotoplasmic shrinkage, plasmolysis, and
concentration of solutes in the cell—ta continued slow movement of cellular free water
out to extracellular ice as the temperature decreases—*3 calorimetric decrease which
indicates that movement of water out of the cell (freezing) is halting—ra third
exothenn—>protoplasmic granulation—enecrosis.

Cold hardiness is a complex trait controlled by many genes (Chen, 1994;
Wisniewski and Bassett, 2003), and changes throughout the dormancy period
(W isniewski and Bassett, 2003). Detailed reviews of cold hardiness at the molecular
level are available (Chen, 1994; Wisniewski and Bassett, 2003).

How salt compromises cold hardiness is not understood, but could involve cell
membrane changes that result in more succulent and less hardy tissues (Sucoff and Hong,
1976a), or an increase in tissue sensitivity to NaCl associated with low temperature stress
(Sucoff and Hong, 1976a). Even small losses in cold hardiness can cause signiﬁcant crop
losses, because each cold stress event can have cumulative effects in ﬂower bud loss, or

damage to woody tissues (Howell, 1988).

14

Freezing injury may begin when ice crystals form within the intercellular spaces
of plant tissue (Chen, 1994). This will occur when the plant tissue is exposed to
temperatures below the freezing point of the tissue. Live plant cells are surrounded by a
hydrophobic plasma membrane, preventing the growth of ice crystals into the cytoplasm.
Thus, the ice is absent within the cell, but may continue to spread throughout the
intercellular space. This is known as extracellular ﬁeezing. If the temperature drops
below a critical lethal point, ice crystals form rapidly inside the cytoplasm (intracellular
ﬁeezing), rupturing membranes and killing cells. When tissues thaw, cytoplasm leaks
from cells, and tissues lose of turgor. Necrotic tissues may appear ‘water-soaked’ due to
electrolyte leakage (Howell and Weiser, 1970). Sakai (1973) observed a lack of
intracellular freezing in the twigs of extremely cold hardy taxa, such as poplar (Populus
gelricha) willow (Salix sachalinensis) and white birch (Betula pubescens).

Freezing rate affects the amount of injury to plant tissues (Weiser, 1970; Sakai,
1973; Vorsa, 1992). Rapid temperature decreases result in more injury. Temperature
decreases seldom exceed 1.0 to 2.0 °C/hour (Flinn and Ashworth, 1994a), although
decreases as much as 20.9 °C in one hour were recorded which resulted in devastating
blueberry ﬂower mortality in numerous ﬁelds in New Jersey (V orsa, 1992).

Differential thermal analysis (DTA) is a useful tool in estimating the cold
hardiness of woody plant tissues (W isniewski and Bassett, 2003). Investigators
performing DTA will often ‘seed’ or induce ice crystal formation in the tissue by
wrapping tissue samples in moistened cheesecloth, or misting the plant tissue with water
before DTA begins (W armund, 1993; Warmund and English 1995; Warmund and

English, 1998). The process of ice formation is known as ‘ice nucleation’. The non-

15

lethal high-temperature exotherm represents extracellular ice formation (Warmund et al.,
1991). This is followed by one or more low temperature exotherms, which are associated
with intracellular ﬁ‘eezing of supercooled water in the ﬂower primordia. Thermal
analysis (TA), as well as DTA, is usually employed to measure cold hardiness of tissues
that avoid ﬁ'eezing by supercooling, such as peach (Prunus persica) and cherry (Prunus
cerasus) ﬂower buds.
Supercooling

Supercooling is a freeze-avoidance mechanism (Sakai, 1979; Wisniewski and
Bassett, 2003), whereby tissues or organs are able to retain water in a liquid phase at low
temperatures by remaining free from internal and heterogenous ice nuclei, and isolated
from the nucleating effect of extracellular ice. Supercooling occurs in ﬂower buds,
xylem ray parenchyma cells [XRPCs], and some other tissues, and occurs at higher
temperatures than deep supercooling. The detection of low temperature exotherms
(LTEs) can accurately estimate the level of cold hardiness in many, but not all, species
that deep supercool (Lindstrom et al., 1995).
Deep Suxrcooling

Deep supercooling is a freeze-avoidance mechanism that occurs in certain stem
tissues such as axial and XRPCs, as well as ﬂower buds, (Quamme, 1991), and differs
from supercooling by occurring at lower temperatures (below -20 °C ). This is
characteristic of many woody plants, but especially deciduous hardwoods (Quamme,
1991). Intracelluar freezing of the deep supercooled water in these tissues will sustain
permanent injury as temperature decreases below a nucleation point (Quamme, 1991).

Andrews and Proebsting (1986) found no effect of photoperiod on the development of the

16

deep supercooling mechanism in peach and sweet cherry.

Deep supercooling remains a rather elusive phenomenon, in that apparently the
properties that allow deep supercooling to occur seem to rely on the structural
organization of the tissue/organ (W isniewski and Bassett, 2003). Quamme (1976)
posited that the spontaneous nucleation temperature of supercooled xylem water
correlated with the northern limit of apple (Malus pumila) and pear (Pyrus communis)
production in North America. Four exotherms occur as apple twigs are cooled, and the
fourth was associated with the freezing of xylem and pith tissues, and coincided with the
killing temperature of xylem ray and pith parenchyma cells (Quamme et al., 1972).
Apple bud and bark tissues were hardier than xylem in mid-winter, and that pith and
xylem were hardier than bark and buds in early autumn and late spring (Quamme et al.,
1972).

In order to rapidly determine cold tolerance of woody plants in the ﬁeld, a method
for determining ‘LTso’, or the temperature at which 50% of ﬂower buds will be killed,
has been developed (Bittenbender and Howell, 1974; Proebsting and Sakai, 1979).
Bittenbender and Howell’s adaptation of the Spearrnann-Karber formula makes this
computation easy, even for uneven temperature decrements. DTA is often useful for
determining LTso, but can require many (200 or more) ﬂower buds (Proebsting and
Sakai, 1979). Field mortality levels are often accurately bracketed by determinations of
LTso , but not always (Bittenbender and Howell, 1974; Proebsting and Sakai, I979; Flinn
and Ashworth, 1994a; Wolf and Cook, 1994).

Hardiness has been associated with maximum tolerance to desiccation (V ertucci

and Stushnoff, 1992). Hardiness is also hypothesized as being dependent upon the

17

moisture-retaining power of the cell (Vertucci and Stushnoff, 1992), depending on the
tissues. Bittenbender and Howell (1975) found that dehydration of bluebeny ﬂower buds
increased hardiness, and increased moisture reduced hardiness. At 25 °C, hardiness was
apparently unaffected by moisture. This implies that a small amount of NaCl could
remove enough free cellular water so as to decrease the incidence of intracellular
freezing, which could increase cold hardiness. It is just as likely that exposure to
increasing NaCl concentrations could remove enough cellular water to desiccate and kill
cells. This would be more devastating to ﬂower buds than woody bark tissues, as the
ﬂower buds are the critical sensitive tissues (Bittenbender and Howell, 1976; Hancock et
al., 1987).

Other factors affect the cold hardiness of woody plants. Flore et al. (1983) found
that shading during the growing season reduced cold hardiness in sour cherry and peach,
possibly by reducing photosynthesis and carbohydrate accumulation. Howell (1988)
reported the same ﬁnding in grape (Vitis spp.), and concluded that vine hardiness can be
viewed as a carbohydrate sink, albeit a weak one. Proebsting and Mills (1973) reported
increased survival of ﬂower buds after exposure to ethephon [(2-chloroethyl)phosphonic
acid]. Delayed bloom, as well as anthesis, caused by ethephon treatment was attributed
to increased yields. Proebsting and Mills (1974) found that ‘Bing’ cherry trees (P.
avium) treated with gibberellic acid (GA3) had reduced hardiness, depending on the time
of application because of the dormancy-breaking and growth stimulating properties.
Raese (1996) found that summer sprays of CaClz or calcium nitrate [Ca(N03)2] increased
cold hardiness of ‘Anjou’ pear trees (Pyrus communis). This study was conducted over

many years in Washington State, where severe winter injury occurs about every 8 years.

18

Raese (1996) suggested that calcium is an important component of plant cells, and thus
may be important in maintaining cold hardiness of certain plant tissues.
Bluebegy Cold Hardiness

Commercial production of blueberries in Michigan is generally limited to
southern Michigan because winters are too severe in more northern climes. Even in the
southern production area, annual winter injury ranges from slight to severe, so even a
slight reduction in the cold tolerance of ﬂower buds can result in substantial yield losses.
Blueberry bushes may be more susceptible to salt spray injury than some other woody
species because the ﬂower buds are borne on the exposed terminal portions of the
previous year’s growth. Each ﬂower bud can give rise to from four to 18 fruits
(Hancock, pers. comm.), depending on the cultivar.

The ability to acclimate rapidly and early in the fall is an important trait for
highbush bluebeny cultivars grown in the North Central states (Fear and Lawson, 1987).
Highbush blueberry undergoes a rest period, identiﬁed as a three-stage process (onset,
deep rest, and release from dormancy), while simultaneously developing cold hardiness
(Gough, 1994). The rest phase is a period of dormancy, and the plant will not respond to
external stimuli until certain internal conditions have been met; i.e., the chilling
requirement being the main factor. External conditions such as low temperatures and
decreasing photoperiod are thought to trigger the onset of rest (Gough, 1994). The plant
begins to shutdown because of the inﬂuence these external factors have on respiration,
plant growth regulators, and metabolism (Gough, 1994). Roots are reported to maintain
growth into mid-winter and enter a quiescent state rather than dormancy, in response to

low soil temperatures and the lack of available water (Gough, I994). The chilling

l9

requirement is the critical amount of time that blueberry must be exposed to temperatures
below 7 °C in order to resume growth (Gough, 1994). The chilling requirement is
eultivar-dependent, and there is disagreement regarding the actual temperature below
which the chill requirement is best satisﬁed (Gough, 1994; Eek, 1988). Northern
highbush cultivars typically require a greater number of chilling hours, from 800 to 1100
chilling hours (Eek, 1988), whereas southern, low-chill, highbush cultivars adapted to
central Florida require less than 400 hours (Gough, 1988). A ‘chill hour’ is deﬁned as the
amount of time a dormant plant is exposed to the minimum low temperature that satisﬁes
the chill requirement. Vegetative buds may have a higher chilling requirement than ﬂoral
buds (Eek, 1988; Gough, 1994), since they often open later than ﬂoral buds in the spring.

New growth cannot commence in the spring until the chilling requirement has
been met. The chill requirement is often satisﬁed before external conditions are
conducive to growth in the northern blueberry production areas. However, plants cannot
resume growth until external conditions will allow ﬂower and vegetative buds to emerge
from the bud scales. Spring growth and fruiting will be less vigorous on those plants that
have only marginally met their chill requirements, and may be even more vigorous on
those that have received more than their necessary chill requirements (Eek, 1988; Gough,
1994).

Bittenbender and Howell (1976) and Johnston (1939), reported highbush
bluebeny is most susceptible to freezing injury in the spring. The reason for this is late-
spring frosts are common in Michigan and, at this stage in their development, ﬂower buds
have usually lost hardiness to the extent that the bud scales are being pushed open by the

emerging ﬂowers. Blueberry sites are also typically low areas where cold air

20

accumulates. Olson and Eaton (2001) also observed spring freeze damage to lowbush
bluebeny ﬂower buds that occurred in Nova Seotia, Canada. Bittenbender and Howell
(l 976) reported that dehardening occurred in highbush blueberry between mid-January
and early March in Michigan, and that the ovaries are the tissues most sensitive to cold
temperatures. Proebsting (1970) reported that mid-winter ﬂower bud hardiness declined
as much as 0.9 °C/hour at temperatures above -2.0 0C. Doughty and Hemmeriek (I 974)
reported that the same was true for highbush blueberry, and that certain nutrient sprays
(i.e., ZnPK, ZnPCa and ZnPCaMn) may reduce freeze injury to ﬂower buds, although
differences were noted among tested cultivars. These authors also reported that bushes
treated with ZnPN and ZnPKCa showed serious injury to ﬂower buds and wood.

The position of ﬂower buds on blueberry twigs also affects their hardiness.
Terminal buds are less hardy than more basal buds in secondary, tertiary and quartemary
positions (Bittenbender and Howell, 1976; Hancock et al., 1987; Clark et al., 1991).
Hancock et al. (1987) observed a positive inverse linear relationship between percent
brown ovaries to bud position since the apical buds typically begin developing earlier in
the spring than more basal buds (Hancock et al., 1987). More fully developed buds
(terminal buds, in most cases) may contain more water that increases the likelihood of
intracellular freezing (Bittenbender and Howell, 1976).

If terminal buds are less hardy than more basal buds, then a high number of
ﬂower buds per stem may increase a blueberry cultivar’s productivity, regardless of its
ability to tolerate freezing low-temperature stress (Bittenbender and Howell, 1976). It
would seem that this should be a goal for blueberry breeders interested in producing more

cold-tolerant cultivars (Hancock et al., 1987).

21

Clark et al. (1991) also observed that origin of gerrnplasm, and the season of
ﬂower bud development affect the ability of blueberry ﬂower buds to tolerate cold.
Southern highbush bluebeny cultivars were more cold tolerant than rabbiteye cultivars
(in which ﬂower buds may form during the fall growth ﬂush, or during the spring growth
ﬂush) at similar stages of ﬂower bud development (Clark et al. 1991).

