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Michael Douglas Von Weihe

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HIGH TUNNEL PRODUCTION OF RED RASPBERRY (Rubus idaeus L.): COLD
HARDINESS AND AN ECONOMIC ANALYSIS

By

Michael Douglas Von Weihe

A THESIS

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

MASTER OF SCIENCE

Horticulture

2009

ABSTRACT

HIGH TUNNEL PRODUCTION OF RED RASPBERRY (Rubus idaeus L.): COLD
HARDINESS AND AN ECONOMIC ANALYSIS

By
Michael Douglas Von Weihe

Interest in using high tunnels for producing red raspberries is increasing in temperate
climate regions of the United States. High quality fruit can be produced under ttmnels but the
profitability of this system has not been investigated in Michigan under current economic
conditions. Additionally, no work has been done to describe how the use of a 3-season tunnel
during the growing season may influence cold hardiness during the winter. Objectives of this
work were to: 1) determine the profitability of floricane- (FF) and primocane-fruiting (PF)
raspberry cultivars in tunnels under certain costs and berry prices, 2) characterize cold
acclimation of high tunnel-grown raspberry plants, and 3) determine carbohydrate levels in
acclimating plants and describe their relationship to cold hardiness. Crop values at full production
for one acre of FF and PF tunnel raspberries were $60,060 and $71,520, respectively. Break-even
yields (yields necessary to cover costs) for PF types were lower than for FF types, indicating PF
cultivars have a higher potential for profit under tunnels. Cold hardiness of tunnel and field
raspberry tissues were similar on most dates in the autumn, suggesting cold acclimation under
covered, 3-season tunnels and in the field may be similar. Bud primordia and cambium tissues of
‘Nova’ were typically more cold hardy than ‘Canby’ and ‘Encore’ during acclimation and in mid-
winter. Concentrations of the soluble carbohydrate raffmose were higher in ‘Nova’ than the other
two cultivars. All soluble carbohydrate levels were positively correlated with hardiness while
starch was negatively correlated. Early high tunnel plastic removal increased hardiness of bud

primordia but had no effect on cambium hardiness.

Cepyfight by
Michael Douglas Von Weihe
2009

DEDICATION

To my parents, Doug and Becky Von Weihe for their unwavering support in all I do

and to Mike J.

iv

Acknowledgements

I would first like to extend my sincere thanks to my major professor, Dr. Eric
Hanson. He never ceased to be encouraging to me throughout my time at Michigan
State. I learned a great deal from his approach to conducting research, professional
interaction, and style of teaching. For his patience and kindness to me while completing
my degree, I am very grateful.

I would also like to thank my committee members, Dr. Greg Lang and Dr. Roy
Black. Their insightful suggestions caused me to think more critically about my research.

A special thanks to Dr. Wayne Loescher for the use of his lab, his guidance in
conducting carbohydrate determinations, and his scientific perspective.

Thank you to Dave Francis and the staff at the Southwest Michigan Research and
Extension Center for their help in managing and picking the raspberry plots. Thanks to
Lynne Sage for introducing me to the wonderful world of controlled freezing
experiments. I’d also like to thank the many people who have assisted in data collection
during my time at MSU; Britt Uecker, Craig Noble, Laura Havenga, and Jennifer Pitylak.

Finally, I want to thank all of the HOGS members and graduate students who
have made my time at Michigan State so meaningful. Thanks to my officemate, Letizia
Tozzini, for many enjoyable conversations. A big thank you to my roommates and fellow
horticulturists Aaron Warsaw and Theoharis Ouzounis for sharing advice from their

graduate school experiences and for their friendship.

TABLE OF CONTENTS

LIST OF TABLES ........................................................................................................ viii
LIST OF FIGURES .......................................................................................................... x
CHAPTER 1 ..................................................................................................................... 1
REVIEW OF LITERATURE ........................................................................................... 1
Fresh Raspberry Production ...................................................................................... 1
High Tunnels ............................................................................................................. 2
Economrcs .......................................................................... 4

High Tunnel Benefits and Concerns .................................................................. 6
Freezing Stress and Cold Hardiness ......................................................................... 8
Mechanisms of Plant Injury by Freezing Temperatures .................................... 8
Freezing Resistance and Mechanisms of Plant Survival ................................... 9
Freezing Avoidance ................................................................................... 10

Freezing Tolerance ..................................................................................... 12

Donnancy and Cold Hardiness in Woody Plants and Raspberry .................... 13
Photoperiod ................................................................................................ 14

Low Temperatures ..................................................................................... 15

Methods to Evaluate Cold Hardiness ............................................................... 16
Carbohydrates ......................................................................................................... 19
Soluble Carbohydrates ..................................................................................... 19

Starch ............................................................................................................... 22
Summary ................................................................................................................. 22
Literature Cited ....................................................................................................... 24
CHAPTER 2 ................................................................................................................... 34
THE ECONOMICS OF 3-SEASON HIGH TUNNEL RASPBERRY PRODUCTION
................................................................................................................................. 34
Abstract ................................................................................................................... 34
Introduction ............................................................................................................. 35
Materials and Methods ............................................................................................ 39
Costs ................................................................................................................. 39

Yields ............................................................................................................... 41

Berry Prices ...................................................................................................... 42
Wholesale Raspberry Volume ......................................................................... 43
Break-even Analysis ........................................................................................ 43

Results and Discussion ........................................................................................... 43
Literature Cited ....................................................................................................... 49
CHAPTER 3 ................................................................................................................... 59

COLD HARDINESS AND CARBOHYDRATE COMPOSITION OF RED
RASPBERRY (Rubus idaeus L.) GROWN UNDER 3-SEASON HIGH TUNNEL AND

FIELD CONDITIONS .................................................................................................... 59
Abstract ................................................................................................................... 59
Introduction ............................................................................................................. 60

vi

Materials and Methods ............................................................................................ 65

High Tunnel and Field Cultivar Comparisons ................................................. 65
Cold Hardiness Determination ................................................................... 66
Carbohydrate Determination ...................................................................... 68

Potted Raspberry Experiment .......................................................................... 70

Statistical Analysis ........................................................................................... 71

Results ..................................................................................................................... 72

High Tunnel and Field Cultivar Comparisons ................................................. 72
Cold Hardiness ........................................................................................... 73
Carbohydrates ............................................................................................ 74
LT50 and Carbohydrate Correlations ......................................................... 77

Potted Raspberry Experiment .......................................................................... 78
Cold Hardiness ........................................................................................... 78
Carbohydrates ............................................................................................ 79

Discussion ............................................................................................................... 79
Conclusions ............................................................................................................. 85
Literature Cited ....................................................................................................... 87

vii

LIST OF TABLES

Table 2-1. Pre-pant and establishment costs associated with planting one acre of red
raspberries under 3-season high tunnels ......................................................................... 52

Table 2-2. Year 1 costs for producing one acre of red raspberries under 3-season high
tunnels ............................................................................................................................. 53

Table 2-3. Year 2 costs for producing one acre of red raspberries under 3-season high
tunnels ............................................................................................................................. 54

Table 2-4. Year 3-7 costs for producing one acre of red raspberries under 3-season high
tunnels ............................................................................................................................. 55

Table 2-5. Table 2-5. Annual allocated costs for producing one acre of red raspberries
under 3-season high tunnels at full production ............................................................... 56

Table 2-6. Total allocated costs, marketable yield, and crop value from one acre of
primocane-fruiting (PF) and floricane—fi'uiting (FF) raspberries under 3-season high
tunnels (F 0.8. farm) ...................................................................................................... 57

Table 2-7. Break-even yieldz (lbs) for one acre of floricane-fi'uiting (FF) and primocane-
fruiting (PF) raspberries under 3-season high tunnel production at various wholesale
prices ............................................................................................................................... 57

Table 3-1. Mean LT50z values and number (n) of observations if less than 3 for bud

primordia and cambium tissues of red raspberry cultivars grown under high tunnel and
field conditions in 2007-08 ............................................................................................. 96

Table 3-2. Mean LT50z values for bud primordia and cambium tissues of red raspberry
cultivars grown under high tunnel and field conditions in 2008 .................................... 97

Table 3-3. Mean percent dry weight of carbohydrates present in cane tissues of red
raspberry cultivars grown under high tunnel and field conditions in 2007-08 ............. 101

viii

Table 3-4. Mean percent dry weight of carbohydrates present in cane tissues of red
raspberry cultivars grown under high tunnel and field conditions in 2008 .................. 102

Table 3-5. Pearson correlation coefficients for cambium LT50 values of red raspberry
cultivars (‘Canby’, ‘Encore’, and ‘Nova’) and percent dry weight of fructose, glucose,
sucrose, raffinose, starch, total soluble carbohydrates, and total nonstructural
carbohydrates in cane tissue during the winter of 2007-08 .......................................... 104

Table 3-6. Pearson correlation coefficients for cambium LT50 values of red raspberry
cultivars (‘Canby’, ‘Encore’, and ‘Nova’) and percent dry weight of fi'uctose, glucose,
sucrose, raffinose, starch, total soluble carbohydrates, and total nonstructural
carbohydrates in cane tissue during cold acclimation in 2008 ..................................... 105

Table 3-7. Pearson correlation coefficients for cambium LT 50 values of 'Heritage' red
raspberry and percent dry weight of fructose, glucose, sucrose, raffinose, starch, total
soluble carbohydrates, and total nonstructural carbohydrates in cane tissue during the
winter of 2007-08 .......................................................................................................... 106

Table 3-8. Mean percent dry weight of carbohydrates present in cane tissues of potted
raspberry plants grown under a high tunnel and moved outside at monthly intervals in the
fall of 2008. Carbohydrates were sampled on 6 Nov. 2008 and means are across all
removal dates (14 Aug., 11 Sep., 9 Oct., and 6 Nov. (not removed)) .......................... 108

Table 3-9. Pearson correlation coefficients for cambium LT50 values of potted red

raspberry plants and percent dry weight of fructose, glucose, sucrose, raffinose, starch,
total soluble carbohydrates, and total nonstructural carbohydrates in cane tissue on 6 Nov.
2008 ............................................................................................................................... 109

ix

LIST OF FIGURES

Figure 2-1. Number of flats (in thousands) of twelve, 6 oz clarnshell containers of fresh
red raspberries shipped in the United States from 2006-08. Stacked bars represent
volumes and their place of origin (California-Central, California-South, Chile, and
Mexico). Data compiled by Laura Havenga .................................................................. 58

Figure 2-2. Break-even yield (lbs) for one acre of floricane—fruiting (FF) and primocane-
fruiting (PF) raspberries under 3-season high tunnel production at various wholesale

prices. Arrows indicate average prices from the Detroit Terminal Market during harvest
periods for FF ($3.90/lb) and PF ($4.80/1b) raspberries from 2006-08. ............. A ............ 59

Figure 3-1. Maximum and minimum ambient air temperatures at the Southwest Michigan
Research and Extension Center (SWMREC) in Benton Harbor, MI fiom 15 Oct. to 20 Mar.
in 2007-2008 (top) and 2008-2009 (bottom). Solid arrows indicate dates where multiple
cultivars were sampled. Arrows with dots indicate dates where only ‘Heritage’ was sampled.
Bold arrows indicate high tunnel plastic removal (14 Nov. 2007 and 11 Nov. 2008) ......... 93

Figure 3-2. Maximum and minimum temperatures for high tunnel and ambient conditions
in 2008. High tunnel temperatures from 8 Aug. to 8 Oct. are an average of 3 data loggers
at 1.5 m height in the raspberry canopy. High tunnel temperatures from 10 Oct. to 29
Oct. are an average of 3 data loggers at 1.4 m height above the raspberry canopy.
Ambient conditions are recorded from an automated weather station less than 200 m from
the high tunnel. The arrow indicates the date tunnels were enclosed with sides and ends
(17 Oct.) .......................................................................................................................... 94