In highbush blueberry, the low-temperature exotherm (LTE) is associated with
xylem injury, rather than bark injury (Quamme et al., 1972a). Xylem, phloem and
eambiurn injury in highbush blueberry is not as important for survival as bark injury, and
bark injury occurred at a higher temperature than xylem, and was not associated with an
exotherm (Quamme et al., 1972a). Flinn and Ashworth (1994) observed that highbush
bluebeny lacks detectable low-temperature exotherms under conditions of slow-cooling
(-2.0 °C/hr). These same authors also found that DTA was incapable of detecting LTEs
in ‘Berkeley’ ﬂower buds attached to 5 cm stem segments, and cooled at a rate of 2.0
°C/hour (Flinn and Ashworth, 1994). This is signiﬁcant because the relationship between
ice distribution and vascular development has been studied only in those species that
exhibit the low-temperature exotherm (Flinn and Ashworth, I994). Flinn and Ashworth
(1994a) studied the rate of vascular development in highbush bluebeny, and noted that
both acclimated and deacelimated ﬂoral buds possessed long, narrow extracellular splits
in bracts, bud and ﬂoret scales; nonacelimated buds were deﬁcient in this feature. They
observed that mature. continuous vessels had differentiated further toward the apex of
corollas into December. Fuehsin stain was used to detect this anatomical development,
and vascular development was suspended from December through the end of February.

The highbush blueberry cultivar ‘Berkley’ is not separated from xylem at the

22

onset of dormancy, and thus cannot supercool (Howell, pers. comm.) As a result, it is
less hardy under Michigan conditions than some other cultivars.

By mid-April, deacelimated ﬂorets were four times wider and longer than
acclimated ﬂorets, because of water uptake (bud swelling). A densely stained vascular
system was observed to spread throughout the ﬂorets, and all portions of the ﬂorets were
apparently connected to the parent plant via mature xylem (Flinn and Ashworth, 1994a).
Sakai (1979) also found that ﬂower buds of ﬂowering dogwood (Cornusﬂorida) had
higher water content in the spring (66% water, fresh weight) than did winter buds (33%
water, fresh weight). The latter author also reported no detectable LTEs in these spring
buds.

Bittenbender and Howell (1 975a) developed useful models to describe the level of
cold hardiness obtained in highbush blueberry. It was found that increasing photoperiod
correlated better with dehardening. Such models can be of value in selecting a planting
site, or evaluating seedling cold hardiness.

Quamme (1978) observed masses of ice formation in bud scales and ﬂower bud
axis of peach ﬂower buds, but not the primordia. He proposed the existence of two
barriers that operated below —10.0 °C that prevented external nucleation of supercooled
tissue, and that ultimately an explosive growth of ice formation killed ﬂower primordia,
presumed to be intracellular ice formation (Quamme, 1978). He also proposed the
mechanism in supercooling involves migration of water from the bud axis to the scales,
resulting in a dry region (or sink) which may function as a barrier against ice growth from
the peduncle, while water in the primordia does not migrate during cooling of the ﬂower

buds. Graham and Mullin (1976) had previously suggested that the water content of

23

Rhododendron ﬂower buds is related to their exotherm temperature, and that ﬂower bud
scales may function as an ice sink for reduction of water in the ﬂorets

Ishikawa and Sakai (1981) studied the mechanisms involved in supercooling in
Rhododendron ﬂower buds, drawing on the earlier work by Graham and Mullin (1976)
and Quamme (1978). The former authors reported the exotherm temperature in excised
Rhododendron ﬂorets was inversely proportional to the water content. They also found a
decrease in water content of ﬂorets and peduncle of R. japonicum, and an increase in that
of the scales. These authors dissented with the use of the term ‘supercooling’ to describe
the strategy employed by ﬂorets to survive cold stress, since this involves a migration of
water and subsequent dehydration, as in extracellular freezing.

In the early/middle 19903 blueberry growers in west Michigan began observing
severe loss of ﬂower buds on their plants closest to the nearest salted roads, with
subsequently reduced yields. Distance to the nearest road appeared to be closely related
to ﬂower bud mortality. This thesis was initiated to study this phenomenon in order to
determine whether deicing salts were contributing to the loss of ﬂower buds of blueberry

plants in West Michigan.

24

 

Table 1. Comparison of various deicing chemicals. Note: For general comparison only;
published values of lowest effective temperatures vary widely.
’BOD = Biochemical oxygen demand.

 

Lowest
effective
Deicing tem
chemical (°C) General characteristich Cost/metric ton (S)Y
Sodium -8 -Harrns vegetation 33
chloride -10 — 25% can leave the roadway after
application
-Can cause environmental pollution
-Chemieally attacks concrete
-Degrades soil structure
-Contains cyanide (sodium
ferrocyanate - toxic to ﬁsh)
Calcitun -25 -No cyanide 220
chloride -Works faster
-Less harmful to soil structure
-Exothermic
-More corrosive than MgClz
-6x more expensive than NaCl
-Harms vegetation
Potassium -11 -Less harmful to vegetation 240
chloride -No cyanide
-Does not attack concrete
-Can be slow-acting
-Needs to be used at slightly higher
rates
Magnesium -25 -Less harmful to vegetation 240
chloride -No cyanide
-Does not attack concrete
-Chemically attacks concrete
-May become diluted and ineffective
-Contains 17 — 56% more chlorides
than other ‘salt’ deicers
Continued on next page

 

25

Table 1. Continued

Lowest
effective
Deicing tern
chemical (°C) General characteristich Cost/metric ton (S)Y
Sodium Below -18 -Does not track 1610 — 1920Z
acetate -Exothermic
-Biodegradable
-No cyanide
-Does not attack concrete
-Slightly difﬁcult to work with (can
cake or dust eas'gy)
Urea -10 -Contains no chlorides (less corrosive) 280
-No cyanide
-Does not attack concrete
-Can increase BOD
-Needs to be used at slightly higher
rates
Calcium Below ~18 Biodegradable 712 - I889z
magnesium -Adheres to pavement longer
acetate -Less toxic to aquatic life
-No cyanide
-No new application equipment
necessary
-Improves soil structure
-Less harmful to vegetation
-20x + more expensive than NaCl
-Can be slower-acting under certain
conditions
-Can increase BOD
-Blown easily by wind
-Cakes easily
-Not as effective below -5 °C

YCryotech Deicing Technology (2004)

ZMDOT (1993)

26

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35

CHAPTER II

FLOWER BUD MORTALITY AND NaCl LEVELS IN BLUEBERRY

FIELDS ADJACENT TO SALTED ROADS IN MICHIGAN

36

ABSTRACT
FLOWER BUD MORTALITY AND SALT LEVELS IN BLUEBERRY FIELDS

ADJACENT TO MICHIGAN ROADS TREATED WITH DEICING SALT

Blueberry ﬁelds adjacent to roads in southwest Michigan exhibit abnormally high
levels of ﬂower bud mortality and twig dieback, even following relatively ‘mild’
Michigan winters. This work was conducted to determine if this injury was caused by
deicing salts (primarily NaCl) blown directly onto bushes. During these surveys, ﬂower
primordia injury was evident by mid-January, and increased throughout the winter.
Flower bud mortality was recorded in the spring in several locations within 12 farms, and
mapped graphically with Global Positioning System (GPS) technology. Survey farms
were adjacent to salted highways and secondary roads. The numbers of living and dead
ﬂower buds were counted on two plants at varying distances to the salt source at bloom-
time, in May. The greatest number of dead ﬂower buds occurred closest to the most
heavily traveled roads.

Flower bud mortality was dependent upon minimum daily temperatures and the
orientation to and distance from the salted road(s). Dormant twig sampling for ﬂower
primordia mortality and salt deposition indicated that ﬂower primordia mortality was
generally greatest on twigs sampled close to salted roads. Lower amounts of salt were
found on twigs from plants farther away from the salt source, or from farms west of

major salted roads.

37

Salt deposition on twigs often increased through the winter months, but decreased

in those months that experienced precipitation events, which apparently rinsed away

salts.

38

INTRODUCTION

Michigan is the largest producer of blueberries in the nation, averaging 27 million
kilograms per year (1996 — 2000), with a mean value of 45 million dollars (MASS,
MDA, 2001). There are about 620 blueberry farms and 6,800 hectares in Michigan
(ERS, USDA, 2004). Most of the production occurs along Lake Michigan, ﬁ'om Berricn

County north to Muskegon County.
I In 1999, several Michigan blueberry growers in Ottawa County expressed
concern about low yields and twig dieback on plants close to roads treated with deicing
salts, primarily NaCl. Preliminary observations in 2000 indicated that high levels of salt
were deposited on twigs during the winter and that ﬂower primordia mortality was
greatest close to the road, suggesting that injury may result from exposure to deicing salt
applied to the roads.

This was not the ﬁrst report of deicing salt injury to woody vegetation in
Michigan. Davidson (1970) reported that Pinus spp. vary in their sensitivity to deicing
salt. Barrick et a1. (1979) hypothesized that differences in the sensitivity of Pinus spp. to
deicing salt spray may relate to morphological differences in needles.

Deicing salts may injure plants by runoff and salt loading of the soil (Langille,
1976; Thompson et al., 1986) or when salt-laden spray or dust is generated by traffic and
deposited directly on plants by wind (Sucoff, 1975). Salt spray is generated relative to
the quantity of deicing material applied, and this will vary with winter severity (i.e.,
greater snow accumulations typically require more deicing salt applications, resulting in
increased salt spray levels). Deicing salt spray injmy to woody vegetation has been

reported in the northern United States (Davidson, 1970; Sucoff, 1975; Bowers and

39

Hesterberg, 1976; Simini and Leone, 1986; Herrick, 1988; Bryson and Barker, 2002),
Canada (Hofstra and Hall, 1971; Hofstra et al., 1979; Northover, 1987), European
countries (Buschbom, 1980; Gibbs and Burdekin, 1983; Bogemans ct al., 1989; Pedersen
et al., 2000; Paludan-Muller et al., 2002), and the United Kingdom (Thompson et a1,
1986; Gibbs and Palmer, 1994).

Twigs and stems of woody plants exposed to wind-blown salt spray often
exhibited dieback (Davidson, 1970; Lumis et al., 1973; Dirt, 1975; Sucoff, 1975; WOT,
1993; Eaton, 1999; Eaton etal., 2004). Some investigators speculate that salt spray
causes more injtu'y to vegetation than run-off and soil accumulation of deicing salts
(Hofstra et al., 1979), while others argue that woody plants are more sensitive to soil
salinity than salt spray (Thompson and Rutter, 1986). Thompson and Rutter (1986)
observed that some plants of all species studied died as a result of soil salinity, while salt
spray killed only a small proportion of shoots which were replaced by the development of
latent buds (witches-broom development). High soil salt levels can cause severe dieback
of tree crowns and branches, whereas deicing salt spray seldom affects woody plants to
this degree. The sensitivity of plant species to salt spray is not necessarily related to their
tolerance to excess soil salt levels (Thompson and Rutter, 1986). How salt spray injures
aerial plant parts is not clear. Injury may result ﬁ'om toxic C1“ or Na+ in the tissues, or
from desiccation of cells (by osmosis) (Dirr, 1975). Internal shoot concentrations of Na+
and CT were correlated with injury to apple (Malus sylvestris) twigs (Hofstra and Lumis,
1974), suggesting toxicity. Tissue sampling may provide evidence for Na+ and/or CI'
toxicity; however, internal Na+ and/or Cl' levels are not consistently correlated with the

relative sensitivity of the species. Unfortunately, there are conﬂicting reports regarding

4O

the correlation between observed phytotoxicity, and toxic ion levels in plant tissues
(Button, 1964; Sucoff, 1975; Pedersen et al., 2000).

Eaton et al. (1999) investigated deicing salt injury to lowbush blueberry (V.
angustifolium Ait.) next to highways in Nova Seotia, Canada. They found that ﬂower
numbers and yield increased with distance ﬁom the road, and were inversely related to
the concentration of salt on the shoots. They also found that plants protected by plastic
shelters had more live ﬂowers and higher yields than exposed plants at the same distances
from the road (Eaton et al., 1999).

Considerable amounts of deicing salts may leave treated roadways as drift
(Sucoff, 1975; MDOT, 1993), and travel away from the roadside (Moxley, 1973; Sucoff,
1975; MDOT, 1993). Pre-treating the deicing salts before application with liquid calcium
chloride or some other brine decreases the amount of salts leaving the roadway (MDOT,
1993). If as much as 10% of deicing salt leaves roadways after application (Bowers and
Hesterberg, 1976), and 100 to 141 kg NaCl are applied per kilometer of divided highway
in Ottawa County (personal communication, Ottawa County Road Commission,
December, 2001), this means that anywhere from 10 to 14 kilograms of NaCl are leaving
the roadway soon after every application.

Vegetation adds to roadway aesthetics, reduces glare, and prevents erosion
(Westing, 1969; Sucoff, 1975). Westing (1969) concluded that spring and summer
precipitation helped preserve the roadside vegetation by leaching salts through the soil
proﬁle. Others have speculated that deicing salts may accumulate in the soil due to
insufﬁcient precipitation (Davison, 1971; Pedersen et al., 2000), thus accumulating

within plant tissues (Button, 1964).

41

The purpose of this study was to assess whether deicing salts contribute to ﬂower

bud mortality to highbush blueberry growing adjacent to roads in western Michigan.

42

MATERIALS AND METHODS

Twelve blueberry ﬁelds in Ottawa and Muskegon Counties, Michigan, (Figure 1,
Table 3), were surveyed in May of 2002, 2003, and 2004 for ﬂower bud damage. Farms
were selected based on their proximity to roads that received deicing salts timing the
winter. Sampling locations were chosen at varying distances and orientations relative to
the road. At each sampling location, ﬁve twigs were selected ﬁom each of two adjacent
bushes (ten twigs were sampled at farms ‘1’ and ‘J’ in 2002), and the number of dead and
live ﬂower buds were recorded. Twigs were selected from the side of the plants nearest
the road. Assessments were during bloom, so that dead buds could be distinguished ﬁom
live buds. The GPS coordinates were determined for each sampling location with a
TSCI Datalogger (T rimble Navigation Limited, Sunnyvale, CA). Maps of each farm
were constructed by mapping the GPS data points on aerial photographic images on
Ottawa County using ArcView software version 3.2 (ESRI, Redlands, CA). The
relationship between bud mortality and distance to the road was determined by regression
analyses (TableCurveTM 2D, v. 2.00, San Rafael, Calif.) using pooled data (by year) ﬁ'om
farms adjacent to (including orientation) a speciﬁc road type; e.g., west of a divided
highway (farms ‘FG’, ‘H’), cast of a divided highway (‘A’, ‘I’, ‘J’, ‘L’), north of a 2-lane
highway (‘B’), south of a two-lane highway (‘C’), east of a secondary road (‘K’), and
north of a secondary road (‘D’, ‘E’).

To determine how salt deposition on twigs and injury to buds varied during the
winter, twigs were sampled at farms ‘C’ and ‘1’ in 2001, 2002 and 2003, and ﬁ'om farms

‘8’ and ‘K’ in 2003. At farm ‘B’, twigs were sampled from nine locations, three each at

43

25, 50 - 55, and 80 - 90 m from the road. At farm ‘C’, twigs were sampled from four
locations 35 - 50 m from the road, and from four locations, 85 - 105 m from the road.
Twigs from farm ‘1’ were sampled from eight locations, varying from 34 to 116 m ﬁ'om
the road. Twigs ﬁom farm ‘K’ were sampled from 9 locations 14, 27, and 57 m from the
road. Five samples at each location consisted of 15 cm long twigs from a single plant.
Twigs were selected from the side of the plant closest to the road.

Twigs were placed in plastic bags and on ice, transported to East Lansing, Mich.,
and shortened to 10 cm. The ﬁve twig samples were placed in 50 mL centrifuge tubes
containing 20 mL of double deionized water, capped, and inverted ten times to rinse off
surface salts. The rinsate was poured into separate tubes, and the electrical conductivity
was measured with an EC Meter (Orion Research, Boston, MA). EC reading was
multiplied by a conversion factor of 0.584 to determine salt concentration in tg‘cm'l (Soil
and Plant Analysis Council, 1992). Twigs were then wrapped in moist paper towels,
placed in another plastic bag, and held at 18 °C for 5 d, and dissected to determine the
number of dead and live ﬂower primordia. Mean ﬂower bud mortality was computed by
dividing the number of dead buds from all twigs sampled ﬁ'om each plant location by the
total number of ﬂower buds and multiplying this number times 100%.

Regression analyses were performed by road type because previous work has
shown that type of road can dramatically inﬂuence the degree of salt spray injury (Sucoff,
1975). Data for all farms east of a divided highway, those west of the divided highway,
thosenorth of a secondary road, and those east of a secondary road were combined.
(Farms ‘F’ and ‘G’ were combined, thus comprising one farm, ‘FG’.) The regression

models were selected that predicted mortality between 0 and 100% over the range of

44

distances measured at each farm, and highest R2 values, and those presented here were
considered the best of those generated. The regression models were generated by
TableCurveTM (San Rafael, CA), and the PROC NLIN command of SAS version 8.0

(Cary, NC) was used to estimated probability values for the chosen models.

45

 

0 10 20 Kilometers

Figure 1. Map of Ottawa and Muskegon County farms surveyed for ﬂower bud
mortality, May. 2002 — 2004.

46

 

Table 3: Location, number of observations, and surface
area of Michigan Blueberry farms surveyed for ﬂower bud
mortality in May.

Observations / farm

 

Orientation
relative to Area
adjacent surveyed

Farm roadway 2002 2003 2004 (ha)

 

A East ofUS 31 105 40 105 5.7
B North of M-45 94 6O 94 5.0
c South of M-45 133 29 133 5.5
D East of 144‘h 22 23 22 2.9
E West of144“‘ 19 19 19 0.4

FG West of US 31 13 22 13 0.5
H West ofUS 31 31 16 31 0.9
1 East ofUS 31 57 41 57 3.8
J EastofUS 31 21 21 21 0.5
K East of 120‘" 38 28 38 2.3
L East of I-96 68 22 68 6.2

 

47

RESULTS

Flower bud mortality in May: Flower bud mortality varied by year (Table 4). Overall
mortality levels were low in 2002 (mean of 9%), high in 2003 (41%) and intermediate in
2004 (24%). Generally, those farms with higher mean mortality had a higher range of
mortality across the farms (Table 4). Farms with the highest average mortality over all
three years were farm ‘J’ (45%), farm ‘L’ (39%), and farm ‘K’ (35%) whereas farms with

lower levels were farm ‘D’ (5%), and farms ‘B’ and ‘C’ each averaged 15%.

 

Table 4. Results of May farm surveys, 2002 — 2004, showing
mean and range of ﬂower bud mortality
Flower bud mortality (%)
2002 2003 2004
Farm Mean Range Mean Range Mean Rana

 

A 3 0-63 45 0-100 44 0-100
B 2 0-40 22 0-99 20 0-100
C 1 0-14 23 0-93 22 0-100
D 0 0-1 11 0-91 4 0-50

E 9 0-38 20 0-51 15 0-57

PG 0 0 35 2-100 25 0-67

H 3 0-6 29 0-92 16 0-100
I 22 0- 3 48 0-100 19 0-100
J 20 8-50 83 49- 100 31 49-94
K 4 0-29 64 8-100 36 8-100
L 11 0-66 72 22-100 33 22-100

 

Flower bud mortality levels are presented graphically for farm ‘H’, which was
west of a divided highway (Figures 5, 6, and 7), farm ‘1’, which was cast of the same
divided highway (Figures 8, 9, and 10), and farm ‘K’, which was cast of a secondary road

(Figures 11, 12, and 13). Although there was a great deal of mortality from year to year,

48

generally the greatest amount of injury was closest to the road(s). There was some
indication on farms ‘H’ and ‘I’ that mortality was also inﬂuenced by proximity to a
secondary road.

Regression Analyses. The relationship between proximity to the road and ﬂower
bud mortality were also examined by regression analysis, where data from farms adjacent
to a similar road type were combined, and regression models were chosen that best
described the relationships (Table 5). There were signiﬁcant relationships between
proximity to the road and bud mortality in 16 of 18 cases. All of the 16 signiﬁcant
models described decreasing mortality with increasing distance to the road. The farms
east of a divided highway (farms ‘A’, ‘I’, ‘J’, and ‘L’), south of a two-lane highway (farm
‘C’), and east of a secondary (farm ‘K’), had the strongest relationship between bud
mortality and proximity to the road.

The regression models and data for farms east of a divided highway, west of the
divided highway, and east of a secondary road are presented to show the relationships

more clearly (Figures 2, 3, and 4).

49

 

Table 5. Relationship between ﬂower bud mortality (y) and distance ﬁom road

(in meters) (x), on blueberry farms, by road type, 2002 — 2004.

 

 

Road type and orientation Function R2 P-val.z
East of divided highway (farms ‘A’, ‘I’, ‘J’, and ‘L’)

2002 y = 1.84 + 3091.9/xl'5 0.21 <0.0001

2003 y = 263 — 51.5 lnx 0.63 <0.0001

2004 y = 144 - 26.7 lnx 0.16 <0.0001
West of divided highway (farms ‘FG’, and ‘H’)

2002 y = 11 — 2.54 lnx 0.18 0.0038

2003 y = 51.2 — 0.000921” 0.14 0.0486

2004 y = 24.4 — 415.0/x'-5 0.07 0.0748
North of 2 lane highway (farm ‘8’)

2002 y = 2.18 — 0.015x 0.05 0.0284

2003 . y = -0.93 + 583614.5x'2'88 0.88 <0.0001

2004 y = 10.9 + 0.140x 0.04 0.0408
South of 2 lane highway (farm ‘C’)

2002 y = -1.13 + 7192/x2 0.48 <0.0001

2003 y = -16 + 1979/x 0.74 <0.0001

2004 y = 10.0 + 29139/x2 0.39 <0.0001
North of secondary road (farms ‘D’ and ‘E’)

2002 y =' 5.31 — 0.1 lx°-5 lnx 0.04 0.22

2003 y = 49.3 + 215/lnx 0.34 0.0001

2004 y = 45.2 — 10.7 lnx 0.25 0.0007
East of secondary road (farm ‘K’)

2002 y = 0.209 + 1039280x'4'57 0.47 <0.0001

2003 y = 104 — 0.03x2 0.81 <0.0001

2004 y = -297 + 1773 8.9/x2 0.77 <0.0001

 

ZProbability values estimated using PROC NLIN command in SAS.

50

Bud mortality (°/o)

 

 

80

H

8 8

N
a
l

 

   
 

Farms East of Divided Highway 2002

y = 1.84 + 3091.9/xl'5
R2= 0.21
P 5 0.0001

 

 

   
  

2003

y= 263 —51.5 lnx
R2=0.63
P 50.0001

 

 

100 r—r'

80

60~

 

 

 

 

2004

y=144-26.7 lnx
R2=0.16

P _<_ 0.0001

 

1 14 164
Distance from road (m)

214

Figure 2. Relationship between ﬂower bud mortality (y) and distance from
road (x) at farms ‘A’, I’, ‘J’, and ‘L’, in 2002, 2003, and 2004.

51

100

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Farms West of Divided Highway 2002
80 ~
60 -
_, y = 11 - 2.54 lnx
‘0 R2 = 0.18
P = 0.004
20.: _
I
o ‘ - '
100 . 7
F '. 2003
:g 8° "- ' . y=51.2—0.0009x2‘5
2- ' . R2 = 0.14
:35 60 r P = 0.05
1‘! .
O
E 40 ~
'0
3
20 .
100 - —-—————-
2004
80 l _
.' y = 24.4 — 415/x'-5
6° ‘ - R2 = 0.07 .
- P=007 I
40 _ l
I . .
20 i. F .
K .I I - . - i
0 T k 1 4 .1 W . a. T J
7 17 27 37 47 57 67 77

Distance from road (m)

Figure 3. Relationship between ﬂower bud mortality (y) and distance from
road (x) at farms ‘FG’, and ‘H’, in 2002, 2003, and 2004.

52

 

 

 

 

 

  
 

100
Farm East of Secondary Road 2002
so a
60 ~
y 2: 0.209 + 1039280x“-57
40 g R =0.47
P500001
20 ~
0 §____\__' , L
100
2003
33 80 l y=104-0.03x2
E 60 ~
g .
E 40 ~
'0
3
m 20 -

 

 

 

 

2004

y = -297 + 17738.9/rr2
R2 = 0.77
P 5 0.0001

 

 

 

 

44 54
Distance from road (m)

Figure 4. Relationship between ﬂower bud mortality (y) and distance from
road (x) at farm ‘K’, in 2002, 2003, and 2004.

53

Farm H

Secondary Road

 

['13 to o o o .1 or

2002

 

 

 

 

 

Key
ibhmedhkbdhmhway
I) almxo and
Scale (meters) up“ ndary
35 70 105
Flower Bud Mortﬂy’ (%)

 

0
1-19
20-39

40- 59

O
O
‘
60-79
80-100

 

 

 

Figure 5. Percent ﬂower bud mortality on farm ‘H’ in May 2002 illustrating ﬁeld

locations relative to the adjacent roads.

54

Secondary Road

 

OO O O

2003

 

z—>

 

Key
2-lane divided highway
U11 ved secondary road
Scale (meters) pa
H
35 70 105

Flower Bud Mortality 1%)

0
l- 19
20-39

0
O
O
. 40-59
60-79
80-100

 

 

   

 

 

 

Figure 6. Percent ﬂower bud mortality on farm ‘H’ in May 2003 illustrating ﬁeld
locations relative to the adjacent roads.

55

 

2004

z—>

 

 

Ke

 

 

Scale (meters)
H
35 70 105

O
O
;

   

 

 

1. ___.._.A4

y
2-lane divided highway
Unpaved secondary road

Flower Bud Mo '

0
1-19
20-39

40-59
60-79
80-100

%

 

Figure 7. Percent ﬂower bud mortality on farm ‘H’ in May 2004 illustrating ﬁeld

locations relative to the adjacent roads.

56

 

Farm 1

 

 

 

 

2 lane divided highway

 

 

z—>

Paved secondary road
ye (mag)
23 46 69 Flower Bud Mortality 1%),
0 0
0 I - I9
20 -- 39

 

40-59
60-79

 

80-100

 

 

 

Figure 8. Percent ﬂower bud mortality on farm ‘1’ in May 2002 illustrating ﬁeld
locations relative to the adjacent roads.

57

Farm I

 

 

 

 

2 lane divided highway
Paved secondary road

 

 

M
23 46 69 Flower Bgd Moﬂy’ (2.)

0 0
. 1—19
20—39

40-59
60—79

Z—>

80-100

 

 

 

 

Figure 9. Percent ﬂower bud mortality on farm ‘1’ in May 2003 illustrating ﬁeld
locations relative to the adjacent roads.