Figure 3-3. Accumulated growing degree days (GDD), with a base temperature of 10 °C,
for 3-season high tunnel and ambient conditions in 2008. High ttmnel GDD from 8 Aug.
to 8 Oct. are an average from 3 data loggers at 1.5 m height in the raspberry canopy.
High tunnel GDD from 10 Oct. to 29 Oct. are an average from 3 data loggers at 1.4 m
height above the raspberry canopy. Ambient conditions are recorded from an automated
weather station less than 200 m fiom the high tunnel. The arrow indicates the date
tunnels were enclosed with sides and ends (17 Oct.) ...................................................... 95

Figure 3-4. Mean LTso values of bud primordia (top) and cambium (bottom) of 'Heritage'
red raspberry grown under high tunnel and field conditions in 2007-08. Vertical bars
indicate standard errors for individual means. Means containing two replications were:
field bud primordia on 27 Dec. and tunnel cambium on 8 Nov., 28 Nov., and 27 Dec. All
other means contained three replications ........................................................................ 98

Figure 3-5. Changes in percent dry weight of soluble carbohydrates (fructose, glucose,
sucrose, and raffinose), total soluble carbohydrates (sum of previous), starch, and total
nonstructural carbohydrates (starch + soluble carbohydrates) in the canes of red raspberry
cultivars grown under high tunnel and field conditions in 2007-08. Vertical bars indicate
standard errors for individual means ............................................................................... 99

Figure 3-6. Changes in percent dry weight of soluble carbohydrates (fi'uctose, glucose,
sucrose, and raffinose), total soluble carbohydrates (sum of previous), starch, and total
nonstructural carbohydrates (starch + soluble carbohydrates) in the canes of red raspberry
cultivars grown under high tunnel and field conditions in 2008. Vertical bars indicate
standard errors for individual means ............................................................................. 100

Figure 3-7. Changes in percent dry weight of soluble carbohydrates (fructose, glucose,
sucrose, and raffinose), total soluble carbohydrates (sum of previous), starch, and total
nonstructural carbohydrates (starch + soluble carbohydrates) in the canes of ‘Heritage’
red raspberry grown under high tunnel and field conditions in 2007-08. Vertical bars
indicate standard errors for individual means ............................................................... 103

Figure 3-8. Maximum and minimum ambient air temperatures at the Southwest Michigan
Research and Extension Center (SWMREC) in Benton Harbor, MI from 1 Aug. to 10
Nov. in 2008. Solid arrows indicate dates potted plants were moved outside of the high
tunnel. Dotted arrow indicates the date of cold hardiness sampling ............................ 107

xi

CHAPTER 1

REVIEW OF LITERATURE

Fresh Raspberry Production

Fresh raspberry consumption has increased considerably in the US. during the last two
decades. Per capita consumption of fresh raspberries in the United States was 0.37
pounds in 2007, a value over three times what it was in the early 19903 (USDA-ERS,
2009). Strong demand has kept the price of fresh raspberries high, encouraging greater
production for the fresh—market. In Oregon, fresh-market raspberry prices averaged twice
that of processing berries during 2001-2005 and in Washington, three times that of
processing during the same five year period (Pollack and Perez, 2006). One can quickly
observe that crop values are much larger when producing raspberries for the fresh-
market.

Michigan is one of the leading fi'uit producing states in the United States.
Michigan ranks fifth in the nation for the value of its fruit and prepared fruit products
exported internationally based on the state’s share of US. production in 2007 (USDA,
2008). Commercial red raspberry production is already occurring in the state with 500
acres under cultivation in 2006 (USDA, 2007). Michigan is in close proximity to many
large population centers such as Chicago and Detroit and has the potential to meet a

greater quantity of the demand for fresh raspberries in these population centers.

Growing raspberries in Michigan for the fresh market has several limitations.

Michigan summers are typically warm and humid with frequent rain. Diseases like grey

mold (Botrytis cinerea) and penicillium rot (Penicillium spp.) are increased by rain and
humid conditions where water on leaf surfaces evaporates slowly. Primocane-fluiting
(PF) raspberry cultivars (those that produce flowers on the current season’s shoots called
primocanes) fluit flom early August through the first killing flost in Michigan. Full
production ofien is not realized due to early flosts, and loss of fluit is common in
northern regions (Hoover et al., 1989). Floricane-fluiting (FF) raspberry cultivars
produce fruit on canes during their second season of growth. These cultivars do not fluit
at the time when fall frosts occur, but must be able to survive cold winter temperatures

since fluit is produced on a two-year-old cane.

Due to these limitations, Michigan flesh raspberries often lack the consistent
quality and volumes required to supply grocery store chains. Major raspberry growing
regions in the western United States, particularly California, have more consistent
weather conditions, less rain and humidity, and a longer growing season. Growers in
Michigan are beginning to adopt the use of a structure called a high tunnel to extend the
growing season and produce high quality raspberries with the potential to compete with

flesh raspberries flom California.

High Tunnels

The term high trmnel is used to describe a variety of structures that protect horticultural
crops. High tunnels can differ somewhat in size and shape although they share many
common characteristics (Lamont, 2009; Carey et al., 2009). High tunnels are hoop
houses with metal flames that are covered in a single layer of plastic. These structures

are large enough to allow for small equipment to enter flom the ends. High tunnels are

generally unheated and as such, plastic is placed on the ends and sides of tunnels in early
spring and late fall to trap heat accumulated during the day. During warm periods of the
year, plastic covering the ends of tunnels is removed and plastic along the sides is vented
to allow for air movement. Additionally, high tunnels lack a foundation and raspberry
plants are planted directly in the ground. High tunnels also do not typically have
electricity and are considered nonpermanent structures. As such, venting of the tunnel

plastic is done by hand.

Two categories of high tunnel structures exist: 4-season and 3-season structures.
A 4-season structure is often covered with plastic year round and is strong enough to
withstand heavy snow loads. Four-season structures usually have a peaked flame, cover
a smaller area per tunnel than 3-season structures, and single tunnels typically stand
alone. Research growing red raspberries and or blackberries under 4-season structures
has been conducted at the Penn. State High Tunnel Research and Education Facility
(Lamont et al., 2003; Demchak, 2009), Cornell University (Heidenreich et al., 2008),
Iowa State University (Domoto et al., 2007), and the University of Massachusetts

(Schloemann, 2007).

Three-season high tunnels differ flom 4-season in that plastic is removed during
the winter months. Plastic removal is necessary because the structure often has increased
distances between its structural supports and cannot support the weight of snow (Lang,
2009). The 3-season high tunnel has a rounded flame with vertical legs which can be
linked to form multi-bay units. Multi-bay structures can become quite large and cover

several acres. The dimensions of 3-season high tunnels range from 5.5 to 9 m (18 to 30

feet) wide, 3 to 4.5 m (10 to 15 feet) tall and lengths are designed to fit grower

specifications (Gaskell, 2004; Haygrove, 2009).

Research efforts using high tunnels to producte red raspberries are increasing.
Studies assessing yield under tunnels have been conducted in the United States as well as
abroad (Demchak, 2009). For instance, a multi-national project was started in 1993 in
which several European countries set out to determine proper agronomic management of
primocane-fluiting cultivars for winter production using tunnels in southern regions of
Europe (Rosati et al., 1999). Also, researchers in Belgium demonstrated season

extension potential for high tunnel raspberry production (Meesters and Pitsioudis, 1999).

Gaskell (2004) discussed the rise in protected agriculture in Southern California
during the early 19903. The author noted that off—season raspberry production under
protected structures in California occurred largely in San Diego, Ventura, and Santa
Barbara counties in 2004. Scientists at universities in the Northeast have been
conducting multi-year studies producing red raspberries in high tunnels (Lamont et al.,
2003; Heidenreich et al., 2008). A 2007 survey of extension agents across the US.
indicated that there were over 4,000 acres of raspberries under tunnels in California
(Carey et al., 2009). The survey also noted raspberries were grown as a tunnel crop in
other states such as Florida, Maine, Michigan, New Jersey, Oregon, Pennsylvania, Utah,

and Washington but in much smaller numbers than in California (Carey et al., 2009).
Economics

The economic feasibility of a high tunnel red raspberry production system is an

important consideration for a fruit grower. The venture must be profitable in order for a

grower to make the large high tunnel investment and for the operation to be sustainable.
Several economic analyses have been conducted for raspberry production in high turmels
(Heidenreich et al, 2008; Yan and Du, 2003) and in the field (Bolda et al., 2005;
Bushway et al., 2007). Bolda et al. (2005) composed a detailed extension publication
covering the costs to produce red raspberries in California; however, this analysis did not
incorporate high tunnel production. Moreover, the potential returns a grower can realize
in California are different flom those in Michigan. Yields in California are higher than in
Michigan because of a longer growing season, resulting in the potential to generate more
revenue per acre. Many of the costs associated with field production of raspberries can
be used in determining high tunnel expenses; however, additional expenses must be
considered for high tunnel production which include the cost of the structure, plastic, as

well as additional labor costs associated with the more intensive system.

The analysis conducted by Heidenreich et al. (2008) used 4-season high tunnels
with dimensions of 30 x 90 ft. (2,880 sq. ft.). These structures require space between
individual tunnels which results in unused land around the high tunnel structure. The
cost to’purchase one structure was $6,400, or over $2.00 per square foot. This is more
expensive than 3-season tunnels, which usually cost less than $1.00 per square foot,

depending on the size of the structure.

An economic analysis conducted in Ontario, Canada, investigated the financial
feasibility of producing raspberries under Haygrove (Ledbury, Herefordshire, UK) 3-
season high tunnels and greenhouses (Y an and Du, 2003). The net present value of the
cash flow for a one acre 3-season tunnel Operation was calculated to be $67,300 with an

internal rate of return equal to 34.9% considering a baseline interest rate of 5% (Y an and

5

Du, 2003). Net present value evaluates investments by considering opportunity costs of
using funds for capital items as well as the time value of money while internal rate of
return describes the interest rate relating the present value of cash inflows to outflows
(Boehlje and Eidman, 1984). The authors determined producing red raspberries under a
high tunnel system was practical and profitable. However, this information is not
completely applicable to Michigan growers. The capital costs included in the analysis

(Y an and Du, 2003) represented Canadian prices for goods. Capital costs were listed as a
lump sum; however, it would be beneficial to itemize costs so that growers can determine

for themselves what items are necessary for individual operations. The analysis also used

a standard yield estimate of 10,0001b-acre-1 for both PF and FF raspberries, not taking

into account yield differences between the two types. It currently is not clear whether
this level is realistic for Michigan producers. Studies in southwest Michigan indicate that
yields can be higher (Hanson et al., 2008). Also, flesh raspberry prices fluctuate
throughout the year as the supply of flesh raspbenies changes. A A distinction between
prices during harvest periods for FF and PF raspberries would be beneficial. An
additional economic analysis using current prices and yield data would be helpfirl to

growers considering 3-season high tunnel raspberry production in Michigan.
High Tunnel Benefits and Concerns

High tunnels offer a variety of benefits to raspberry producers. High tunnels
exclude rainfall and modify temperature, light quality, humidity, and wind around the
plant. Rainfall exclusion flom the raspberry canopy reduces the incidence of diseases

spread by water on both foliage and fluit. The duration of leaf wetness and temperature

have the greatest effect on producing Botrytis inoculum in strawberry (Legard et al.,
2000). The incidence of Botrytis and anthracnose was negligible on strawberry under
tunnels (Chandler et al., 2005), likely because of lower leaf wetness. Growers also can
use high tunnels to hasten or prolong harvest seasons by covering the sides and ends to
trap heat flom sunlight in the spring or late fall. Sealed high tunnels are warmer than
ambient temperatures during the day, causing raspberry plants to remain active longer in

the fall (Kadir et al., 2006).

Keeping raspberry plants active longer in the fall can be beneficial. Elevated
daytime temperatures under sealed high tunnels allow PF raspberry cultivars to produce
fluit longer in the fall, increasing yields and extending the growing season (Demchak,
2009). Canes of PF raspberry cultivars are not needed for fruit production the following

year and are pruned to the ground to allow new primocanes to emerge in the spring.

Management of FF raspberry cultivars differs flom that of PF cultivars.
Floricanes of FF cultivars are removed following harvest in late July and the remaining
primocanes continue growth. These primocanes initiate floral buds in their leaf axils in
response to short days and low temperatures in the fall (Williams, 1960) and buds must
overwinter before they emerge and flower. Extending the growing season and keeping
plants active longer in the fall could delay acclimation to fleezing temperatures in FF
raspberry plants (winter injury in PF cultivars is avoided by pruning). Conversely,
raspberry plants that remain active longer may accumulate more total carbohydrates.
Carbohydrate accumulation has been shown to increase the cold hardiness of other
woody species in some studies (Stergios and Howell, 1977) but not others (Wample and

Bary, 1992). Cold hardiness is defined as the ability of a plant to survive or resist

7

freezing temperatures (Fuchigami, 1996). The cold hardiness of FF raspberry canes
grown under a tunnel has yet to be studied in depth and only anecdotal comments
indicating improved plant survival under 4-season tunnels have been made (Heidenreich

et al., 2008).
Freezing Stress and Cold Hardiness

Woody plants in temperate climates experience seasonal stresses caused by fleezing
temperatures. Freezing stress sets the northern limits of raspberry production and
restricts the cultivars that can be grown. The process by which plants are damaged by

fleezing temperatures, remain uninjured, or are injured but recover is complex.
Mechanisms of Plant Injury by Freezing Temperatures

Freezing injury can be classified into several categories based on the location and
mechanism of injury in the plant: (1) primary direct fleezing injury, and (2) secondary
fleeze injury (Levitt, 1980). Primary direct freezing injury is the result of intracellular ice
crystal formation and is assumed to always be fatal (Levitt, 1980). Ice crystals formed in
cells cause damage to the protoplasmic structure possibly by puncturing membranes
(Levitt, 1980). When intracellular fleezing is very rapid (100°C s'1 or more) some cells
may survive because the ice crystals are extremely small; however, these rapid rates are

not typically found in nature (Levitt, 1980).

Secondary fi'eezing injury is caused by processes other than ice crystal formation.
An important form of secondary fleezing injury in deciduous woody plants results flom
extracellular fleezing. Ice that forms outside cells has a dehydrating effect on the

unflozen solution of the cell, increasing solute concentrations and lowering osmotic

8

potentials (Guy, 1990). Liquid water then moves out of the cell to the extracellular
solution or the ice crystal being formed (Guy, 1990; Sakai, 1982). The contents of cells
are then concentrated and cell volume reduced as liquid water leaves the cell. It is
hypothesized that extracellular fleezing can cause cell injury through cell volume
contraction, concentration of solutes, and possible pH changes (Steponkus, 1984);
however, concentration of cell solutes (Burke et al, 197 6) and cell dehydration (Ishikawa

and Sakai, 1981) are suggested to increase tolerance to fleezing temperatures as well.

Weiser (1970b) suggested that freezing injury in woody stems is not a continr'rous
process but occurs at specific temperature points. In controlled fleezing experiments
with woody plant material, as many as three exotherrns (points at which heat is given off
as water fleezes) were observed as temperature declined (W eiser, 1970b). The first
exotherm coincides with the extracellular fleezing of water. The second occurs as
protoplasmic water moves out of the cell in response to extracellular ice causing a vapor-
pressure deficit (W eiser, 1970b). The third exotherm is associated with the freezing of
protoplasmic constituents necessary for life, what Weiser termed as ‘vital water’, and
results in cell death. Exotherrns have been studied in a variety of woody species
including apple (Quamme et al., 1972; Quamme et al., 1973), grape (Pierquet and

Stushnofl‘, 1980), and blackberry and raspberry (W armund and George, 1990).
Freezing Resistance and Mechanisms of Plant Survival

The strategies which allow plants to survive fleezing stress can fit into one of two

categories: 1) fleezing avoidance and 2) fleezing tolerance (Levitt, 1980).

Freezing avoidance

Supercooling of plant tissue water is one method utilized by woody plants to
avoid fleezing temperatures. It is the result of plant temperature dropping below its
fleezing point without ice formation (Burke et al., 1976; Levitt, 1980). Flower bud
meristematic tissues of azalea, blueberry, apricot, cherry, and plum have been shown to
supercool (W eiser, 1970b; George et al., 1974; George and Burke, 1977). Wood ray
parenchyma cells of apple have also been shown to deep supercool down to temperatures
as low as -38° to -47°C (Quamme et al., 1973). The degree to which plant tissues can
supercool is limited since the lowest possible supercooling point for pure water is -3 8°C
in the absence of ice nucleators (Burke et al., 1976). Concentrations of aqueous solutions
likely to be found in plants have been shown to supercool to about -47°C (Rasmussen et
al., 1975; George and Burke, 1976). Supercooling is likely responsible for setting the
northern limit of production for several species in the Rosaceae family (apple and pear) in
North America (Quamme, 1976). It also has been found in a variety of other cultivated
fluit crops including apricot, blueberry, cherry, currant, grape, and raspberry (Quamme,

1995)

In supercooling tissues, ice crystals do not form even though temperatures fall
below the fleezing point of cellular water (Chen et al., 1994). In all freezing situations,
ice nucleation must take place in order for an ice crystal to form on or within a plant
(W isniewski et al., 2003). The process of converting water to a more stable state (ice) is
initiated by nucleation, or the first appearance of a very small volume of ice (V ali, 1995).
Ice nucleation can be either heterogeneous or homogeneous. Heterogeneous ice

nucleation takes place when small clusters of water molecules attach to a foreign surface,

10

a substrate, and the stability of that cluster is increased in response to having part of its
surface area attached to the substrate (V ali, 1995). Homogeneous ice nucleation occurs
without the presence of a substrate as water molecules spontaneously combine due to

reduced thermal motion (V ali, 1995).

Research has been conducted to investigate the control of ice nucleation events
on the plant surface, thus supercooling plants below 0°C to avoid fleezing (Lindow,
1995). The protein coat of certain bacteria are sites of ice nucleation (Hirano and Upper,
1995). The first release of a genetically modified organism for agricultural use was an
ice-nucleating active (INA) strain of bacteria (Pseudomonas syringae) where much of the
nucleation protein gene was deleted (Lindow, 1990). The resulting bacteria lacked ice
nucleation activity (non-INA) and were sprayed onto plants to compete with and reduce
the presence of INA bacteria thus reducing ice nucleation. Potato plants sprayed with
non-INA bacteria tolerated temperatures —2 to -5 °C to a greater extent than control plants

(Lindow, 1995).

Infrared (IR) video thermography has been used to visually determine points of
ice nucleation and propagation in plants (Fuller and Wisniewski, 1998; Ceccardi et al.,
1995). Using this technology, the heat of fusion released as water fleezes is imaged and
the location and timing of fleeze events in plant material can be determined. Workrnaster
et a1. (1999) demonstrated that in cranberry, water droplets containing ice-nucleating
bacteria would only fleeze if located on the abaxial side of leaves, providing evidence
that stomata are likely to facilitate ice propagation into plant leaves. A lag time existed
between when the droplet floze on the abaxial side of a cranberry leaf and when ice

would enter the leaf. The authors also noted that the adaxial cuticle may provide an

11

adequate barrier to ice propagation. Other possible entry points for extrinsic ice include
wounds, lenticels, and cracks in the cuticle while internal ice propagation is thought to

proceed through extracellular spaces and xylem vessels (Levitt, 1980).

Freezing tolerance

Freezing tolerance in plants can only be the result of extracellular freezing, as
intracellular freezing presumably disrupts cell membranes (Levitt, 1980). During
extracellular fleezing in plants, liquid water moves out of the cell to ice crystals forming
in extracellular spaces (Guy, 1990). Ishikawa and Sakai (1981) propose that during a
freezing event, the cell water of Rhododendron flower buds moves flom florets to ice
forming in the bud scales, increasing cell sap concentration and lowering the fleezing
point of the florets. Extracellular ice formation can be tolerated in plants if the
accompanying dehydration of cells can be avoided or tolerated (Chen, 1994). The
resistance of cell walls to collapse in some plants creates a negative pressure potential as
water moves toward extracellular ice, possibly decreasing cell dehydration during
extracellular fleezing (Rajashekar et al., 1982). The result of any dehydration of cells in
response to extracellular ice formation is the concentration of intracellular and

extracellular solutes (Steponkus, 1984).

Some researchers suspect that cold acclimation can be induced by plant
dehydration. The killing temperature of cells flozen extracellularly has been shown to
vary based on the cell’s ability to withstand fleeze-dehydration when cooled slowly
(Sakai, 1982). The promoters of several cold response genes are activated by both low

temperature and dehydration (Thomashow, 2001 ). Several genes that are induced by

12

water deficits in Arabidopsis seedlings as well as prior to seed desiccation may contribute

to fleezing tolerance (Thomashow, 1998).
Dormancy and Cold Hardiness in Woody Plants and Raspberry

Tissues of woody plants have the ability to adapt to seasonal changes. During late
summer and fall woody plants begin entering an inhibited state termed endodormancy
(Lang et al, 1987), or rest. During endodormancy, plant meristems cease visible growth
and buds will not open. Buds are released flom endodormancy following the
accumulation of a certain amount of time at low temperatures (Couvillon, 1995). The
number of hours needed at low temperature (chilling requirement) to overcome
endodormancy varies depending on plant species and cultivar. Estimates of the chilling
requirement for raspberry cultivars vary flom 250 to 780 hours (Dale, 2008). Dale et al.
(2003) suggests a model for calculating the number of chilling hours raspberry plants
accumulate using a weighted scale. Plants experiencing temperatures between 0 and 5.6
°C accumulate one chilling hour while temperature ranges slightly higher account for
fewer chilling hours and temperatures below 0 °C account for no chilling hours (Dale et
al., 2003; Richardson et al., 1974). In research conducted with primocane-fluiting
‘Heritage’ red raspberry, flowering was hastened by increasing the number of chilling
units (hours between 0 and 7 °C) (Takeda, 1993). Once the chilling requirement is met
and endodormancy is released, plant grth can commence when temperatures adequate

for growth occur. This state is called ecodorrnancy.

Raspberry plants also undergo processes during the winter dormant period that

increase their cold hardiness (Fuchigami, 1996). The dormant period can be divided into

13

three stages of cold hardiness: cold acclimation, mid-winter hardiness, and deacclimation
(Proebsting, 1970). Cold acclimation for woody perennials occurs in two phases. The
first is induced by photoperiod (Fuchigarni et al., 1970; Irving and Lanphear, 1967b; Van
Huystee et al., 1967) and the second by flost or low, non-fleezing temperatures (Howell

and Weiser, 1970; Gusta et al., 2005).

Photoperiod

Photoperiodic induction of cold acclimation is controlled by phytochrome

(McKenzie et al., 1974). Phytochrome exists in one of two photoreversible forms; Pfr or

Pr. PI is biologically inactive and absorbs red light, after which it is converted to Pfr. Pfi.

on the other hand, is the biologically active form, absorbs far red light, and is

subsequently converted to Pr (Smith, 2000). Additionally, Pfr can be slowly converted to

Pr during dark periods (Smith, 1995). It has been suggested that the ratio of Pfr to Pr

determines physiological responses in plants (McDonald, 2003).