58

Farm 1

Secondary Road

 

 

2 lane divided highway
Paved secondary road .

 

Scale (meters:
23 46 69 Flower Bud Mortality 1%)

z—>

 

 

 

Figure 10. Percent ﬂower bud mortality on farm ‘l’ in May 2004 illustrating ﬁeld
locations relative to the adjacent roads.

59

Farm K

 

 

 

O O o
o o o
o
o o
. t
0 o N
o o o
g: o o o
'93
E o o o
g Key
D.
0 o 0 —— Unpaved secondary road
Scale (meters)
0 o o 2
o o 0 Flower bud mortality (%)
° 0
o o 1 — 19
o 0 20 - 39
O 40 — 59
' ° ° . 60 - 79
O O o . 80 — 100

 

 

Figure 11. Percent ﬂower bud mortality on farm ‘K’ in May 2002 illustrating ﬁeld
locations relative to the adjacent road.

60

 

 

 

O

U]

0

O

o

a

o.
3

H

o

9

o.

O

 

 

.0 °
l

Farm K

 

Key
Unpaved secondary road

Scale (meters)

Flower bud mortality (%)
o 0

l—19
20—39
40—59

.
C
O
. 60—79

. 80—100

 

 

 

Figure 12. Percent ﬂower bud mortality on farm ‘K’ in May 2003 illustrating ﬁeld

locations relative to the adjacent road.

61

 

1 Farm K

 

0
O

 

 

 

. O
O
O o t
g N
O o
O 0 °
'4 0 ° °
§
3 O '- °
i“ O K...
. O
———-Unpavedsecondaryroad
Scale meters)
0 o o aria-
. o ’
Flowerbudmortality(%)
O O 0
e - -
0 20—39
. o o C 40-59
60—79
0 ' ° .
‘ . 80-100

 

 

Figure 13. Percent ﬂower bud mortality on farm ‘K’ in May 2004 illustrating ﬁeld
locations relative to the adjacent road.

62

 

Dormant twig sampling. Flower bud mortality and salt deposition levels were
recorded monthly ﬁom four farms. In 2003, bud mortality increased through the winter
on plants closest to the two-lane highway at farm ‘B’, but that trend was not observed on
plants ﬁrrther away from the road (Figure 14A). Salt deposition on dormant shoots was
dynamic, but the greatest amount of salts rinsed from the shoots were from plants closest
to the two-lane highway (Figure 14B).

Bud mortality increased generally through the winter at farm ‘C’, and was always
greater on plants closest to the two-lane highway (Figure 15A). Two general distances to
the road were used for comparison at this farm (‘close’ and ‘far’), encompassing a narrow
range of actual distances (35 — 50 and 85 - 105 m, respectively). Salt deposition levels
also varied with distance to the road, and shoots sampled from plants closer to M-45
always had higher more salt deposited on the plants (Figure ISB), which conforms to
expectations. But as in the case of farm ‘B’ (due north of this farm), salt deposition
levels were dynamic and not additive through the winter.

Bud mortality levels at farm ‘1’ always increased through the winter (Figure 16A).
Salt deposition levels were dynamic, as seen at the other farms, but the highest salt
deposition level (38 rg'cm'l twig tissue) was measured from shoots from this farm
(Figure 16B). Mean bud mortality and salt deposition were averaged across the whole
farm, as the orientation of this farm to US 31 made it difﬁcult to sample twigs at different
distances to this divided highway.

Plants at farm ‘K’ were evaluated only in 2003 for ﬂower bud injury and salt
residues at different distances to the nearest road (Figure 17). Bud mortality was initially

high on plants closest to the road, and increased to 100% in Feb. and Mar. (Figure 17A).

63

Plants at further distances to the road always sustained less bud injury than the closest
plants, but always increased in mortality through the winter. Salt deposition was always
greatest on shoots collected closest to the road, but did not seem to accumulate through
the sampling period. Lesser amounts of salts were deposited on plants further ﬁom the

road, with salt levels that seemed to remain constant through the winter (Figure 17B).

Flower bud mortality (%)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I25m
ISO-55m
E180-90m
January February March

50

451 B,

4OJ I25m

35 n u50-55m
DBO-QOm

 

 

 

 

Salt deposltlon (ug'cm'1 twig tissue)

 

 

 

 

 

February

Sampling time
Figure 14: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at farm

‘B’, Ottawa County, Mich., 2003. Bars represent standard error. Legend indicates
distance to road.

65

 

88

I35- 50m

1385- 105m
20 —
10 -
o -

January February March January March January February March
2001 2002 2003

Itlt(%)
8838

Flower bud mortal
to :5
O O

 

 

 

B. F3150...

12185-105m

 

Salt deposltlon (ug‘cm'1 twig tissue)

January March January February March
2002 2003
Sampling time

Figure 15: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at farm
‘C’, Ottawa County, Mich, 2001 - 2003. Bars represent standard error. Legend

indicates distance to road.

66

Flower bud mortality (%)
88 ‘6’ $39 80
IL- ____-_ L L L-

0 t7
January mFebruary March January March January Febnlary March

2001 2002 2003

O
3104:
559 I 1

January January February March

2002 mp.“ m 2003

Figure 16: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at farm
‘1’, Ottawa County, Mich, 2001 - 2003. Bars represent standard error.

67

Flower bud mortality (%)

10‘

 

#LL—LTI .7

January

 

 

I14m
I27m
30 3 057m

 

 

 

Salt deposition (ug'cm" twig tissue)

 

 

January February
Sampling time

Figure 17: Percent ﬂower bud mortality (A) and salt deposition (B), by month, at farm
‘K’, Ottawa County, Mich, 2003. Bars represent standard error. Legend indicates
distance to road.

DISCUSSION

These ﬁeld observations indicate that deicing salts are responsible for much of the
injury in blueberry ﬁelds next to Michigan roads. This conclusion is based on general
patterns of mortality within ﬁelds as well as salt levels measured on twig tissue. Deicing
salt has been shown to damage lowbush blueberries in Nova Scotia (Eaton et al., 1999),
as well as other woody roadside plants (Hofstra and Hall, 1970; Sucoff, 1975; Lumis et
al., 1976; Thompson and Rudder, 1986; Pedersen et al., 2000; Bryson and Barker, 2002).

While wind direction was not monitored as part of these studies, general
observations are that prevailing winds move eastward in this region. Patterns of injury in
farms were generally consistent with expected movement of salts off of roads. For
example, the injury on farms east or downwind of a divided highway consistently were
greatest closest to the road (Figures 2, and 11 — 13), whereas there was no consistent
pattern of injury on farms west of the highway (Figures 3, and 8 - 10). Farms ‘H’, ‘I’, ‘J’
also bordered secondary roads, which may have contributed to mortality, since there was
higher mortality along secondary roads (Figure 5 — 10). Salt injury to plants is usually
greater downwind of roads (MDOT, 1993). Similar patterns of injury were observed at
Farm ‘K’, which is situated east (downwind) of a secondary road. Injury was
consistently higher closest to the road (Figures 11 — l3).

Farms north 0r south of salted roads showed clear mortality patterns some years
but not others. Injury on farm ‘C’, which is south of a two-lane highway, was
consistently highest close to the road (Table 5). In contrast, farms that were north of the
same highway (farm ‘B’), and north of a secondary road (farms ‘D’, ‘E’), showed similar

patterns in one season, but inconsistent patterns in two other seasons (I able 5). Although

69

prevailing wind direction is generally from the west, winds out of the northwest or
southwest would have different effects on salt deposition levels on farms north or south
of the two-lane highway.

Trafﬁc volume and salting rates can inﬂuence damage to roadside vegetation
(Sucoff, 1975). Farms with low levels of bud mortality were usually west of the divided
highway (farms ‘FG’, and ‘H’), and north and south of the two-lane highway (farms ‘8’,
‘C’, respectively), and north of the secondary road (farms ‘D’ and ‘E’). Deicing
application rates for Ottawa County were not available, so it is not possible to make
comparisons of salt application by road type. Hence, it is not known if the low bud
mortality incuned by farms ‘D’ and ‘E’ were a result of less salt being applied to these
types of roads, lower ADT, prevailing wind direction, or a combination of all factors.
Average daily traffic data for Ottawa County were provided by Michigan Department of
Transportation, and from this it is clear that ADT was higher on the divided highway than
on the other road types (data not shown).

Some surveyed farms were bordered by more than one road (Figures 5 — 10),
affecting the pattern of bud injury. For example, farm ‘1’ was bordered by US 31 to the
west, and a secondary road to the south (Figures 8 - 10). It appears that plants close to
either road sustain more bud injury. Bud mortality at farm ‘H’ was somewhat evenly
distributed throughout the ﬁeld, but also found along the secondary road to the north
(Figure 5). The secondary road to the north of farm ‘H’ also appeared to contribute to
injury (Figures 5 — 7).

Roadside trees and shrubs may shield plants ﬁom salt spray and affect ﬂower bud

injury and salt deposition levels (Eaton et al., 2004) (Appendices 14 — 22) Although

70

some farms in this survey had varying amounts of vegetation borders, there was no clear
indication that this affected pattemsof injury on these farms. In virtually all cases.
vegetation consists of mixed deciduous and coniferous species at varying heights.

Flower bud mortality on four farms was monitored monthly, and tended to
increase during the course of the winter. Mortality was apparent early in the winter on
plants closest to the road, and increased with time (Figures 14A, 15A, 17A). Mortality
on plants furthest from the road tended to be minimal early in the winter, and did not
always increase with time (Figures 14A, 15A, 17A). This suggests that injury associated
with salt is cumulative, and not related to a single weather event. For example, injury on
plants close to the road at farms ‘B’ and ‘K’ increased as the season progressed in 2003
(Figures 14A and 17A), whereas injury to plants farther from the road did not always
increase through the winter.

Salt levels on twigs were usually highest close to the road (Figure 14A, 15A,
17A). Salt levels did not consistently increase or decrease from month to month. At
some farms, salt levels seemed to increase (Figure 17B), at other farms salt levels seemed
to decrease (Figure 16B). Variability of salt levels on twigs could be the result of
precipitation events. However, winter precipitation can occur as rain or snow, and rain
would be expected to remove more salt than snow.

. Salt levels in this survey were derived from electrical conductivity and ranged
from 1 to 39 rg‘cm" shoot tissue. It is not known whether all of this salt was derived
from road salt since Na and Cl were not speciﬁcally measured. Eaton et al. (1999)
reported a linear decrease in NaCl residues on lowbush blueberry twigs ﬁ'om a salted

highway by analyzing for chloride speciﬁcally.

71

Deicing salt was more damaging to ﬂower buds during colder winters. Bud injury
was greatest in 2003 and 2004 than in 2002 (Table 4). The 2001 — 2002 winter was
relatively mild, with temperatures falling below —15 °C only once (Appendix 3).

Average bud mortality the following May was low (Table 4). Temperatures fell below
—1 5 °C 5 times during the 2002 — 2003 winter, (Appendix 5), and below —20 °C three
times during the 2003 — 2004 winter (Appendix 7). Flower bud mortality levels were
considerably higher after the cold 2002 - 2003 and 2003 — 2004 winters, averaging 41%
in 2003 and 24% in 2004. Salt has been shown to reduce the cold hardiness of plants
(Sucoff, 1975; Sucoff et al., 1976; Sucoff et al., 1976A).

Sucoff et al. (1976, 1976a) showed that NaCl sprays decreased the cold hardiness
of the species tested, although the mechanism of injury remained elusive. Exposing
blueberry ﬂower buds to deicing salt spray may cause injury by disabling the cold
tolerance mechanism within the ﬂower buds, but this needs to be ﬁllly investigated. That
deicing salts deposited onto dormant blueberry twigs are somehow affecting water
relations within the ﬂower buds should also be investigated, as water content of blueberry
ﬂower buds is associated with cold tolerance (Bittenbender and Howell, 1975). Flower
buds are recognized as critically sensitive to freeze injury (Bittenbender and Howell,
1976), and may be more susceptible than shoots to cold injury, as they lose heat readily
due to a lower heat capacity and more surface area than shoots (Andrews et al., 1986). It
is possible that several mechanisms resulting in ﬂower primordia death begin occuning
simultaneously soon after exposure to salts in general.

Throughout the course of these farm surveys, it was apparent that deicing salt

injury symptoms (e.g., shoot dieback, ﬂower bud mortality) resemble ‘classic’ winter

72

injury symptoms. These symptoms are even more extreme after severe winters. The
difference between these two types of injury are the relationship with distance to the
road; i.e., winter injury can usually be expected to uniformly affect any given ﬁeld, but
especially low-lying areas due to the lack of cold air drainage, but deicing salt spray
usually only affects vegetation adjacent to treated roads.

Long-tenn exposure to deicing salt spray may result in severe plant stress. Plants
in the southern part of farm ‘A’ nearest to US 31 (Appendix 14) were apparently severely
stressed, and several had been pruned to the ground just prior to the 2004 farm survey.
One additional observation during 2003 and 2004 was that many plants in the rows
closest to US 31 at farms ‘A’ and ‘I’ had severe dieback and appeared near death, with
these plants all showing signs of possible saprophytic ftulgal pathogen infections. This
was diagnosed by the presence of necrotic regions directly surrounding vegetative and
ﬂoral buds on shoots; bleached-white cankers on shoots and canes; and the presence of
pycnidia on last year’s shoot growth. It is possible that salt spray stress may offer certain
pathogenic fungi an entry court into the necrotic tissues, thus further weakening the
plants (Shaw et al., 1982).

Deicing salts appear to have been responsible for ﬂower bud injury and twig
dieback in blueberry ﬁelds adjacent to Michigan highways. This conclusion is based on
the following observations: 1.) Patterns of bud injury are consistent with proximity to
roads and prevailing wind direction; 2.) Elevated salt levels are apparent on twigs closest
to salted roads; 3.) Deicing salts have been shown to injure lowbush blueberries and

other woody plants.

73

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Bittenbender, HO and G.S. Howell. 1975. Interactions of temperature and moisture
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Bittenbender, HO and G.S. Howell. 1976. Cold hardiness of ﬂower buds from selected
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Gibbs, J .N. and DA. Burdekin. 1983. De-icing salt and crown damage to London plane.
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Northover, J. 1987. NaCl injury to dormant roadside peach trees and its effect on the
incidence of infections by Leucostoma spp. Phytopathology 77:83 5-840.

Pedersen, L.B., T.B. Randrup and M. Ingerslev. 2000. Effects of road distance and
protective measures on deicing NaCl deposition and soil solution chemistry in planted

75

median strips. J. Arbor. 26:238-244.

Shaw, L.J., E.E. Griffiths, M.J. Hodson and SJ. Wainwright. 1982. The effect of salt
drunping on roadside trees. 11. Arbor. J. 6:241-249.

Simini, M. and LA. Leone. 1986. Studies on the effects of de-icing salts on roadside
trees. Arbor. J. 10:221-231.

Soil and Plant Analysis Council, Inc. 1992. Handbook on reference methods for soil
analysis. Pp. 162 — 166. Georgia: Georgia University Station.

Sucoff, E. 1975. Effect of deicing salts on woody vegetation along Minnesota roads.
Investigation #636, Minn. Ag. Exp. Sta. Tech. Bull.

Sucoff, E., S.G. Hong and A. Wood. 1976. NaCl and twig dieback along highways and
cold hardiness of highway versus garden twigs. Can. J. Bot 54:2268-2274.

Sucoff, E., and S.G. Hong. 1976a. Effects of NaCl on cold-hardiness of Malus spp. and
Syringa vulgaris. Can. J. Bot. 54:2816-2819.

Thompson, J .R., A.J. Rutter and RS. Ridout. 1986. The salinity of motorway soils 1.

Variation in time and between regions in the salinity of soils on central reserves. J. Appl.
Ecol. 23:251-267.

Thompson, J .R and A.J. Rutter. 1986. The Salinity of Motorway Soils. IV. Effects of
sodium chloride on some native British shrub species, and the possibility of establishing
shrubs on the central reserves of motorways. J. Appl. Ecol. 23:299-315.

Walton, G.S. 1969. Phytotoxicity of NaCl and CaC12 to Norway maples.
Phytopathology 59:1412-1415.

Westing, AH. 1969. Plants and salt in the roadside environment. Phytopath. 5921174-
1181.

76

CHAPTER III

DEICING SALTS REDUCE COLD HARDINESS AND INCREASE

FLOWER BUD MORTALITY OF HIGHBUSH BLUEBERRY

77

ABSTRACT

DEICING SALTS REDUCE COLD HARDINESS AND INCREASE FLOWER BUD

MORTALITY OF HIGHBUSH BLUEBERRY (Vaccinium corymbosum L.)

Injury to highbush blueberries growing along major and minor roads in Ottawa
County, Mich, has been observed since the early to mid-19903. Symptoms include shoot
dieback, reduced ﬂowering and yields. To determine if this injury was the result of
deicing salts applied to roads, salt (NaCl) Spray was applied to potted blueberry plants,
and to the plant root zones. Bushes sprayed 6 times during the winter with NaCl
solutions (0, 2, 4, 8, 16 and 32 g‘L") developed the same injury symptoms observed in
roadside ﬁelds, and injury severity was proportional to the concentration applied. The
root media of other potted plants was saturated with NaCl solutions (0, l, 3, 9 and
27 g'L") in Mar. 2002. Pots were then rinsed with fresh well water when growth began
in April to determine if soil salt caused similar damage. The highest soil salt levels killed
most above ground growth, and damage diminished with decreasing salt levels. Twigs
were also excised from branches sprayed twice with NaCl solutions or water and frozen
incrementally to measure the temperature resulting in 50% ﬂower bud mortality (LTso).
Salt exposure reduced the LTso of ﬂower buds, by as much as 11.0 °C, relative to the

control, even within 7 hours of treatment. Additional studies with chloride salts (NaCl,

78

KCl, CaC12, MgClz) and sodium salts (NaCl, NaAC, Na2S04) indicated that most salts

reduced the cold tolerance of bluebeny ﬂower buds to some degree.

79

INTRODUCTION

Sodium chloride is the most widely used deicing material applied to roads in the
north central and Eastern United States (MDOT, 1993). Unfortunately, salt damages
deciduous and coniferous vegetation growing along treated roads (Lumis et al., 1975;
Bowers and Hesterberg, 1976; MDOT, 1993; Bryson and Barker, 2002). Symptoms
include shoot/branch dieback, browning of evergreen needles in late winter/early spring,
reduced ﬂowering, delayed foliar growth, witch’s broom growth (branch ends), early fall
coloration, and plant death in extreme cases (Sucoff, 1975). Species vary (within and
between) in sensitivity to aerial salt spray deposited directly on plants and soil salt
inundation resulting from melt water runoff (Bryson and Barker, 2002).

Highbush bluebeny plantings along salted roads in western Michigan commonly
exhibit twig dieback and ﬂower bud mortality. The degree of injury is inﬂuenced by
distance to the nearest salted road, orientation of the farm to the nearest salted road (in
this instance, east or west of a divided highway, or north or south of a two-lane highway),
and severity of the winter (Chapter 2). Flower mortality and salt deposition on twigs
decreased with distance from the road, and generally increased as the winter progressed.
However, although no work on highbush bluebeny had been done, some work describing
the effects of deicing salt on yield and ﬂowering in lowbush blueberry (Vaccinium
angustifolium) was performed in Nova Scotia in the late 19903 (Baton et al., 1999).

Most of the studies dealing with deicing salt damage to woody plants focused on
the phytotoxicity of NaCl. However, various chemicals other than NaCl are used for
deicing purposes. The phytotoxicity of some of these alternative deicing materials (e.g.,

MgClz, KCI, CaC12, Na+-acetate) is not known. Exposure to NaCl decreases the cold

80

hardiness of certain woody species (Sucoff, 1975; Sucoff and Hong, 1976; Sucoff and
Hong, 1976a; MDOT, 1993).

How NaCl decreases the cold tolerance of susceptible species is unknoWn. Salt
residues on tissue surfaces may cause injury by desiccating cells (Sucoff, 1975). Salt
may also penetrate tissues and disrupt cellular membranes (Zobel and Nighswander,
1990). Sucoff (1975) proposed salt enters dormant shoots via leaf traces.

The objectives of this research were to determine if the injury symptoms observed
on roadside blueberries could be induced by spraying young plants, or treating soil with

NaCl, and determine how NaCl and other salts affect the cold tolerance of blueberry.

81

MATERIALS AND METHODS

Salt Spray Simulation. Thirty two-gallon ‘Bluecrop’ blueberry plants approximately
ﬁve years-old and one meter tall were heeled into the ground in Dec. 2001 in a lathouse
in East Lansing, Mich. Plants were sprayed to run-off on 7 Jan. 2002 with NaCl
solutions of 0, 2, 4, 8, 16, or 32 g'L'l using a backpack sprayer. Statistical design was a
completely randomized design, with ﬁve whole plant replicates per treatment.
Aluminmn foil was placed around the base of pots to prevent solutions from entering the
soil. A screen was used to shield adjacent plants. Sprays were repeated ﬁve times at
two-week intervals thereafter.

Salt deposition on twig surfaces was measured before each application by
collecting one twig from each plant and placing twigs in 50 mL centrifuge tubes
containing 20 mL of double deionized water. Tubes were capped and inverted ten times
to rinse off surface salts. The electrical conductivity of the rinsate was measured with an
EC Meter (Orion Research Boston, MA). The linear length of twigs was measured and
salt deposition was expressed per unit of twig length. When plants reached full bloom
(20 May), the numbers of live and dead ﬂower buds were counted on ﬁve randomly
sampled twigs per bush. Data were analyzed using the PROC GLM command (SAS
Institute, Cary, NC), and linear and quadratic regression analyses were performed using
MINITAB (Release 13.2, State College, PA).

Soil Salt Inundation. In Dec. 2001, 25 ‘Jersey’ blueberry plants in one-gallon
containers were heeled into the ground in a lathouse so that the tops of the pots were 5 cm
above the soil. Plants were arranged in a completely randomized design, and ﬁve

replicate plants were treated with 1 liter of NaCl solutions of 0, 1, 3, 9, or 27 g‘L'l on 1

82

Mar. 2002. Solutions were poured into the pots so that they percolated throughout the
media. Four weeks later, at bud swell, each pot was ﬂushed with approximately 4 L of
water. Plants were kept in the lathouse until one month after full bloom (June 20), when
new shoot growth, leaves, ﬂowers and fruit were removed ﬁom each plant. Tissues were
dried at 70 °C for 10 d and weighed. Dried tissue samples were analyzed for Na”
(Thomas, 1982) and Cl’ (Hipp and Langdale, 1971) by the MSU Soil and Plant Nutrient
laboratory. Data were subjected to AN OVA using the PROC GLM command (SAS
Institute, Cary, NC), and linear and quadratic regression analyses were performed using
MINITAB (Release 13.2, State College, PA).

Cold Hardiness Study 1. To study the effect of salt spray on the hardiness of blueberry
ﬂower buds, ﬁve branches from mature ‘Jersey’ bushes in East Lansing, Mich. were
sprayed to nmoff with NaCl solutions of O (deionized water), 16, or 64 g'L'l on 21 and 22
Dec. 2002. On 23 Dec. 2002, ﬁfteen twigs at least 10 cm long and possessing three or
more ﬂower buds were removed from each branch. Twigs from the ﬁve branches
sprayed with the same salt treatment were combined in a plastic bag containing a moist
paper towel, and transported in an ice-ﬁlled cooler to the laboratory.

Within 24 hours, the twigs were prepared for controlled temperature ﬁeezing as
described previously (Howell and Weiser, 1970; Stergios and Howell, 1973). Three
twigs from each salt treatment were bundled together in moist cotton cheese cloth
wrapped in aluminum foil. Bundles were placed in an Ultralow Freezer (Scientemp,
Adrian, Mich.) programmed to cool at a rate of 3 °C per hour. Three bundles were placed

in a cold room at 3 °C, to serve as a control.

83

Three bundles (replicates) were removed when the temperature reached -l7, -20, -23, -26,
-29, and -32 °C. Bundles were held at 3 °C for I d, and 20 °C and 100% relative
humidity for 5 d. Buds were cross-sectioned and observed for oxidative browning using
a dissecting microscope to assess ﬂower bud viability. Brown primordia were rated as
dead. The temperature resulting in approximately 50% ﬂower primordia mortality (LTso)
was calculated using the modiﬁed Spearmann-Karber method (Bittenbender and Howell,
1974). LTso = T. — (1/2 d) + (1 (sum bi) / n, where LTso = temperature at which 50% of
samples are killed; T. = highest lethal temperature; d = temperature interval between
treatments; bi = total number of dead samples in the 1'” treatment; and n = number of
samples per treatment. Linear regression analyses were performed on LTso values using
MINITAB (Release 13.2, State College, PA).

Cold Hardiness Study 2. To determine the effects of road salt exposure on hardiness of
bluebeny ﬂower buds, 10 cm twigs bearing at least three contiguous ﬂower buds were
excised on 13 Feb. 2003 from mature ‘Bluecrop’ plants ﬁom a farm in Ottawa County,
Mich. This farm was cast of a major divided highway, and had experienced high levels
of ﬂower bud mortality. Sampled plants were approximately 65 m and 200 m ﬁ'om the
highway, and twigs were placed in plastic bags, and transported back to East Lansing,
Mich, in an ice-ﬁlled cooler for ﬁecze-testing as described previously. Bundles
containing 3 twigs from each ﬁeld position were removed at 3 °C/hour temperature
intervals from -18 °C to -33 °C. The statistical model used was a split-split-plot design,
with the bundle forming the main plot, twig was a sub-plot, and bud position the sub-sub-

plots. Data were analyzed for AN OVA using the PROC GLM command (SAS Institute,

84

Cary, NC), and linear and quadratic regression analyses were performed using MINITAB
(Release 13.2, State College, PA).

Cold Hardiness Study 3. To study the effects of lower spray concentrations of NaCl on
cold hardiness, branches of 20 year-old ‘Bluecrop’ plants at a small commercial
blueberry ﬁeld in Haslett, Mich. were treated with 0, 4, 8, or 16 g'L‘l on 27 and 28 Feb.
2003. Twigs were excised on 1 Mar. 2003, placed in plastic bags in an ice-ﬁlled cooler,
and returned to the laboratory for controlled freezing. Twigs were prepared, frozen, and
evaluated as described previously, but for this study, three bundle replicates were
removed when temperatures reached -15, -18, -21, -24, -27, -30, and -33 °C.

Cold Hardiness Study 4. The goal of this study was to determine how rapidly NaCl
exposure affects the cold hardiness of blueberry ﬂower buds. Branches of mature
‘Jersey’ blueberry plants in East Lansing, Mich. were sprayed to run-off with NaCl at O
or 64 g'L'l on 13 Jan. 2004. Treated branches bore a minimum of 15 twigs, 10 cm long,
and three contiguous ﬂower buds. Twigs were excised 1 hour after treatment, transported
back to Michigan State University in plastic bags, and prepared within 7 h for cold
hardiness studies. For this test, three bundle replicates were removed every two hours, at
2 °C/hour decrements between -17 °C and -29 °C. Post-freezing handling and evaluation
of ﬂower primordia were the same as described previously. Statistical methods were the
same as in Study 3.