In Cornus stolonr'fera, short days and end-of-day far red light treatment after long
days promotes growth cessation, cold acclimation, and increased cold hardiness in
response to low temperatures (McKenzie et al., 1974). Perception of light quality, the
relative amounts of red and far red light, occurs in plant leaves. Fuchigarni et al. (1971)
indicates that the short-day leaf is the source of a hardiness promoting factor and that it is
translocated through the phloem. Interestingly, photoperiod appears to have no effect on
cane height in the red raspberry cultivar ‘Autumn Bliss’ (Carew et al., 2003) and may

only minimally influence growth cessation in the fall if temperatures remain high. A

14

photoperiod response to short days can account for some increased cold hardiness during
the first stage of acclimation, however, low temperature plays a primary role in

increasing plant cold hardiness (Howell and Weiser, 1970).

Low temperature

The second stage of cold acclimation is brought about by low temperatures
(W eiser, 1970a; Gusta et al., 2005). Weiser (1970b) suggested that flost is the triggering
stimulus for the increase in cold hardiness. Temperatures of 0 to 5 °C induced greater
hardening than 5 to 10 °C (Levitt, 1980). Proebsting (1978) noted that subfleezing
temperatures greatly increased the cold resistance of dormant, acclimated woody plants.

It was shown in apple that low temperature alone can fully harden plants exposed only to

long days (Howell and Weiser, 1970).

Grth cessation is also noted as a prerequisite for cold acclimation (Fuchigami
et al., 1971); however, plants do not need to be physiologically dormant. Fast growing
raspberry cultivars have been shown to be more susceptible to flost injury in the fall than
slower growing cultivars (Van Adrichem, 1966). Several woody plant species have the
ability to cold acclimate as well as resume growth under favorable conditions (Irving and

Lanphear, 1967a).

Cessation of growth and development in red raspberry is an indicator of cold
hardiness. Early raspberry cane ripening (change in color) and early defoliation were
positively correlated with cold hardiness (Sako and Hiirsalmi, 1980). However, the
defoliation of raspberry canes must occur naturally. Doughty et al. (1972) showed that

canes of ‘Puyallup’ manually defoliated in early September displayed more damage after

15

fleezing tests during the winter than non-defoliated canes. Freeze damage was attributed
to a lack of photoperiodic induction as well as inadequate carbohydrate reserves. In
eastern thornless blackberry (Rubus sp.), premature defoliation appeared to decrease rrrid-

winter hardiness of stem tissue but had no effect on bud hardiness (Kraut et al., 1986).

Shoot growth in red raspberry requires both high temperature and long
photoperiods (Sonsteby and Heide, 2008). Growth of ‘Malling Promise’ occured
continually at 21 °C under short (9 h) and long (21 h) photoperiods, while at 15.5 °C
growth ceased under a 9 h photoperiod (Williams, 1959). Shoot lengths in early October
for ‘Glen Ample’ grown under natural day length were 85, 190, and 350 cm at 9, 15, and
21 °C, respectively and corresponding node numbers on the same day were 30, 45, and 80
(Sensteby and Heide, 2008). At 21 °C, growth slowed but continued into October when
the effective photoperiod was 11 h, although plants grown at 9 and 15 °C ceased growth
in September (Sonsteby and Heide, 2008). Temperatures of 18 °C were adequate to
maintain growth through 2 Nov. in ‘Glen Ample’ when the natural photoperiod was less
than 9 h (Sansteby and Heide, 2008). The critical photoperiod at 15 °C is 515 h to reduce
elongation growth and leaf formation in ‘Glen Ample’ (Sonsteby and Heide, 2008). The
previous research suggests that temperature plays a greater role in grth cessation than

photoperiod.

Methods to Evaluate Cold Hardiness

Early studies of cold hardiness in woody plants were based on field assessments
of plant growth during the following spring (Brierley et al, 1950; Van Adrichem, 1966;

Jennings and Carmichael, 1975). This method has been employed recently to compare

16

the cold hardiness raspberry of cultivars (Zatylny et a1, 1996; Hanson et al., 2005). While
field observations are non-destructive and straightforward, they vary with yearly weather
and may not give information about when fleeze injury occurred. Controlled-fleezing
tests have been used to simulate natural fleeze events (W olpert and Howell, 1985). Plant

tissues are placed in a fleezer and the temperature lowered at a consistent rate similar to

what occurs in the field (<5 °C hr-l) or as desired. Plant tissues are wrapped in aluminum

foil to facilitate even temperature distribution and prevent desiccation. Samples can also
be wrapped in moist cheesecloth to inoculate with ice and avoid supercooling if
warranted by the experiment. The temperature of specific tissues can be measured by
insertion of a thermocouple. The thawing rate after fleezing must also be standardized to

ensure unifOrmity.

To identify temperatures that cause injury, subsarnples are flozen to a range of
test temperatures. Five to nine test temperatures are typically selected and the range
between the temperatures varies with the species and time of year. The temperatures are
chosen so that no injury occurs at the warmest and all tissues are killed at the coldest.
This can be accomplished by removing subsarnples flom the fleezer once they reach the
predetermined test temperature and placing them into 0 to 5 °C conditions for

approximately 24 h.

A number of methods can be used to determine injury after fleezing stress
including regrowth tests (Cortell and Strik, 1997), tissue browning (Hummer et al., 1995;
Warmund et al., 1992), electrical conductance/resistance (Boorse et al., 1998), triphenyl

tetrazolium chloride (TT C) (Irving and Lanphear, 1968), differential thermal analysis

17

(DTA) (W arrnund et al., 1992; Ishikawa and Sakai, 1981), and chlorophyll fluorescence
(Stushnoff, 1972; J iang et al., 1999). The appropriate method to use depends on the plant

material to be tested and the objectives of the research.

Tissue browning is perhaps the most widely used method to evaluate cold
hardiness. Afier samples are frozen and thawed, they are placed in a humid chamber for
4-7 days at room temperature. During this time, fleeze-injured tissues develop a brown
color flom the oxidation of cellular contents which can be visually assessed by assigning
ratings to the degree of browning (W arrnund et al., 1986; Doughty et al., 1972) or using
values of alive and dead (Sterigos and Howell, 1973; Palonen and Lindén, 1999). This
method takes 1 to 2 weeks before results and is qualitative in nature, but is considered

reliable and uses minimal equipment (Stergios and Howell, 1973).

Cold hardiness was, at one time, reported in terms of percent kill at a given
temperature (Proebsting and F ogle, 1956). This made comparisons throughout a winter
difficult because a temperature appropriate during cold acclimation may be too warm to

kill sampled tissue during mid-winter. The temperature estimated to be lethal for 50% of

sampled tissue (LT50) has since been used to quantify and compare cold hardiness

(Bittenbender and Howell, 1974). LT50 can be calculated in a number of ways due to the

sigrnoidal shape of the temperature vs. survival curve. The Spearrnan-Karber method

(Bittenbender and Howell, 1974) as well as logit and probit models (Lindén et al., 1996)

can be used to estimate LT50.

18

Carbohydrates

Soluble carbohydrates are known to accumulate in woody plants during cold acclimation
and are positively correlated with cold hardiness (Ashworth et al., 1993; Hamman Jr. et
al., 1996; Palonen, 1999; Steponkus and Lanphear, 1968; Sakai and Yoshida, 1968).
Starch levels in woody plants have been negatively correlated with cold hardiness
(Jennings and Carmichael, 1975; Lasheen and Chaplin, 1971; Raese et al., 197 8). The
role of carbohydrates in cold hardiness is complex and although much research has been
conducted addressing the subject, direct relationships have not been well established

(Ashworth et al., 1993).

Soluble Carbohydrates

A variety of soluble carbohydrates occur in plants depending on the species, plant
tissue, environment, and developmental stage of the plant. Soluble carbohydrates found
in red raspberry plant tissue include sucrose, glucose, fructose, as well as minor amounts
of raffinose and stachyose (Palonen, 1999). The disaccharide sucrose is the major
soluble carbohydrate in raspberry tissue during the winter (Palonen, l 999; Kaurin et al.,
1981), and has been reported to be a more effective cryoprotectant than its
monosaccharide components glucose and fluctose (Crowe et al., 1990). Raffinose, a
trisaccharide composed of galactose, fructose, and glucose, has been correlated with
increased cold hardiness in Camus sericea, Lonicera caerulea, and F orsythia (Ashworth

et al., 1993; Flinn and Ashworth, 1995; Imarrishi et al., 1998).

Soluble carbohydrates may affect cold hardiness in different ways. Sugars lower

the fleezing point and increase the osmotic potential of cells. This could reduce the

19

amount of dehydration that occurs during extracellular freezing (Levitt, 1980). The
accumulation of low-molecular weight carbohydrates also appears to have a protective
effect on cell membranes (Santarius, 1973). Evidence suggests that sugars and sugar
alcohols act as colligative cryoprotectants for cell membranes and proteins by preventing
an increase in electrolyte and toxic compound concentrations that accumulate during
fleezing (Santarius, 1982). During fleezing stress, there is evidence that sucrose interacts
directly with the polar head groups of phospholipids in membranes and may replace
water by hydrogen binding to the polar heads (Crowe et al., 1987). Sakai and Yoshida
(1968) suggest that while the degree of freezing resistance is not explained by cell sugar
content alone, differences may be attributed to changes in the conformation of protein in

the plasma membrane and the degree to which sugars protect the membrane.

Soluble carbohydrates are correlated with cold hardiness in many plant species.
In the buds and rhizomes of Cloudberry (Rubus chamaemorus L.), cold hardiness is
positively correlated with the amount of soluble carbohydrates in tissues (Kaurin et al.,
1981). The author also states that sucrose content rose quickly after low temperature
exposure in the fall. Soluble carbohydrates were positively correlated with increased
cold hardiness in grape and it was found that leaving fluit on the vine did not
significantly affect soluble carbohydrate and starch reserves in bud or cane tissues
(W ample and Bary, 1992). Increases in the levels of sorbitol, a sugar alcohol, have been
associated with low temperature and cold hardiness in apple (Ichiki and Yarnaya, 1982).
Cold hardy shoots and flower buds of peach (Prunus persica L.) accumulate more soluble

sugars than tender ones as a percent of sample dry weight (Lasheen and Chaplin, 1971).

20

Several genetic studies indicate raffinose is related to the degree of cold hardiness
in herbaceous plants. Transgenic petunia plants were created with reduced activity of or-
galactosidase, an enzyme involved with the hydrolysis of raffinose during deacclimation.
These transgenic plants had much higher levels of raffinose and greater cold hardiness
than wildtype plants when exposed to acclimating temperatures (Pennycooke et al.,
2003). However, in Arabidopsis thaliana, increased raffinose levels did not influence
cold hardiness (Zuther et al., 2004). Mutants constitutively overexpressing galactinol
synthase as well as mutants lacking a raffinose synthase gene were used to study
raffinose levels and cold hardiness. Overexpressing galactinol synthase resulted in
greatly increased levels of raffinose. Mutants lacking raffinose were as cold hardy as
wild types or genotypes overexpressing galactinol synthase, indicating that raffinose is

not essential in basic freezing tolerance of A. thaliana (Zuther et al., 2004).

Despite the evidence that soluble carbohydrate levels are positively correlated
with cold hardiness in plant tissues, the relationship has not been shown to be causal. In
Hedera helix L. cv. Thomdale, both light- and dark-acclimated plants exhibited increased
cold hardiness; however, only the li ght-acclimated plants increased in sucrose levels
while dark-acclimated sucrose levels decreased (Steponkus and Lanphear, 1968). Sakai
and Yoshida (1968) found that poplar trees acclimated at 0 °C for two months had
dramatic increases in fleezing resistance accompanied by increased sugar levels.
However, trees acclimated at 15 °C had similar increases in freezing resistance but no

appreciable increase in sugar levels.

21

Starch

Soluble carbohydrates are known to accumulate in woody plants during cold
hardening as starch is hydrolyzed to low-molecular weight carbohydrates (Sakai and
Yoshida, 1968). Palonen (1999) reports that starch almost disappeared flom red
raspberry canes and entirely disappeared flom bud tissues during the winter months.
Keller and Loescher (1989) observed an apparent interconversion of starch and soluble
carbohydrates between November and January in shoot and trunk wood of sweet cherry.
While a decline in starch concentration may occur in overwintering plant tissues, it is not
always accompanied by increases in total soluble carbohydrate content (Steponkus and
Lanphear, 1968). Many authors indicate that soluble carbohydrates increase
simultaneously with the hydrolysis of starch (Alberdi et al. 1989; Ashworth et al., 1993;
Flinn and Ashworth, 1995), although it is unlikely hydrolysis of starch can account for

the full increase in soluble carbohydrates during cold acclimation.