Cold Hardiness Study 5. This study compared the effects of four Cl' salts on the cold
hardiness of blueberry ﬂower buds. On 12 and 13 Jan. 2004, branches of mature ‘Jersey’
blueberry plants were sprayed with deionized water, or solutions of potassium chloride

(KCl), magnesium chloride (MgClz), NaCl, and calcium chloride (CaC12). All solutions

85

contained the same Cl' concentration as that in NaCl at 64 g'L", 0.6M Cl', and were
applied by a hand Sprayer to drip. Four bundle replicates were removed every hour at 3
°C decrements, from -16 °C to -31 °C. Post-freezing handling and evaluation of ﬂower
primordia were handled as in the previous cold hardiness studies.

Cold Hardiness Study 6. This study tested the effects of Na+ salts on the cold hardiness
of blueberry ﬂower buds. On 15 and 16 Jan. 2004, branches of 12 year-old ‘Jersey’
blueberry plants were sprayed with deionized water, or solutions of sodium sulfate ‘
(Na2S04), NaCl, or sodium acetate (NaAC). Solutions were standardized to the same
Na+ concentration as that in NaCl at 64 g'L", 0.39M Na+, and applied by a hand sprayer
to drip. Three bundle replicates were removed every hour, at 3 °C decrements between -
16 °C to -31 °C. Post-freezing handling and evaluation of ﬂower primordia were handled

as in previous studies.

86

RESULTS
Salt Spray Study . Flower bud mortality increased linearly with increasing NaCl spray
concentration (Figure 15), from 2% (control) to 48% (32 g'L'l NaCl). Spraying branches
over 7 weeks showed salt deposition levels from 3.1 to 4.1 lg'cm'l NaCl after the ﬁrst
spray, and deposition levels were lower after the ﬁnal Spray application on 19 Mar. 2002
than after the ﬁrst spray application (Figure 16). Highest NaCl treatment (32 g’L'l NaCl)
always had higher amounts of NaCl deposited on the twigs, but the lower levels did not
always have the lowest levels. Salt rinsed from sprayed twigs ranged ﬁem 2.8 to 4.1
lg'cm'l stem length. Treatments did not signiﬁcantly affect salt residues until the later

sampling dates, when the higher spray concentrations resulted in higher salt residues.

 

  
  

Dead ﬂower buds (%)
8 8 8

 

 

y I 1.451: + 2.15
R’ a 0.88
P < 0.0001
10
o 7 I I I T T T
0 5 10 15 20 25 30 35

Sprayed NaCI (g'L")

Figure 18: Percent dead ﬂower buds of ‘Bluecrop’ blueberry bushes treated with NaCl
sprays on 19 Jan., 4 Feb., 18 Feb., 1 Mar., and 19 Mar. 2002, in May 2002.

87

 

 

 

4 .
' a
\ .0...
\ .o \

 

 

 

 

 

 

 

 

 

 

.9
E
's
p
0 4
g A 3 A .‘\, ' ,ﬁ—“e. \\ ab
a. g : "> ./ ',-"' ‘~. .....
3 a . '.v,’,’ -- .....
c g 5 \V '
o 2 - —e—09 NaCl/L c
'a - c
"2 i ‘1' 33
e ,1 ....... l
2- ’ i +169 l
a 4! +329 J
0 L I I *‘ I T
1l19l02 2l2/02 2/16/02 3/2/02 3l16/02
Sampling date

Figure 19: Salt rinsed ﬁ'om twig surfaces of dormant ‘Bluecrop’ highbush blueberry
branches treated with NaCl sprays on 19 Jan., 4 Feb., 18 Feb., 1 Mar., and 19 Mar. 2002.

Letters indicated signiﬁcant differences between treatment means (P S 0.05). No letters
indicated insigniﬁcant differences.

88

Soil Salt Inundation. Increasing salt levels applied to soil in March resulted in a linear
increase in ﬂower bud mortality by May (Figure 17), and a decrease in dry matter
production by June (I able 12). Plants treated with the higher salt levels contained a
considerable amount of dead branches, and vegetative buds were either killed or
developed slowly. Even though the soil volume was leached with water in April, soil

Na+ and Cl' levels in May increased linearly with application rate (I able 12).

 

Table 5: Soil N? and Cl' concentrations and new dry matter production
(leaves, shoots, fruit) by 20 June 2002 of potted ‘Bluecrop’ blueberry plants
treated with NaCl solutions applied to the rootzone on 1 Mar. 2002.

 

 

 

Leaf, shoot and Soil salt (mg‘kg'l)
NaCl applied fruit dry weight
(8L. ) (g) Na Cl
0 11.0 95 270
1 1 1.9 404 481
3 11.4 777 801
9 8.7 1810 1970
27 1.3 2602 2990
Signiﬁcance
Linear u t t :1: :1 as a
Quadratic I I I I I I I I I

 

*** Signiﬁcant main effects at P 5 0.0001, for NaCl treatments partitioned into
linear or quadratic orthogonal contrasts.

89

 

  
 

 

 

 

35 80-
E 705 y=2.99x+18.4
1: 605 R’=o.ee
E so- P<0.0001
E405
'3 30—
3 4
2 201
"' 10-« o

o r I I I r I r a r

0 3 6 9 12 15 18 21 24 27 30

Soil applied NaCl (91")

Figure 20: Relationship between rate of NaCl applied to soil in March and ﬂower bud
mortality in potted ‘Jersey’ blueberry bushes in May 2002.

Cold Hardiness Study 1. NaCl sprays applied to ‘Jersey’ branches for two consecutive
days in January resulted in a linear reduction in ﬂower bud hardiness (Table 13). Sprays
of 16 and 64 g-L" NaCl reduced the LT... of buds by 7.5 °c and 11.0 °C, respectively,

compared to controls.

 

Table 13: Effect of NaCl sprays applied to branches of ‘Bluecrop’
highbush blueberry on 21 and 22 Dec. 2002, on cold hardiness of
ﬂower buds measured on 2 Jan. 2003.

 

 

NaCl applied
SEL‘ ) LTso (0 C)
0 -28.0
16 -20.5
64 -l7.0
Signiﬁcance 2
Linear *"‘ "‘

 

*** signiﬁcant linear response, P g 0.001.

 

Cold Hardiness Study 2. Flower buds sampled in Feb. from bushes 65 m ﬁ'om a major
divided highway in West Mich. were signiﬁcantly (P 5 0.0001) less hardy (LTso = -13.0
°C) than buds ﬁ'om bushes 200 m from the highway (LTso = -31.0 0C).

Cold Hardiness Study 3. ‘Bluecrop’ branches sprayed for 2 consecutive days in
February with NaCl ranging ﬁnal 0 to 16 g-L" also exhibited a linear decrease in ﬂower
bud cold hardiness measured 5 days later (Table 14). The highest NaCl concentration

reduced the LTso by 6.0 °C, compared to the control.

 

Table 14: Cold hardiness of ﬂower buds measured on
9 Mar. 2003 treated with NaCl sprays applied to
branches of ‘Bluecmp’ highbush blueberry on 27 and

 

 

28 Feb. 2003.
NaCl applied (g-L") LTso (°C)
0 -225
4 -18.0
8 -19.5
16 -16.5
Signiﬁcance
Linear I I I
Quadratic 1'"

 

*** sigpiﬁcant at P 5 0.001.

 

Cold Hardiness Study 4. ‘Jersey’ branches sprayed with NaCl at 64 g‘L'l, then sampled
an hour later and tested for hardiness within 7 h also had a signiﬁcantly (P = 0.012) lower
ﬂower bud hardiness (LTso = -24.0 0C) than control (LTso = -28.5 °C).

Cold Hardiness Study 5. Sprays of chloride salt solutions (NaCl, CaC12, MgCIz, KCl)

supplying equivalent Cl' concentrations all reduced the hardiness of ‘Jersey’ ﬂower buds

91

(Table 15). Potassium chloride resulted in the smallest reduction in cold hardiness

(5.0 0C).

 

Table 15. Cold hardiness of ﬂower buds measured on 21
Jan., 2004 treated with Cl' salt solutions applied to branches
of ‘JerseLhighbush blueberry on 13 and 14 Jan. 2004.

 

 

 

Treatment LTso (°C)
Control -26.Oaz
KCl -21.5b
MgClz -18.0c
CaC12 -l7.50
NaCl -l6.0c

P-value _<_ 0.0001

 

2 means within columns followed by a different letter are
iigniﬁcantly different bLTukey’s HSD (P S 0.05).

 

Cold Hardiness Study 6. Spraying ‘Jersey’ branches for two consecutive days in

January with NaCI, NaAC, Na2804 (supplying equivalent Na+ concentrations) and

freeze-testing twigs for hardiness on the third day resulted in a linear reduction of

hardiness of ﬂower buds of 5.0 °C, 4.5 °C, respectively, compared to deionized Water

(Table 16).

 

Table 16: Cold hardiness of ﬂower buds
measured on 23 Jan. 2004 treated with
selected Na+-salts applied to branches of
‘Jersey’ highbush blueberry on 15 and 16
Jan. 2004.

 

 

 

Treatment LTso CC)
Control -20.0az
Na2804 - l 9.03
NaAC ~15.5b
NaCl -15.0b
P-value _<_0.0001

 

2 means within columns followed by a
different letter are signiﬁcantly different by

Tukgy’s HSD (P=0.05L

92

DISCUSSION

Multiple sprays of NaCl applied to blueberries during the winter resulted in
similar injury symptoms (shoot dieback, ﬂower bud mortality) observed in bluebeny
ﬁelds adjacent to salted roads in west Michigan (Chapter 2), indicating that deicing salt
spray is predominantly responsible for the ﬂower bud loss on bluebeny farms in Ottawa
county.

Consistent with Thompson and Rudder (1986), multiple sprays of salt to the
above-ground portions of plants did not kill plants, whereas the highest rates of soil-
applied NaCl resulted in considerable plant damage evident by early May (at full-bloom).
Injury symptoms in the ﬁeld, as much as complete loss of ﬂower buds, are consistent
with those from the soil salt inundation experiment (mean 97% ﬂower bud loss), but the
degree of shoot and cane dieback from the soil salt inundation study was much more
severe than that seen at all but the most severely affected farms (‘A’ and ‘1’). Excessive
soil salt cannot be considered as a possible explanation for the ﬂower bud loss at the most
exposed sites where high levels of ﬂower bud mortality were observed until more
thorough soil sampling has been performed at those sites, as well as tissue sampling for
internal Na+ and Cl'.

Salt residues on twigs as a result of sprays (Figure 16) were similar to those
observed on twigs adjacent to salted roads (Chapter 2). The fact that similar levels of salt
accumulation, and the range of ﬂower primordia injury, were observed on twigs sampled
during the salt spray trial and from ﬁeld-grown plants (Chapter 2) provides conﬁdence
that deicing salt spray was most likely responsible for injury to blueberry plants in

Ottawa County, Mich. Deicing salt spray also had negative effects on lowbush

93

blueberries adjacent to major Canadian highways (Eaton et al., 1999). These workers
reported the highest concentration of deicing salts on shoots from plants nearest the
highway, and yields as well as number of living ﬂower buds were inversely correlated
with salt concentration on the shoots. Plastic shelters placed over plants reduced salt
levels on shoots and increased numbers of live ﬂower buds and yields, suggesting this
type of barrier is effective at mitigating the damaging effect of deicing salts on lowbush
blueberry.

High levels of Na+ and Cl' remained in the soil samples after ﬂushing with four
liters of ﬂesh water. Control pots contained surprisingly high levels of Na+ (95 ppm) and
Cl' (270 ppm). Soil chloride levels higher than 200 ppm may cause toxicity to
glycophytic and halophytic plant species (Salinity Lab. Staff, 1954). Again, these are the
levels from the soil cores taken just before destructive harvesting of the plants in late
June, after uptake and ﬂushing (due to irrigations) of these ions must have been
occurring. This means that either the soil and/or the irrigation water used by the nursery
contained high Na+ and Cl' levels, or the irrigation (well) water used to maintain the
plants contained high levels of these ions. Since the plants receiving the three lowest salt
levels exhibited less than 30% of the ﬂower bud mortality as the plants receiving the
highest salt level (Figure 17), this could indicate that highbush bluebeny is moderately
tolerant of salt in the root zone. Highbush blueberry is considered somewhat drought-
tolerant (Gough, 1994), and this feature may play a role in a plant’s ability to tolerate
salinity (T al et al., 1979). Also, the root system of highbush blueberry is shallow
(Gough, 1994), so plants may not be exposed to any salts that leach below depths of 20 -

25 cm.

94

Pedersen et al. (2000) measured annual accumulations of Na+ and CI' in soils
adjacent to salted roads and found a gradual accumulation of salts in soils from one year
to the next, and others have addressed the question of whether deicing salts accumulate in
roadside soils over years (Button, 1964; Westing, 1969; Sucoff, 1975; Lumis et al., 1976;
Bryson and Barker, 2002). Soil sampling in salt-affected ﬁelds might help determine
whether soil salt is contributing to the injtuy in Ottawa County bluebeny ﬁelds. It is
possible that plants closest to US 31 at farms ‘A’ and ‘I’, and plants closest to M-45 at
farms ‘B’ and ‘C’, are experiencing a gradual accumulation in shoot and cane tissues that
are contributing to high levels of ﬂower bud mortality. Farms ‘A’ and ‘I’ appear to be
suffering the highest levels of ﬂower bud loss and reduced yields.