Summary

Fruit growers in northern climates like Michigan are increasingly using high
tunnels to extend the growing season for raspberries and improve fruit quality. The
economic considerations of a high tunnel raspberry operation are of great importance for
growers of any size. Costs associated with production under 3-season high tunnels would
be expected to differ flom field production as well as 4-season structures due to modified
management practices and tunnel purchase. The potential markets for increased yields
under tunnels also must be taken into account, when investigating the profitability of a

high tunnel raspberry operation.

22

The cold hardiness of raspberry cultivars is also an important consideration in
northern climates. Red raspberry plants grown under 3-season high ttmnels remain active
longer in the fall if plastic is kept on late which may leave them more susceptible to cold
temperatures after plastic removal. Study of how raspberry cultivars acclimate to cold
temperatures under 3-season tunnels as well as understanding how removing plastic flom

the 3-season structure in the fall influences cold hardiness is necessary.

23

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33

CHAPTER II

THE ECONOMICS OF 3-SEASON HIGH TUNNEL RASPBERRY

PRODUCTION

Abstract
The potential profitability of raspberries under multi-bay 3-season high tunnels
(Haygrove Tunnels) was evaluated using yield data from studies in southwest Michigan,
adjusted costs for field raspberry production, and recent prices for flesh raspberries at the

Detroit Wholesale Market. Marketable yield for primocane-fluiting (PF) cultivars was

2,1001b-acre'1 in year 1 and 14,9001b-acre'1 thereafter, whereas yields of floricane-

fluiting (FF) cultivars were 1,7001b'acre.l in year 2 and 15,4001b-acre-l in years 3 and

following. Costs were estimated by modifying field production budgets and using
Michigan prices. Depreciation schedules assumed 3, 7, and 15 year life for the
polyethylene plastic, raspberry plants, and tunnel structures, respectively. Berry prices
were $3.90 and $4.80 per lb for FF and PF harvest seasons, respectively. These analyses
indicate that high tunnel raspberry production results in revenue above listed costs,
particularly for PP cultivars. However, some costs were not considered, such as land cost
and taxes, fluit cooling/ storage and transport to market, and labor recruitment, housing,
and management. Other risks/unknowns that need be considered are future raspberry
prices and competitiveness of Midwest-grown berries, longevity of raspberries under

tunnels, and unforeseen problems that may emerge with this new production system.

34

Introduction
High tunnel production of flesh red raspberries is increasing in the United States. Carey
et al. (2009) conducted a survey of US. extension agents in 2007 in which raspberries
were grown under tunnels in key fruit producing states such as Florida, Maine, Michigan,
New Jersey, Oregon, Pennsylvania, Utah, and Washington. California has the largest
acreage of high tunnels producing small fruit in the United States (Demchak, 2009), with

high tunnel raspberry production estimated at over 4,000 acres (Carey et al., 2009).

High tunnels are made in a variety of shapes and sizes, but share several common
characteristics: 1) structures are hoop houses with metal flames covered with a single
layer of plastic, 2) structures are large enough for small equipment to enter flom the
sides, 3) structures lack a foundation, 4) structures generally do not have electricity, 5)
considered nonpermanent structures, and 6) structures are generally unheated and plastic
is placed on the ends and sides in early spring and late fall to passively warm the tunnel
during the day. The warmer daytime temperatures increase the number of growing
degree days accumulated under high tunnels (Lang, 2009). Plastic is removed flom the
ends of tunnels during warm periods of the year and sides are vented to provide air

movement and heat dispersion.

High tunnels can be classified as either 4-season or 3-season structures. Four-
season structures have a peaked flame and tunnels are constructed individually. These
structures are often relatively small, ranging form 4.6 to 9.1 m wide by 18.3 to 29.3 m
long (Heidenreich et al., 2008; Lamont et al., 2003). The 4-season high tunnel is strong

enough to tolerate the weight of snow and will generally be covered in plastic year round.

35

Research conducted in Pennsylvania (Demchak, 2009), New York (Heidenreich et al.,
2008), Iowa (Domoto et al., 2007), and Massachusetts (Schloemann, 2007) demonstrated

that yields of raspberries or blackberries are higher under 4-season high tunnels.

Unlike 4-season high tunnels, the plastic of 3-season trmnels is removed in the
winter months. Increased distances between structural supports necessitate plastic
removal because the structure cannot support a heavy snow load (Lang, 2009). The 3-
season tunnel has a Quonset-shaped frame and vertical legs. Three-season trmnels also

form multi-bay units which can cover several acres.

Raspberry plants benefit flom the protected high tunnel environment. High
tunnels exclude rainfall flom the raspberry canopy, reducing the incidence of water-
dispersed disease on foliage and fluit. Grey mold (Botrytis cinerea) and penicillium rot
(Penicillium sp.) can be minimized when leaf and fluit surfaces remain dry (Legard et al.,
2000). High tunnels also alter light quality, humidity, wind, and temperature. Elevated
temperatures under sealed tunnels can extend the growing season for red raspberry plants

by as much as 3 to 4 weeks in the spring and the fall (Demchak, 2009).

Raspberry plantings have performed well under high tunnels (Demchak, 2009;
Hanson et al., 2008) although replicated experiments comparing yields between tunnel
and field environments are lacking. Yields and fluit quality of floricane-fluiting (FF) and
primocane-fruiting (PF) raspberries appear to be improved when produced under high
tunnels. Cultivars that are FF produce fluit flom July to early August under natural
conditions in the Northeast U.S. (Hanson et al., 2005; Weber et al., 2005b) on canes in

their second year of growth (floricanes). Canes of FF raspberries must overwinter before

36

they produce flower buds, resulting in no fluit production in the planting year. Cultivars
that are PF begin fruiting in August or September under natural conditions in the
Northeast U.S. (Hanson et al., 2005; Weber et al., 2005a; Goulart and Demchak, 1999)
on canes grown during the current season. Since PF cultivars fruit on current season’s

growth, they will produce some fluit the same year they are planted.

High tunnels are a large investment, making it important to determine if the
additional cost of the structure and associated management costs can be recovered.
Economic analyses of raspberry production have been conducted under field conditions
(Bolda et al., 2005; Bushway et al., 2007) and high tunnels (Heidenreich et al, 2008; Yan
and Du, 2003). Bushway et al. (2007) assembled a budget which listed the expenses for
each year associated with field production of a one acre bramble planting in the
Northeast. Profits flom one-acre commercial and pick-your-own summer raspberry
plantings were estimated at $4,660 and $2,200, respectively assuming yields of 2,000
pounds per acre. In a high tunnel raspberry production system, yields are likely to be
much higher. Additionally, the high tunnel structure and associated management costs
will change the potential income and profit that can be generated flom a one acre
planting, making it necessary to consider both a field and a high tunnel situation

separately.

Heidenreich et al. (2008) assembled a budget for producing PF raspberries using
4-season high tunnels with dimensions of 30 x 90 ft. (2,880 sq. ft). The cost of each
tunnel was $6,400; over $2.00 per square foot. The cost per square foot for 3-season
tunnels is less expensive at under $1.00 per square foot. Additionally, 4-season tunnels

require space between individual tunnels resulting in unused land. The authors predicted

37

that a single 4-season tunnel producing red raspberries would have a positive cash flow
afier four years with the first year being an establishment year having no revenue. They
assumed the raspberries would be sold for $3.00 per half pint. However, the analysis did
not consider differing yields prior to full production or differentiate between FF and PF

yields.

The economic feasibility of raspberry production with 3-season Haygrove
(Ledbury, Herefordshire, UK) high tunnels and greenhouses was conducted in Ontario,
Canada (Y an and Du, 2003). One acre of 3-season tunnel production had a net present
value of the cash flow of around $67,300. The internal rate of return was 35% using a
baseline interest rate of 5%, which the study notes is not realistic. The net present value
procedure is a method to evaluate investments which takes into account the opportunity
costs associated with having funds tied up in capital items as well as the time value of
money (Boehlje and Eidman, 1984). Internal rate of return describes the rate of discount
that equates the present value of the cash inflows with the cash outflows (Boehlje and
Eidman, 1984). This analysis showed that producing red raspberries could be profitable
under 3-season tunnels with the use of successful production and marketing systems.
Additional information could help growers in Michigan make better informed decisions
about investing in 3-season tunnels. Yan and Du, 2003 summarized capital costs instead
of itemizing them and considered Canadian prices for goods. Listing individual costs
would be beneficial for growers to determine what expenses are important for their
operation. A single estimate of 10,000 pounds per acre was used to approximate both FF
and PF raspberry yields. Studies in southwest Michigan indicate greater high tunnel

yields at full production for both raspberry types (Hanson et al., 2008).

38

The importance of considering the economics of raspberry production under high
tunnels for a fruit grower is undeniable. An additional economic analysis that uses
current costs associated with production of FF and PF raspberry types, specific yield data,
and wholesale raspberry prices would be helpful to growers considering 3-season high
tunnel raspberry production in Michigan. Consequently, the objective of the following
study was to estimate the potential profitability of 3-season high tunnel red raspberry

production in Michigan.

Materials and Methods
This study considered the scenario of a one-acre high tunnel operation producing either
FF or PF flesh red raspberries to be marketed wholesale. Haygrove (Ledbury,
Herefordshire, UK) 3-season high tunnels covered in Luminance THB plastic were used.
The costs of producing FF and PF raspberry cultivars under 3-season high tunnels in
Michigan were calculated, and wholesale raspberry prices calculated flom the Detroit
Terminal Market. This data was used to determine the break-even yield necessary to
cover costs and potential revenue flom one acre of high tunnel raspberries based on yield

data flom a replicated high tunnel raspberry planting.
Costs

The costs of producing FF and PF red raspberry cultivars on one acre were
calculated for each year in the 3-season high tunnel production system. Costs incurred
during the period prior to and at the time of planting were considered establishment costs
(Table 2-1). Since establishment costs would not occur again in the life of the planting,

they were summed and depreciated over the planting’s productive lifespan, estimated at 7

39

years. Prior to high tunnel construction, establishment costs for a high tunnel raspberry
planting will be the same as those for a field planting. Soil sampling, herbicide
applications, plowing and disking, fertilizer application, as well as ground cover planting
and incorporation the following spring were taken from Bushway et a1. (2007). The cost
of bare root raspberry plants was $1,950 ($0.715 per plant). Rooted plants were placed
0.6 m apart in rows on 2.4 m centers. It was assumed that 5 % of the plants would need
replacing the following year, costing approximately $90. The trellis and irrigation
purchase and installation costs were taken flom Bushway et al. (2007) and assumed to

remain in place for the life of the planting.

Production costs for years 1, 2, and 3-7 for a one acre high tunnel raspberry
planting are presented in tables 2-2, 2-3, and 2-4, respectively. Purchase of the one-acre
high tunnel structure ($30,000) and plastic ($6,500) were one time costs and were
depreciated over the lifespan of each item using the straight-line method (Boehlje and
Eidman, 1984) for which the purchase cost was divided by its expected life. Labor to
install the high tunnel (1600 h) was also depreciated. It was assumed that the high tunnel
structure would last 15 years, the plastic 3 years, and each asset would have no value

after these time periods. An interest rate of 8 % was charged on invested capital.

The remaining costs in Tables 2-2, 2-3 and 2-4 represent activities necessary to
produce one acre of red raspberries under high tunnels. All were calculated using
Michigan prices in 2008, except for irrigation which had previously been calculated by
Bushway et al. (2007) for field raspberry production. The costs taken flom Bushway et
a1. (2007) are for field raspberry production in the Northeast US. and would be similar to

costs in Michigan. Costs for pruning and harvest are specific to FF and PF raspberry

40

cultivars. Harvest laborers were paid a piece rate of $0.50 per 1/2 pint container. Other

labor costs were fixed at $10 per hour, which included base wages and payroll expenses.
Fruit were packed in half pint plastic clarnshell containers that hold 6 ounces of fruit
($0.145 per container) in cardboard flats holding 12 clarnshell containers ($0.50 per flat).

These packaging costs are listed under fixed and material costs (Tables 2-2, 2-3, and 2-4).

Production costs were also organized (Table 2-5) as fixed and variable annual
allocated costs at full production. Fixed and variable costs at full production were
determined as annual costs in order to calculate break-even yields. The cost of
bumblebees is $250 per year; however, FF cultivars lack flowers in year 1 and do not
need bumblebees. To account for this, the cost of bumblebees was depreciated over the

life of the planting for FF raspberry cultivars.

Yields

Expected yields were based on data from a trial of four FF and PF raspberry
varieties under high tunnels in southwest Michigan from 2005 to 2008 (Hanson et al,
2008). Average high tunnel yields of the two best FF cultivars (Encore and Nova) and
PF cultivars (Caroline and Heritage) in the second and third production years were used
to approximate full production for each type. Yield data was collected in 2008 to
determine the percent of the total yield for each cultivar that would be culled. Total
yields for all years were then reduced by 20% to account for cull fluit, resulting in an
estimate of flesh marketable yield. Fresh marketable yield at firll production for FF and
PF raspberries was estimated at 15,400 and 14,900 pounds per acre, respectively. Full

production was reached during different years after planting for FF and PF raspberry

41

cultivars and it became necessary to estimate flesh marketable yield for those years. The
flesh marketable yield of the two best FF cultivars (‘Encore’ and ‘Nova’) was 1,700 lbs
during the second year after planting and the two best PF cultivars (‘Caroline’ and
‘Heritage’) was 2,100 lbs in the fall of the planting year. Crop values were calculated for

each year after planting (Table 2-6).

Berry Prices

Expected berry prices were estimated flom recent flesh red raspberry prices at the
Detroit Terminal Market (USDA, 2008). The price data provided by the USDA are
prices received by wholesalers for sales of less than a carload or truckload of product
(USDA, 2009). While red raspberries arrive at the Detroit Terminal Market year round,
the periods that FF and PF raspberries grown in Michigan would be sold were estimated
flom high tunnel yield trials in southwest Michigan to be 22-June to 2-Aug (6 weeks) and
10—Aug to 31-Oct (12 weeks), respectively. The high and low price per flat (twelve, 6
ounce clarnshell containers) of red raspberries was recorded daily for fluit termed large.
An average of the high and low price per flat for fruit having a large size was calculated
for each day. These daily values were averaged for each selling period flom 2006-08 and
the average price per pound for FF and PF raspberry cultivars was calculated to be $3.90
and $4.80, respectively. These prices were estimates of what a grower could receive at
the Detroit Terminal Market and did not reflect the cost of transportation and handling of

fluit on its way to the market.

42

Wholesale raspberry volume

The shipping volume and place of origin for flesh red raspberries shipped to
wholesale markets in the United States are also available flom the USDA marketnews
website (USDA, 2008). Weekly volume totals for 2006-08 were summarized based on
their place of origin (Figure 2-1).

Break-even analysis

Break-even analysis was conducted using the following formula:

Fixed cost
Selling price per pound - Variable cost per pound

 

Break-even yield =

The break-even yield is the number of pounds of flesh marketable fluit necessary
to recover costs at full production. Prices for FF and PF raspberry types were considered
the selling price. Fixed costs were those listed in Table 2-5 that are independent of the
level of production. Variable cost per pound was the same for each raspberry type and
was calculated by dividing the labor and annual non-labor cost to harvest raspberries by
yield. The annual non-labor cost to harvest raspberries includes the cost of clarnshell
containers and cardboard flats. Variable cost per pound was $1.83.

Results and Discussion

Total fixed costs at full production for FF raspberry cultivars were greater than those for
PP cultivars (Table 2-5). Different pruning techniques made up the majority of the
difference in fixed costs between the two raspberry types. Pruning of FF raspberries
requires hand thinning of canes in the spring leaving 4 to 6 canes per linear foot of row as
well as removing spent floricanes at the end of harvest. Cultivars of PF raspberries were

assumed to be pruned once in the spring by hand removing all canes. In field plantings,

43

PF cultivars are typically mowed to the ground annually. A high tunnel production
system differs in that an extensive trellis is used to support canes which can become quite
tall. The cost to prune PF cultivars reflects hand pruning with a trellis in place. The cost
of removing spent floricanes for FF raspberry cultivars is the major pruning cost

difference between the two raspberry types.

Total variable costs differed for FF and PF raspberry cultivars (Table 2-5). A
slightly higher yield at full production for FF raspberry cultivars under high tunnels
(15,400 vs. 14,900 pounds per acre) increases harvest labor and packaging costs. As a
result of higher fixed and variable costs, FF raspberry cultivars at full production under
high tunnels were estimated to cost close to $4,800 per acre more to produce than PF

cultivars.

All costs were not considered in this study. Specific costs not included were land
values, property taxes and insurance, cooling facilities, marketing and shipping costs,
sanitation services (portable toilet and washing equipment), irrigation pump/well, and any
new buildings required. Cost assumptions were made considering a fluit grower wanting

to incorporate high tunnel raspberry production into an existing operation.

Costs of raspberry production under 3-season and 4-season high tunnels as well as
in a field setting are difficult to compare directly. Costs associated with management of a
9.1 m x 27.4 m, 4-season tunnel growing PF raspberries have been reported previously
(Heidenreich, 2008). The total labor and materials cost for one 4-season tunnel was
$9,500 (Heidenreich, 2008). Approximately 15, 4-season tunnels cover one acre of land.

Using the depreciation schedule described in the present analysis (15 year life, 8%

interest), the annual cost to cover an acre with 4-season tunnels was $15,550 compared to

$3,370 to cover an acre with 3-season high tunnels.

A number of other costs vary between 3- and 4-season tunnels. Irrigation can be
more efficiently constructed with long drip tapes under multi-bay, 3-season tunnels
compared to 15 individual 4-season trmnels. The design of 3—season tunnels allows for
increased labor efficiency. 'The ends of 3-season tunnels remain open during the growing
season while 4-season tunnels have doors that make removing pruned canes difficult.
Although plastic needs to be installed and removed annually for 3-season trmnels ($560
per acre), plastic remains on 4-season tunnels. However, Heidenreich et al. (2008) noted
that 4-season plastic needs to be retightened each year($600 per acre). Both tunnel types
need to be vented, but comparative labor costs are difficult to determine. Other costs
such as fertilization, pesticide applications, and purchase of pollinators might be similar

under 3- and 4-season tunnels.

Crop values at full production in the present analysis were greater for PF
raspberry cultivars ($71,520/acre) than FF ($60,060/acre), largely due to higher berry
prices during the PF harvest period (Table 2-6). Primocane-fluiting cultivars yield
around 600 pounds less than F F cultivars under tunnels but the higher fall berry prices
compensate for this reduced yield. An important aspect to consider with PF raspberry
cultivars is that the harvest season can be nearly twice as long as that of FF cultivars.
Daily or weekly fluit volumes are much lower for PF cultivars as a result. Fresh
raspberry prices increase as the PF harvest season progresses and the supply of flesh

raspberries is reduced.

45

Bushway et al. (2007) estimated that reasonable gross sales for field-grown FF
raspberries in the Northeast were between $8,000 and $12,000 per acre. This is well
below the calculated crop values for 3-season tunnel production of FF raspberries in the
present analysis ($60,060/acre). Heidenreich et al. (2008) estimated yields of PF
raspberries under a 4-season tunnel at firll production would be 4,000 half pint containers,
or about 22,500 lbs per acre. Using PF berry prices in the present analysis, 4-season
tunnels would have a crop value per acre of $108,000 at full production. It is apparent
that higher yields under 3- and 4-season tunnels result in higher crop values per acre than

field production.

Break-even yields were calculated in the present analysis for FF and PF
raspberries using a range of prices (Table 2-7 and Figure 2-2). Break-even yields were
lower in all price scenarios for PF raspberry cultivars than for FF. This is due to a lower
fixed cost incurred for PF cultivars since pruning took place once. Break-even yields are
below the estimated annual flesh marketable yields for FF and PF at full production
(Table 2-7) except when prices are near $2.00 per pound. When using estimated berry
prices flom the Detroit Terminal Market, the break-even yield was well below what has
been estimated for replicated high tunnel plantings (Hanson et al., 2008). These results
indicate that FF and PF cultivars would begin to generate revenue above the costs

included in the study when berry prices are at $2.72 and $2.49 per pound, respectively.

Raspberry prices change in response to supply and demand. Average price per
pound during harvest periods flom 2006-08 were used in this study, but there was
substantial fluctuation in prices between and within these years. Most flesh red

raspberries produced in the United States come flom California. California shipped

46

36,500 tons of flesh red raspberries in 2008, representing 49% of all flesh red raspberries
sold in the United States (Long and Maxwell, 2009). The remaining flesh red raspberries
were imported, largely flom Mexico and Chile during the US off season (Long and
Maxwell, 2009). Usual harvest dates for red raspberries in California are 10 May to 5
August (USDA, 2006). This time period overlaps the production season for FF raspberry
cultivars as well as the begimring of PF cultivars in Michigan. The supply of California
raspberries has a large influence on weekly prices. An increase in volume during the fall
would likely depress prices during the Michigan PF picking season. Future raspberry
prices cannot be predicted with certainty, but supply of fresh red raspberries during the
fall is increasing, which may result in lower prices in future years during this currently

profitable harvest window.

This study indicates that PF cultivars begin recovering investment costs earlier
than FF cultivars. Floricane-fruiting raspberries produce no fluit in the planting year
(year 1), have partial yield in year 2, and reach full production in year 3 (Table 2-6).
Primocane-fluiting raspberries have a partial yield in year 1 and reach full production in
year 2. No income is earned during year 1 for FF cultivars and costs will not be covered

by revenue.

Other risks should be considered before investing in high tunnels. It has been
observed that many disease and insect pests are reduced under tunnels, but additional
problems may develop over time. Plants in this study were estimated to remain healthy
and productive for seven years, but shorter or longer plant longevity would substantially
alter costs and revenues. Soils may require renovation with cover cropping or other

practices to prepare for replanting. This would add non-productive years to the replant

47

cycle. Fluctuations in the two largest costs in the analysis, labor and the high trmnel
structure, would change the profitability of raspberry production in this system. Steel
prices affect the cost of the high tunnel structure. Adequate labor availability is essential

for this labor-intensive enterprise.

The calculations for break-even yield in this analysis indicate that 3-season high
tunnel red raspberry production can be profitable above the costs in this analysis, with PF
cultivars being more profitable than FF. Crop value for PF cultivars was greater at full
production than for FF cultivars due to higher fall berry prices. Fresh marketable yield
was achieved during the planting year with PF cultivars while FF cultivars produced
marketable yield in their second year. Full production was estimated to be attained in
year 2 and year 3 for PP and FF cultivars, respectively. Break-even yields were lower for
PF raspberry types than for FF. Using berry price averages flom the Detroit Terminal
Market, break-even yields for both PF and FF raspberries were below observed yields
flom replicated trials, indicating revenue above costs. Several costs not considered in
this analysis included land values, property taxes and insurance, cooling facilities,
marketing and shipping, sanitation services, irrigation pump/well, and new buildings.
These costs need to be considered before investing in high tunnel raspberry production.