Deicing salts decrease the cold hardiness of highbush bluebeny ﬂower buds;
fluther, it is probable that decreases in cold hardiness ﬁom deicing salts are greater under
ﬁeld conditions than those measured under controlled circumstances. In the case of cold
hardiness study #2, it is likely that ﬁeld conditions are such that very high levels of
deicing salt spray are being generated following a snow event for widely varying periods
of time, resulting in a dynamic environment. These extreme conditions probably result in
a situation where known trends relating to plant cold hardiness responses are not easily
predicted under these speciﬁc circumstances.

Bud position did not affect ﬂower primordia mortality, except in salt spray study
#2 (data not shown). This is not consistent with observations on highbush bluebeny
(Biennann et al., 1979; Hancock et al., 1987), or Vitis labruscana ‘Concord’ (Stergios
and Howell, 1977), where bud hardiness was signiﬁcantly affected by bud position. The

reason for this could be that treated shoots were usually vertical or nearly so, meaning the

95

salt treatments, applied to the point of drip, would drip down the length of the shoot due
to gravity, concentrating greater quantities of salt around the lower ﬂower buds. This
might mean that their cold tolerance was affected to a greater degree than the terminal
ﬂower buds due to greater salt exposure, negating their greater cold hardiness. Salt spray
applications for the cold hardiness evaluations were conducted during the mid-winter
months when all ﬂower buds are expected to be at a more or less equal stage of cold
tolerance, which would likely obscme the effect of bud position (development) on cold
tolerance. Differences in hardiness by bud position might be expected to appear if these
same studies were conducted in late fall / early winter, or late winter / early spring.

Salt reduced the cold tolerance of bluebeny ﬂower buds almost immediately
(study #4). The consistent effect of NaCl in decreasing the cold hardiness of ﬂower buds
agrees with Sucoff (1975), Sucoff et al. (1976), and Sucoff and Hong (1976a). How salt
exposure compromises hardiness is unknown. The reduction in ﬂower bud hardiness
resulting ﬂour salt exposure could be related to desiccation, or perhaps Na+ or Cl' toxicity
(Sucoff, 1975). However, Northover (1987) found no evidence of crystallized NaCl
deposits inducing desiccation in peach shoots; it was found that NaCl toxicity only
occurred when present in solution. The data ﬁom experiments 5 and 6 do not indicate a
speciﬁc ion toxic effect, as Na+ and Cl' deicing salts both reduced the cold tolerance of
ﬂower buds, except for Na2804. Results ﬁom experiment 6 seem to suggest that the
toxic effects of Na+ can be somewhat mitigated by sulfate (S04), which might explain the
lack of effect on cold tolerance by Na2S04. This could also mean that N82S04 is not an
effective deicer for this same reason (i.e., S04 mitigates the depression on the ﬁeezing

point of water by Na).

96

One way Na” in particular can desiccate ﬂower buds relates to the hydration
effect on the ion itself. The radius of Na+ is 0.98 Angstroms (A) in the dehydrated state
and 7.90 A in the hydrated state (F 0th, 1978). Compare this to Li+ (0.78 A dehydrated,
10.03 A hydrated), and K” (1.33 A dehydrated, 5.32 A hydrated) (Foth, 1978). Clearly,
Na+ has a high affinity for water. Regarding the deicing materials tested in this study,
NaCl and NaAC would likely have a stronger desiccating potential based on the Na+
content of these materials, as opposed to Ca2+ (CaClz), Mg2+ (MgClz), and K+ (KCl).

The reduction in cold tolerance by salt exposure in highbush blueberry ﬂower
buds has never been quantiﬁed or described in any way prior to these studies. Also, the
decreases in cold tolerance occurred at temperatures that usually occur in an average
winter in West Michigan. This means that these observed responses by way of reduced
cold tolerance are reﬂective of real-world observations, hence, signiﬁcant to blueberry
farms at-risk of experiencing deicing salt injury.

Cold hardiness was affected most severely by NaCl compared to Na2804, NaAC,
MgClz, CaC12 and KC]. Based on LTso levels, it would seem that KCl might be a
promising candidate for reducing injury along US 31 and M-45; at least on stretches of
those highways adjacent to the most seriously affected farms in Ottawa County,
Michigan. It is not known at this time where any of these alternative deicers are being
used for deicing purposes in Michigan. Potassium chloride is effective down to -11.0 °C
(MDOT, 1993). The lowest effective temperature of KCI is lower than that of NaCl, so
this should not exclude KCl from use as a possible deicing alternative to NaCl.

Information regarding Na2S04 as a deicing material could not be formd.

97

Sodium toxicity is reportedly not as widespread as CT toxicity, and is mainly
related to low Ca2+ levels in saline substrates, or high Cay/Na+ ratios in combination with
poor soil aeration (Marschner, 1990). Experiments with many species showed that Cl’
damage was more severe than Na+, and work with Rubus spp. treated with NaCl
demonstrated that Cl' accumulated in the shoots faster than Na“, and the severe necrosis
was attributed primarily to Cl' (Wright et al., 1992). In spite of these ﬁndings and many
others related to salt injury to plants, there does not seem to be uniform agreement in the
literature on how salt damages dormant plants.

Short days, low ambient relative humidity, and extracellular ice formation during
freezing temperatures, all contribute to cell dehydration. The movement of cellular water
to extracellular ice crystals is an especially important strategy for cold tolerant plants
(Kuroda et al., 2003). However, excessive dehydration is lethal to cells (Kuroda et al.,
2003).

Deep supercooling is a freeze-avoidance mechanism for some plant tissues (i.e.,
blueberry ﬂower buds, and xylem ray parenchyma cells [XRPCS] in most temperate zone
trees) that seems to suggest that the cold acclimation process involves reduction or
elimination of ice nucleating sites in such tissue cells, development of effective barriers
to ice nucleation events, or both (Burke et al., 1976). In XRPCs that undergo deep
supercooling, a low temperature exotherm is produced below -20 0C (Kuroda etal.,
2003). Supercooling is also a ﬁeeze-avoidance mechanism that occurs in ﬂower buds,
XRPCs, and some other tissues, and occurs at higher temperatures than deep

supercooling.

98

 

Eltlllirvl i ,

Since blueberry ﬂower buds tolerate winter cold by deep supercooling (Quamme,
1991), salt exposure may reduce bud hardiness by disrupting this process. One way this
might occur is by desiccating, or depressing the freezing point of the ﬂower bud scales,
which are the ﬁrst tissues to freeze when ﬂower buds ﬁ‘eeze (Ishikawa and Sakai, 1981).
This would then allow the ﬂower primordia axis to desiccate and/or freeze, destroying the
freeze avoidance mechanism(s) that may already have occurred. The ﬂower primordia
would logically suffer cold injury. Another explanation might be that NaCl damages the
bud scales, reducing the insulating and anti-desiccating protection provided by the bud
scales. When ﬂower buds were dissected following these controlled freezing studies, the
bud scales of salt-treated twigs often appeared tattered and loosely connected to the
ﬂower buds (personal observation), giving rise to this theory. Exposure to NaCl might
compromise the integrity of the individual bundle ﬁbers to the point that strong wind
gusts loosen the bud scales. This could make the ice nucleation event easier. Flower and
leaf buds are important organs for reproduction and vegetative proliferation in the
following growing season, but they are often also more susceptible to freezing than are
twig tissues (Ishikawa ct al., 1997).

The highest soil salt level (i.e., 27g'L'l NaCl) had a more severe effect on ﬂower
bud mortality in highbush blueberry than the highest salt level in the salt spray trial
(32g-1;l NaCl) (Figures 15 and 18), indicating that salt spray is less harmful to the
survival of ﬂower buds than soil borne salts. However, the overall level of injury to
highbush bluebeny plants in the ﬁelds as assessed in the spring farm surveys suggests
that salt spray is the probable factor. All salts with known deicing properties decreased

the cold tolerance of highbush bluebenies in this study, although NaCl appeared to be the

99

most harmful (Tables 13 through 16). Sodium sulfate did not decrease cold tolerance, but

it is unknown whether it possesses deicing properties.

100

LITERATURE CITED

Biermann, J ., C. Stushnoﬁ‘ and M.J. Burke. 1979. Differential thermal analysis and
freezing injury in cold hardy blueberry ﬂower buds. J. Amer. Soc. Hort. Sci. 104:44-449.

Bowers, M.C. and J .H. Hesterberg. 1976. Environmental implications of highway
deicing agents on white pine in Marquette County, Michigan. The Michigan Botanist
15:75-89.

Bryson, G.M. and A.V. Barker. 2002. Sodium accumulation in soils and plants along
Massachusetts’s roadsides. Commun. Soil Sci. Plant Anal. 33:67-78.

Burke, M.J., L.V. Gust, H.A. Quamme, C.J. Weiser and PH. Li. 1976. Freezing and
injury in plants. Ann. Rev. Plant Physiol. 27 :507-528.

Button, E.F. 1964. Inﬂuence of rock salt used for highway ice control on mature sugar
maples at one location in central Connecticut. Supplementary report #3a. Connecticut

State Highway Department.

Eaton, L.J., J. Hoyle and A. King. 1999. Eﬂ‘ect of deicing salt on lowbush blueberry
ﬂowering and yield. Can. J. Plant Sci. 79:125-128.

Flinn, CL. and EN. Ashworth. 1994. Seasonal changes in ice distribution and xylem
development in bluebeny ﬂower buds. J. Amer. Soc. Hort. Sci. 11911176-1184.

Foth, H.D. 1973. Fundamentals of soil science, 6‘h Edition. P. 194. New York: John
Wiley and Sons.

Gough, RE. 1994. The highbush bluebeny and its management. Pp. 59-65. New York:
Food Products Press.

Hancock, J .F ., J .W. Nelson, H.C. Bittenbender, P.W. Callow, J.S. Cameron, S.L. Krebs,
M.P. Pritts and CM. Schumann. 1987. Variation among highbush blueberry cultivars in
susceptibility to spring ﬁost. J. Amer. Soc. Hort. Sci. 112:702-706.

Hipp, B.W. and G.W. Langdale. 1971. Commun. Soil Sci. Plant Anal. 2:237.

Ishikawa, M. and A. Sakai. 1981. Freezing avoidance mechanisms by supercooling in
some Rhododendron ﬂower buds with reference to water relations. Plant and Cell
Physiol. 22:953-967.

Ishikawa, M., W.S. Price, H. Ide and Y. Arata 1997. Visualization of freezing

behaviors in leaf and ﬂower buds of full-moon maple by nuclear magnetic resonance
microscopy. Plant Physiol. 115:1515-1524.

101

Kuroda, K., J. Kasuga, K. Arakawa and S. F ujikawa. 2003. Xylem ray parenchyma cells
in boreal hardwood species respond to subfreezing temperatures by deep supercooling
that is accompanied by incomplete desiccation. Plant Physiology 131:736-744.

Lumis, G.P., G. Hofstra and R. Hall. 1976. Roadside woody plant susceptibility to
sodium and chloride accumulation during winter and spring. Can. J. Plant Sci. 56:853-
859.

MDOT. 1993. The use of selected deicing materials on Michigan roads: Environmental
and economic impacts. Public Sector Consultants (with MDOT). Lansing, MI.

Marschner, H. 1990. Mineral nutrition of higher plants. Pp. 533-537. San Diego, CA.
Academic Press.

Northover, J. 1987. NaCl injury to dormant roadside peach trees and its effect on the
incidence of infections by Leucostoma spp. Phytopathology 77:835-840.

Pedersen, L.B., T.B. Randrup and M. Ingerslev. 2000. Effects of road distance and
protective measures on deicing NaCl deposition and soil solution chemistry in planted
median strips. J. Arbor. 26:238-244.

Quamme, H.A. 1991. Application of thermal analysis to breeding fruit crops for
increased cold hardiness. HortScience 26:513-517.

Salinity Laboratory Staff. 1954. Diagnosis and improvement of saline and alkaline soils.
Agriculture handbook #60, USDA. U.S. Government Printing Office, Washington, DC.

Stergios, B.G. and G.S. Howell. 1977. Effect of site on cold acclimation and
deacelimation of Concord grapevines. Am. J. Enol. and Vitic. 28:43-48.

Sucoff, E. 1975. Effect of deicing salts on woody vegetation along Minnesota roads.
Investigation #636, Minn. Ag. Exp. Sta. Tech. Bull.

Sucoff, E., S.G. Hong and A. Wood. 1976. NaCl and twig dieback along highways and
cold hardiness of highway versus garden twigs. Can. J. Bot 54:2268-2274.

Sucoff, E. and S.G. Hong. 1976a. Effects of NaCl on cold-hardiness of Malus spp. and
Syringa vulgaris. Can. J. Bot. 54:2816-2819.

Tal, M., A. Katz, H. Heikin and K. Dehan. 1979. Salt tolerance in the wild relatives of
the cultivated tomato: proline accumulation in Lycopersicon esculentum Mill., L.
peruvianum, and Solanum pennelli Cor. treated with NaCl and polyethylene glycol. New
Phytol. 82:349-355.

102

Thomas, G.W. 1982. Exchangeable cations. Pp. 159-165. In: AL. Page et al. (ed.).
Methods of soil analysis, part 11. Second ed. Agronomy Monogram 9. ASA and SSSA,
Madison, Wis.