It is possible that some of the costs left out of the analysis could alter revenues enough to
noticeably increase the break-even yield. However, based on the costs and recent berry
prices used in this study, high tunnels are a promising technology for producing high

quality red raspberries in Michigan.

48

Literature Cited

Boehlje, MD. and V.R. Eidman. 1984. Farm Management. John Wiley & Sons, New
York.

Bolda, M., L. Tourte, K.M. Klonsky, and R.L. De Moura. 2005. Sample costs to produce
flesh market raspberries. Univ. Ca. Coop. Ext. Serv. Bul. RB-CC-OS
<http://coststudies.ucdavis.edu/files/raspberrvccO5.pdf>.

Bushway, L.J., M.P. Pritts, and DH. Handley. 2007. Budgeting. Chapter 14 In:
Raspberry and Blackberry Production Guide, 2nd Edition. Natural Resource, Agriculture

and Engineering Service (NRAES) Bulletin No. 35. Cornell Cooperative Extension,
Ithaca, NY.

Carey, E.E., L. Jett, W.J. Lamont Jr., T.T. Nennich, M.D. Orzolek, and K.A. Williams.
2009. Horticultural crop production in high tunnels in the United States: A snapshot.
HortTechnology 19:37-43.

Demchak, K. 2009. Small fluit production in high tunnels. HortTechnology 19:44-49.

Domoto, P., G. Nonnecke, L. Naeve, B. Havlovic, and D. Breach. 2008. High tunnel
bramble production. Iowa State University Research F arm Progress Report. ISRF08-12.
< http://wwwgiastate.edu/farms/O8reports/Armstrong/IflghTunnelBramble.pdf'>.

Goulart, BL. and K. Demchak. 1999. Performance of primocane fruiting red raspberries.
Fruit Var. J. 53:32-40.

Hanson, E., R. Issacs, A. Schilder, and M. Von Weihe. 2008. Tunnel culture of
raspberries in Michigan. Michigan State University web article

<ht_tp://www.maes.msu.edu/swmrec/publicationsfolder/Annualreports/OSannualgpt/Tunne
l%20RPT%20H_anson%2008£df>.

Hanson, E., S. Berkheimer, A. Schilder, R. Isaacs, and S. Kravchenko. 2005. Raspberry
variety performance in southern Michigan. HortTechnology 15:716-721.

Heidenreich, C., M. Pritts, M.J. Kelly, and K. Demchak. 2008. High tunnel raspberries
and blackberries. Cornell University, Dept. Hort. Pub]. No. 47.

Lamont, W.J., M.D. Orzolek, E.J. Holcomb, K. Demchak, E. Burkhart, L. White, and B
Dye. 2003. Production system for horticultural crops grown in the Penn State high tunnel.
HortTechnology 13:358-362.

Lang, GA. 2009. High tunnel tree fluit production: The final flontier? HortTechnology
19:50-55.

49

Legard, D.E., C.L. Xiao, J .C. Mertely, and CK. Chandler. 2000. Effects of plant spacing
and cultivar on incidence of Botrytis fluit rot in annual strawberry. Plant Disease 84:531-
538.

Long, T.C. and BE. Maxwell. 2009. Fresh fruit and vegetable shipments by
commodities, states, and months. USDA Agr. Mktg. Serv. FVAS-4 Calendar Year 2008.

Schloemann, S. 2007. High tunnel production of PrimeJim and PrimeJ an blackberries:
Progress report #1.
<http://www.umass.edu/fluitadvisor/pdf/NABGA2007Progresstt1b.pdf>.

US. Department of Agriculture Agricultural Marketing Service. 2008. Fruit and
vegetable market news report. <www.marl_<etnews.usda.gov/portal/fv>.

US. Department of Agriculture Agricultural Marketing Service. 2009. Fruit and
vegetable market news user guide.
<http://www.ams.usda.gov/AMSVI .O/getfile?dDocName=STELPRDC5048679>.

US. Department of Agriculture National Agricultural Statistics Service, 2006. Fruits and
Tree Nuts: blooming, harvesting, and marketing dates. Agricultural Handbook Number
729.p73.

Weber, C.A., K.E. Maloney, and J.C. Sanford. 2005a. Performance of eight primocane
fluiting red raspberry cultivars in New York. Small Fruits Rev. 4:41-47.

Weber, C.A., K.E. Maloney, and J .C. Sanford. 2005b. Performance of eleven floricane
fluiting red raspberry cultivars in New York. Small Fruits Rev. 4:49-56.

Yan, D. and C. Du. 2003. Economic feasibility analysis of raspberries under protective
structures in Ontario. MBA major paper, University of Guelph.

50

Table 2-1. Pro-plant and establishment costs associated with planting one acre of red
raspberries under 3-season high tunnels.

 

 

 

Depreciation
Fixed Material and zy
Activity Labor Costs Costs Total Interest

............................................. Y eer._l?.@r§.-rz£qaty_e.er2-_-_----._._._._-_._----._._._._._._._-_._._

Soil samples and tests (5 at $5.00 ea) $5 $45 $50 $9

Herbicide application $10 $5 $78 $93 $17

Plow field $20 $15 $3 $38 $7

Disc field $15 $25 $5 $45 $8

Fertilizer $10 $5 $83 $98 $18

Lime $10 $5 $103 $118 $22

Disc field $20 $15 $5 $40 $7

Harrow field $10 $10 $5 $25 $5

Plant ground cover $10 $5 $53 $68 $12
-lnsercetatseersr ............................... $.29._.-._.;$_1..5 _________ $.5. ......... $9. Q.-._._._--.§Z ....... _
Year! .................................................... _

Disc field $15 $25 $5 $45 $8

Lay out and stake rows $24 $26 $50 $9

Purchase and plant raspberries $950 $1,950 $2,900 $530

Pruchase and install trellis $350 $10 $1,005 $1,365 $250
-.I’Brsleé9_99<l.i_9§tsil.i.rslg§tjea-_._.__-.-._._.§1.2_9_.-_-.§.2_.5 ........ $.5_§§._._._.§.7_9_3. ......... t 13.9. .....
Yew ____________________________________________________ _

Replant (5%) $50 $90 $140 $26

Total $1,639 $160 $4,019 $5,818 $1,064

 

2
Interest rate = 8%

yDepreciated 7 years over the life of the raspberry planting

 

51

Table 2-2. Year 1 costs for producing one acre of red raspberries under 3-season high

 

 

trmnels.
13:;ng Depreciation;

Activity Labor Costs and Interest Total
Pro-plant and establishment costs $1,064 $1,064
Tunnel purchase and construction $3,371 $3,371
Purchase plastic (3 year life span) $2,427 $2,427
Install plastic $280 $280
Bumblebees $250 $250 pry
Irrigate $1 8 $214 $232
Fertilize $465 $465
Hand hoe/Weed $300 $300
Harvest (Piece rate $0.50 per 1/2 pt) $2,800 $1,045 $3,845 PF
Removeplasnc ._.§_2_§9 ...................................... _ ________ E .2339 ........
Total (PF) $3,678 $1,974 $6,862 P $12,514
Total (FF) $878 $679 $6,862 $8,419

 

 

 

 

 

2
Labor as well as fixed and materials cost is included in this figure

yPF = primocane-fluiting raspberry cost

 

52

Table 2-3. Year 2 costs for producing one acre of red raspberries under 3-season high tunnels.

 

 

Fixed and Depreciation
Material 2

Activity Labor Costs and Interest Total
Pro-plant and establishment costs $1 ,064 $1,064
Tunnel purchase and construction $3,371 $3,371
Purchase plastic (3 year life span) $2,427 $2,427
Install plastic $280 $280
Prune weak floricanes $1,200 $1,200 ”-1
Prune all floricanes $1,000 $15 $1,015 PFx
F ertilize $465 $465
Irrigate $18 $214 $232
Bumblebees $250 $250
Hand hoe/weed $300 $300
Harvest (Piece rate $0.50 per 1/2 pt) $2,267 $846 $3,113 FF
Spider mite spray $90 $61 $151
Prune spent floricanes $750 $750 FF
Harvest (Piece rate $0.50 per 1/2 pt) $19,867 $7,417 $27,284 PF
3399.29.99.89? ........................... _._§.2.89 ............................................... t {8.9 ........
Total (PF) $21,835 $8,422 $6,862 $37,119
Total (FF) $5,185 $1,836 $6,862 $13,883

 

 

 

 

 

2
Labor as well as fixed and materials cost is included in this figure

yFF = floricane-fruiting raspberry cost

x
PF = primocane-fluiting raspberry cost

 

53

Table 2-4. Year 3-7 costs for producing one acre of red raspberries under 3-season high

 

 

tunnels.
F133: 3:? Depreciation;

Activity Labor Costs and Interest Total
Pro-plant and establishment costs $1 ,064 $1,064
Tunnel purchase and construction $3,371 $3,371
Purchase plastic (3 year life span) $2,427 $2,427
Install plastic $280 $280
Prime weak floricanes $1,500 $1,500 1.13
Prune all floricanes $1,000 $15 $1,015 pp"
Fertilize $465 $465
Irrigate $1 8 $214 $232
Bumblebees $250 $250
Hand hoe/weed $300 $300
Harvest (Piece rate $0.50 per 1/2 pt) $20,534 $7,666 $28,199 FF
Spider mite spray $90 $61 $151
Prune spent floricanes $3,400 $3,400 FF
Harvest (Piece rate $0.50 per 1/2 pt) $19,867 $7,417 $27,284 PF
Ernsysrléais ............................. @389. .......................................... $.99. .......
Total (PF) $21,835 $8,422 $6,862 $37,119
Total (FF) $26,402 $8,656 $6,862 $41,919

 

 

 

 

 

2
Labor as well as fixed and materials cost is included in this figure

yFF = floricane-fluiting raspberry cost

x
PF = primocane-fruiting raspberry cost

 

54

Table 2-5. Annual allocated costs for producing one acre of red raspberries under 3-
season high tunnels at firll production.

 

 

 

 

 

Annual non-

Activity Labor labor costs Total
FIXED COSTS
Establishment costs depreciation and interestzy $300 $764 $1,064
High tunnel depreciation and interest $171 $3,200 $3,371
Plastic depreciation and interest $2,427 $2,427
Plastic installation $280 $280
Prune weak floricanes $1 ,500 $1,500 FF 1
Prune all floricanes $1,000 $15 $1,015 PFw
F ertilize $465 $465
Irrigate $18 $214 $232 FF
Bumblebees $250 $250 PF
Bumblebees $214 $214 FF
Hand hoe/weed $300 $300
Spider mite spray $90 $61 $151
Prune spent floricanes $3,400 $3,400 FF
13.19.899.1'emey91 ............................................ $ 2.33.0. ................................ S .239. .......
Total fixed costs (FF) $6,339 $7,381 $13,719
Total fixed costs (PF) $2,439 $7,396 $9,834
VARIABLE COSTS
Harvest (piece rate at $0.50/cont.) $20,534 $7,666 $28,199 FF
Harvest (piece rate at $0.50/cont.) $19,867 $7,417 $27,284 PF
TOTAL FIXED AND VARIABLE COSTS
Total (FF) $26,872 $15,047 $41,919
Total (PF) $22,305 $14,813 $37,118
2 Interest rate = 8%
Y

Annual land costs are not included in establishment costs
x
FF = Floricane-fluiting raspberry cost

w
PF = Primocane-fruiting raspberry cost

 

55

Table 2-6. Total allocated costs, marketable yield, and crop value flom one acre of
primocane-fruiting (PF) and floricane-fi'uiting (FF) raspberries under 3-season

high tunnels (F.O.B. farm).

 

 

 

Marketable yield
Costsz (lb/acre)y Crop valuex
Year PF FF PF FF PF FF
1 $12,510 $8,420 2,100 0 $10,080 $0
2 $37 , l 20 $13,880 14,900 1,700 $71,520 $6,630
3-7 $37,120 $41,920 14,900 15,400 $71,520 $60,060

 

2
Costs not included: land purchase and taxes, water, cooling/ storage facilities, marketing and
transportation, labor recruitment, housing, and management.

yEstimated flom yield trials at SWMREC minus 20% to account for cull fluit.

x
Based on PF and FF flesh raspberry prices of $4.80 and $3.90, respectively.