Thompson, J .R. and A.J. Rutter. 1986. The Salinity of Motorway Soils. IV. Effects of
sodium chloride on some native British shrub species, and the possibility of establishing
shrubs on the central reserves of motorways. J. Appl. Ecol. 23:299-315.

Westing, AH. 1969. Plants and salt in the roadside environment. Phytopathology
59:1 174-1 181.

Wright, G.C., K.D. Patten and M.C. Drew. 1992. Salinity and supplemental calcium
inﬂuence growth of rabbiteye and southern highbush blueberry. J. Amer. Soc. Hort. Sci.
1 17:749-756.

Zobel, A. and J .E. Nighswander. 1990. Accumulation of phenolic compounds in the
necrotic areas of Austrian and red pine needles due to salt spray. Ann. Bot. 66:629-640.

103

CHAPTERIV

CONCLUSIONS

104

CONCLUSIONS

These studies indicate that twig dieback and ﬂower bud mortality in blueberry
ﬁelds along highways in Michigan were the result of windbome salt spray deposited on
twigs. This conclusion is based on the fact that salt deposition and ﬂower bud mortality
were greatest on plants closest to the road. Flower bud mortality was generally greatest
on farms east of a divided major highway, which was downwind of the prevailing wind
direction. Secondly, treating plants with salt sprays induced twig dieback and ﬂower bud
mortality, that appeared identical to the injury on plants next to roads. Salt sprays
resulted in similar salt levels on twigs as observed on twigs of bushes next to roads,
although salt deposition levels on ﬁeld-grown plants were probably reduced by
precipitation events.

Soil salt accumulation may also contribute to plant injury close to roads, but only
at the most severely affected sites (farms ‘A’ and ‘1’). Intermediate levels of NaCl
applied to the soil of potted plants resulted in ﬂower bud mortality and twig dieback
similar to plants next to salted roads. Highest rates resulted in severe injury, including
complete loss of ﬂower buds and negligible growth. Some plants closest to the highway
also exhibited chronic dieback and poor growth. Because soil salt levels were not
measured at varying distances ﬁ'om the road, the inﬂuence of soil salts on plant injury
cannot be determined.

One observation made at severely affected farms is that many plants set few or no
ﬂower buds. High soil and/or tissue levels might be contributing to this aberrant growth.

Elevated soil salt levels could be responsible for increasing plant tissue salt levels to the

105

extent that ﬂower bud development is suppressed, but not toxic to the plant. This could
be studied in the future by detailed soil and tissue sampling.

Salt exposure decreased the cold hardiness of ‘Jersey’ and ‘Bluecrop’ highbush
blueberry ﬂower buds. Flower bud mortality in ﬁelds adjacent to major roads in west
Michigan may result ﬁom reduced hardiness and subsequent winter injury since typical
winter injury symptoms are similar to those induced by salt exposure. The results of the
cold hardiness spray study #2 suggests that NaCl decreases cold hardiness to a greater
extent in the ﬁeld than that which was measured under controlled conditions. This makes
sense, as it is not possible to duplicate the variables inﬂuencing salt spray injury in the
ﬁeld under controlled conditions, meaning that it is likely that NaCl causes more serious
injury in the ﬁeld than observed after controlled salt treatments. This would translate into
greater yield losses for the grower than that which the regression models described
(Chapter 2).

How salt reduces hardiness is not clear. However, all salts tested, except Nasta.
decreased cold hardiness, indicating that the effect of salt on hardiness is not a speciﬁc
response to Na+ or Cl'. This hints at a physical effect, since differences in ionic radii
between the hydrated and dehydrated state for Na+ indicate a high afﬁnity for water.
Differences between the hydrated and dehydrated ionic radii for CI' were not found in the
literature, but if Cl' can penetrate cellular membranes passively with Na+ in the case of
NaCl exposure, this would explain why NaCl always decreased cold hardiness greater .
than the other salts tested. Sulfate may partially mitigate the toxic effects of Na+, as

evidenced by the fact that Na2804 did not affect the cold tolerance of ﬂower buds.

106

More needs to be known about how NaCl is affecting other woody vegetation,
groundwater supplies, and the soil structure in areas where deicing materials are utilized.
Since deicing salts will continue to be applied during the winter months throughout
Michigan for the forseeable future, surveying other fruit and nursery crops would give a
better idea of other plant species that are sensitive (or tolerant), as well as revealing
additional economic losses.

Deicing salts have been in use for about 60 years, and injury has been reported
occurring to plants surveyed as part of this work for about the last 10 years. Given the
apparent increasing decline in the general health of blueberry plants at some of the most
severely affected farms as seen during the May farm surveys, it is reasonable to predict
that plant mortality will soon be reported to blueberries growing along US 31, especially
if deicing salt usage increases. Usage will likely increase if Census Bureau predictions,
that population growth in Ottawa county will increase 20% over the next 10 years (US
Census Bureau, 2000), are accurate, as this will result in an increase in vehicular trafﬁc
on US 31 and M45. Vehicular traffic on US 31 has steadily increased within the last 8
years (Tim Croze, MDOT, pers. comm.) Average daily trafﬁc (ADT) on US 31 north of
M-45 increased by 20% from 1997 to 2001 (Tim Croze, MDOT, pers. com.) This may
be because the population of Ottawa County increased nearly 27% during the 19905, and
is projected to increase by 30% or greater by the year 2025 (U .8. Census Bureau, 2000).
An increase in trafﬁc volume will require more timely NaCl applications, perhaps with
increased frequency, and with more salt spray being whipped-up by the escalating
vehicular trafﬁc, which could potentially result in increased plant injury due to deicing

salt.

107

The use of sprayable materials to protect against salt spray injury remains elusive.
An attempt was made to ﬁnd a sprayable material that might protect the plants from
deicing salt spray injury. After a preliminary trial to test the products for phytotoxicity,
spray trials were performed under controlled conditions and in the ﬁeld. No material
protected ﬂower buds (Appendix 23).

Injury to blueberries in west Michigan might be reduced by applying less
phytotoxic deicing salts along stretches of highway adjacent to blueberry plantings,
applying just enough deicing material to achieve the desired result, using precision
application equipment, or planting salt-tolerant coniferous tree species as a screen against
wind-blown salt spray. New blueberry plantings should not be planted within 500 feet of

any road receiving deicing salt applications in the winter months.

108

APPENDICES

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832$. mdwn. FREE 0952. 2:03.. 88 I moo?

 

122

. \
Q ’ . o
0
Gas station

    
  

 

Mixed deciduous
species wooded
O
o 6 ° area
0
o 0 °
3 o
0
° 0
Acer 6 ’9’ ‘ .
rubrum\ , ,
0 o
O ’ ’
O O
«O 0
O
/ ' °
0“ O .
Northbound
. O
«o ’ o ’
. O
.0
’ o
0. o o .
O
O O
O O
I" .
. . § 0
O. N
, o ’ o
o
/ 0 o ’
O
Southbound o ‘
O
o ’ ,
Barn —*>|:] ’

 

- 2 lane divided highway
Scale: 1cm = 24.5m

Appendix 14: Schematic map of farm ‘A’, Ottawa County, Mich., showing surveyed
plant locations, structures, and vegetation.

123

[farm B

 

Betula
pendula
O O O 0 O O O O O 0 O (2 68‘)
Deciduous shrubs
O O
o o o o . . . . .
o o o . . . o .
. ° 0 O o o . o o o
0 o o o . , .
o o o o , . . o o o
O o o o . . . o O O
O
O O O O O O O O

 

Pinus s obus (2 ea.) Junipe virginiana (2 ea.)
Pinus resinosa (5 ea.) N

Quercus rubra
Picea abies
(5 681-)

Betula pendula

Sb, 4 .. Farm C

 

 

"' 0° 0
I . o o o o o o o .
O
....’ o o o o o
.9... O 0 O O O O Q
.0... O O O 0 O O
O
0
....° 0 o . 0 o o ’
...,’ o o o o o o .
O

— 2 Lane undivided highway
Farm access road
Scale (Farm B): 1cm = 28m; Farm C: 1cm = 38.6m

 

O
O
0
Dead pmes
O o
O
O O
O
O O
O
0
° 0
O
’ o
. O
O
O . .
0
O 0

Appendix 15: Schematic map of farm ‘B’ (north of M-45 - top), and farm ‘C’ (south of
M-45 — bottom), Ottawa County, Mich., showing surveyed plant locations, structures,

and vegetation.

124

Farm D

 

 

 

 

Mixed deciduous and
evergreen cover
0
S ’ ’ o o o o
O O O O O
O O O O
O O O
o 9 °
0 O O
O O O O O . O
O
O O O O O

 

 

— 2 lane paved secondary road
2 lane unpaved secondary road
Scale (Farm D): 1cm = 28.3m; Farm E: lcm = 6.8m

 

Appendix 16: Schematic map of farms ‘D’ (east of 144th Avenue — top), and farm ‘E’

(west of 144th Avenue - bottom), Ottawa County, Mich., showing plant locations,
structures, and vegetation.

125

 

’ O,\ Northbound
Acer
rubrum
O
. f
Southbound N
O
. O O

 

O
- 2 Lane divided highway
Scale: 1cm = 4.9m

Appendix 17: Schematic map of farm ‘F’, Ottawa County, Mich., showing surveyed
plant locations, structures, and vegetation.

126

Far G

Northbound

° Southbound

Farm H

   

 

 

 

 

Acer
saccharinum
Mixed evergreen and
deciduous cover. \
—-a—— l 5
O O O O O O O ‘ ‘ ‘
O O
O O
O 6
Acer ﬂo Picea abies
rubrum . . . O K0 ea.)
(2 ea.) 9 O O OO

— 2 Lane divided highway

_ 2 Lane unpaved road Scale (Farm G): lcm = 10m; Farm H: 1cm = 22.2m
Appendix 18: Schematic map of farms ‘G’ (west of US 31 - top), and farm ‘H’ (west of
US 31 — bottom), Ottawa County, Mich., showing surveyed plant locations, and
vegetation.

127

Hardwood
vegetation
cover

   

 

 

0 *Wooded area (hardwood and

O
comferous spec1es)
O
O
O O .
Q 0
O
. O
o . ° 0
O O
o
O
0 ° °
. O O
O
O O
O
. O
O
0 o
O
. , N
O . Q
Q
. O
0
. O
O
O
Q
g o o

 

 

_ 2 Lane paved secondary road
_ 2 Lane divided highway
Scale: 1cm = 18.4m

Appendix 19: Schematic map of farm ‘1’ (east of US 31), Ottawa County, Mich.,
showing plant locations and vegetation.

128

Farm J

Picea pungens

 

o
(21 each)
1 o
O O
o
o
. o
o o
o
. O
’ o
o
o
o
o
g o
o
o
o
o o
g o
o
o
9 o
o o ’
o
o
o
9
Evergreen
vegetation
cover
(Pinus spp)

 

 

_ 2 Lane divided highway
Scale: lcm = 8.4m

Appendix 20: Schematic map of farm ‘J ’ (east of US 31 and south of farm ‘1’), Ottawa
County, Mich., showing surveyed plant locations and vegetation.

129

Farm K

 

Prunus
virginiana

Utility Pole

 

009

 

Appendix 21: Location of farms ‘K’ (east of 120'” Avenue — top), Ottawa County, Mich.,
and plants from Study 1, 2002 and 2004.

 

2 lane unpaved road
Scale: 1cm = 28.6m

130

Deciduous vegetation
cover (mixed species)

 

 

   

Populous sp.
(4 each)

0

0
Appendix 22: Location of farms ‘L’ ( . of 1-96), uskegon County, Mich., and plants
from Study 1, 2002 and 2004.

— 2 Lane unpaved road
_ 2 Lane paved road
_ 2 Lane divided highway

Scale: 1 em = 27.5m

131

Appendix 23

Several materials were tested to see if protection from salt spray could be
achieved using sprayable materials. Two trials were set-up at farm ‘J’ in November (trial
#1) and early December (trial #2) 2003 in a randomized complete block design. Each
block was at a different distance to the nearest salted road (US 31). Data were collected
at full-bloom, coinciding with the May 2004 farm surveys, and consisted of counting the
number of living and dead ﬂower buds on ten randomly selected twigs.
Table 1: Mean ﬂower bud mortality of various hypothetical protective materials applied
to blueberry ﬂower buds, farm ‘1’, Ottawa, County, Mich., 2003 -— 2004 (materials
applied on 25 Nov. 2003 [trial #1] and 4 Dec. 2003 [trial #2], and ﬂower bud counts

performed on 5 May 04). Materials tested to investigate possible protection from
ambient salt spray (US 31).

 

 

 

 

Protective Coating Trial #1

Material Used / Otv. Applied (L) Mean Flower Loss (%)
Sunspray 6E / 22.7 36az
Kaolin Clay/ 15.1 51a
Control (D1H20)/ 11.3 22a
Cerenat—l%/15.1 42a
Moisturin/ 22.7 333
Unsprayed Control 513
P-value 0.49

 

2 means within columns followed by a different letter are signiﬁcantly different by
Tukey’s HSD (P=0.05).

 

Protective Coating Trial #2:
Material Used / Qty. Applied (L) Mean Flower L0§_s (%)

 

Whitewash (10%)/ 15.] 32b2
Control (D1H20)/ 11.3 45ba
Sunspray UF (2x) / 9.5 65a

P-value 0.10

 

2 means within columns followed by a different letter are signiﬁcantly different by
Tukey’s HSD (P=0.05).

 

132

   

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