 

Table 2-7. Break-even yiele (lbs) for one acre of floricane-fluiting (FF)
and primocane-fluiting (PF) raspberries under 3-season high tunnel
production at various wholesale prices.

 

$3.00 $4.00 $5.00

 

FF:

$3.90y

PF: $4.80 $2.00
FF 6,630" 80,700
PF 3,310 57,850

11,730 6,320 4,330
8,410 4,530 3,100

 

Z .
Costs not included: land purchase and taxes, water, cooling/storage facilities, marketing,
labor recruitment, housing, and management.

yPrices are 3-year wholesale averages of Detroit Terminal Market prices during harvest

periods for FF and PF raspberries.

x
Break-even yields represent the necessary annual yield to break even and are calculated
by the following formula: annual fixed cost / (selling cost - variable cost)

56

 

 

 

 

 

 

 

    

 

 

6
0
0
2
m h v , I’ll/llllllllll/a
I .1 II///////// I’ll/Ill/I/lla
m w IIVJ/r/IZ. It’ll/I’ll
C S
. _
.m .m
m m m
m m m m
a a h
C C C M

a
— m

7
- J Ar

0

m m o m
8 6 4 2

 

@5255 .5 as:

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Date

Figure 2-1. Number of flats (in thousands) of twelve, 6 oz clarnshell containers of flesh
red raspberries shipped in the United States flom 2006-08. Stacked bars represent

volumes and their place of origin (California-Central, California-South, Chile, and

Mexico). Data compiled by Laura Havenga.

57

 

+ Floricane-fruiting (FF)
90000 ‘ —0- Primocane-fruiting (PF)

80000 a

 

 

70000-

60000“

50000 -

40000 a

Break-even yield (lbs.)

30000 -

20000 -

10000 4

 

 

 

O I I I I I I I

1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50
Berry price ($/lb)
Figure 2-2. Break-even yield (lbs) for one acre of floricane-fruiting (FF) and primocane-
fluiting (PF) raspberries under 3-season high tunnel production at various wholesale

prices. Arrows indicate average prices flom the Detroit Terminal Market during harvest
periods for FF ($3.90/lb) and PF ($4.80/lb) raspberries from 2006-08.

58

CHAPTER 3

COLD HARDINESS AND CARBOHYDRATE COMPOSITION OF RED
RASPBERRY (Rubus idaeus L.) GROWN UNDER 3-SEASON HIGH TUNNEL

AND FIELD CONDITIONS

Abstract

High tunnels alter the microclimate around plants of red raspberry (Rubus idaeus L.) and
influence many aspects of growth. If cold acclimation is inhibited, raspberry plants may

be damaged by early fall fleezes. This study investigated cold acclimation of raspberry

plant tissues grown in 3-season high tunnels. Cold hardiness (LT50) and nonstructural

carbohydrate concentration were determined in three floricane-fluiting (FF) red raspberry
cultivars during cold acclimation under high tunnel and field conditions for two growing
seasons. Bud primordia and cambium tissues of ‘Nova’ were typically more hardy than
those of ‘Canby’ or ‘Encore’. Soluble carbohydrates (fluctose, glucose, sucrose, and
raffinose) in canes were positively correlated with cambium cold hardiness while starch
was negatively correlated with hardiness. Raffinose concentrations were higher in canes
of ‘Nova’ than in ‘Canby’ on all sampling dates for field canes. Removing high tunnel
plastic after FF cultivars finished fluiting had no effect on cambium cold hardiness but
slightly increased early November hardiness in bud primordia. High tunnel environments
did not strongly affect the cold hardiness of bud primordia and cambium tissues during

cold acclimation or affect maximum winter hardiness levels.

59

 

Introduction

Horticultural crop producers in the Midwest and Northeastern U. S. are increasingly
becoming interested in high tunnel technology to produce red raspberries. High tunnels
differ in size and shape but they are typically defined as unheated hoop houses covered in
a single layer of plastic. Tunnels can be warmed during the day in spring and fall by
covering the ends and sides with plastic. In warm parts of the year, ends and sides are
removed and plastic covering the top of the structure is vented to release heat. High

tunnels lack foundations and crops are often planted directly into the ground.

High tunnels are often described as 4-season or 3-season structures. A 4-season
high tunnel is covered with plastic year round while a 3-season high tunnel must have its
plastic removed during the winter because it cannot support heavy snow loads (Lang,
2009). A common type of 3-season tunnel forms multi-bay units and covers multiple
acres while 4-season tunnels are single bay units and cover smaller areas. A 4-season
tunnel costs over $2.00 per square foot to purchase (Heidenreich et al., 2008) where a 3-

season high tunnel is often under $1.00 per square foot.

High tunnels modify plant microclimate by excluding rainfall and modifying
temperature, light quality, wind, and humidity. The incidence of water-dispersed disease
on foliage and fluit is reduced by keeping rain off the raspberry canopy. The occurrence
of grey mold (Botrytis cinerea) and penicillium rot (Penicillium sp.) is minimized when
leaf and fluit surfaces are not wet for extended periods (Legard et al., 2000). A major
benefit of raspberry production under high tunnels is that the growing season can be

extended by as much as 3 to 4 weeks in the spring and fall (Demchak, 2009; Meesters

60

 

and Pitsioudis, 1999). The number of growing degree days accumulated under high
tunnels is increased because of elevated daytime temperatures (Lang, 2009), particularly
if tunnel ends and sides are sealed in the spring and fall. High tunnels have been
increasing in use since the early I990S (Gaskell, 2004; Carey et al., 2009) and berry
production under plastic tunnels is projected to increase in the future (Carlen and Kriiger,

2009)

The modified environment under high tunnels can hasten growth of raspberry
plants in the spring and prolong it in the fall. Floricane-fluiting (FF) raspberries produce
fluit during July and early August in Michigan (Hansen et al., 2005) on canes in their
second year of growth. Primocane-fluiting (PF) red raspberry cultivars produce fluit
flom mid-August through the first killing flost in Michigan (Hanson et al., 2005) on
canes in their first year of growth (primocanes). The prolonged physiological activity of
PF raspberry cultivars in the fall under sealed 3-season high tunnels allows them to

continue producing fluit longer than otherwise possible.

After the harvest of FF raspberries concludes in early August (Hanson et al.,
2009), floricanes senesce and primocanes continue growth until they enter
endodormancy. Plant meristems cease visible growth and buds fail to open under
weather conditions favorable for growth during endodormancy. Meristems are released
flom endodormancy after remaining at low temperatures for an adequate amount of time
which varies by species and cultivar (Couvillon, 1995). The number of hours required to
release raspberry plants from endodormancy ranges flom 250 and 780 hours depending

on the cultivar (Dale et al., 2003; Dale, 2008).

61

The induction of endodormancy in red raspberry is controlled by temperature and
photoperiod (Sonsteby and Heide, 2008). Continual growth occurs at 21°C under short (9
h) and long (21 h) photoperiods in ‘Malling Promise’ red raspberry, but growth ceases at
15.5 °C under a 9 h photoperiod (Williams, 1959). Growth at 21 °C is slowed but
continuous in ‘Glen Ample’ into October where the photoperiod was 11 h (Sonsteby and
Heide, 2008), suggesting higher temperatures negate the effect photoperiod has on

inducing endodormancy.

Raspberry plants also undergo a transition concomitantly with endodormancy in
which tolerance of freezing temperatures increases, a process called cold acclimation.
Cold acclimation of woody plants occurs in two phases. Photoperiod initiates the first
phase (Fuchigami et al., 1970; Irving and Lanphear, 1967; Van Huystee et al., 1967)
while the second is induced by low, non-fleezing temperatures or flost (Howell and

Weiser, 1970; Gusta et al., 2005).

Cold hardiness is defined as the ability of plants to survive freezing temperatures

(Fuchigami, 1996) and is commonly expressed as LT50, or the temperature at which 50%

of tissue is estimated to be killed (Levitt, 1980). The Spearman-Karber method

(Bittenbender and Howell, 1974) as well as logit and probit models (Lindén et al., 1996)

can be used to estimate LT50.

Growth cessation is a prerequisite for cold acclimation in woody plants
(Fuchigami et al., 1971) and early growth cessation has been associated with greater
winter survival of raspberry canes (Fejer, 1973; Van Adrichem, 1966 and 1970). Early

raspberry cane “ripening” (change in color) and early natural leaf senescence were

62

positively correlated with hardiness (Sako and Hiirsalrrri, 1980). However, premature
defoliation appears to reduce hardiness. Canes that were manually defoliated in early
September were less hardy than naturally defoliated canes during the winter (Doughty et
al., 1972). Starch and sugar content of raspberry canes were reduced when defoliated by
two-spotted spider mite (Doughty et al., 1972). In eastern thornless blackberry (Rubus
sp.), premature defoliation appeared to decrease mid-winter hardiness of stem tissue but

not buds (Kraut et al., 1986).

Anecdotal evidence indicates that 4-season high tunnel use allows FF cultivars
that are considered to be less hardy to overwinter in climates where they would otherwise
be killed (Heidenreich et al., 2008). Research indicating if better overwintering is due to
increased plant cold hardiness or protection flom harsh winter conditions under the 4-
season high tunnel is lacking. The carbohydrate status of overwintering plants plays an
essential role in their ability to survive fleezing temperatures. Overwintering tissues such
as shoots, buds, and roots become sinks and must contain sufficient carbohydrates to
survive winter and resume growth the following spring. Plant carbohydrate status can be
influenced by various cultural practices (Howell, 1988). Reducing carbohydrate supply
by manual defoliation reduced cold hardiness in raspberry (Doughty et al., 1972;
Jennings and Cormack, 1969), tart cherry (Howell and Stackhouse, 1973), and grapevines

(Mansfield and Howell, 1981; Stergios and Howell, 1977).

Relative levels of carbohydrates change as plants acclimate to cold. Soluble
carbohydrate levels increase in acclimating raspberries (Palonen, 1999) and other woody
plants (Ashworth et al., 1993; Hamman Jr. et al., 1996; Steponkus and Lanphear, 1968;

Sakai and Yoshida, 1968). Red raspberry plant tissues contain the following soluble

63

carbohydrates: sucrose, glucose, fluctose, and low concentrations of raffinose and
stachyose (Palonen, 1999). The soluble carbohydrate in greatest concentration during
winter is the disaccharide sucrose (Palonen,1999; Kaurin et al., 1981). Sucrose is
composed of the monosaccharides glucose and fluctose and was noted as a more
effective cryoprotectant (Crowe et al., 1990). Galactose, fluctose, and glucose, form the
trisaccharide raflinose which has been associated with greater cold hardiness in Camus
sericea, Lonicera caerulea, and F arsythia (Ashworth et al., 1993; Flinn and Ashworth,
1995; Irnanishi et al., 1998). Starch concentrations in raspberry plant tissues have been

shown to be negatively correlated with hardiness (Palonen, 1999).

The effect of high tunnels on cold acclimation and hardiness of PF raspberry
cultivars is normally not a concern because canes are pruned to the ground each spring.
However, the effect of modified tunnel environments on cold acclimation of FF raspberry
canes that must overwinter has not been studied. Elevated tunnel temperatures may cause
plants to grow later in the fall, possibly increasing storage carbohydrate reserves but
delaying the cold acclimation process. Since FF raspberry cultivars finish fluiting by
early August, high tunnel plastic is no longer needed to protect fluit after this time and
could be removed. Removing plastic after harvest may promote growth cessation and

cold acclimation of canes.

The objectives of this investigation were to characterize the acclimation pattern of
red raspberry plants grown under a high tunnel in contrast to a field environment and
understand how the timing of high tunnel plastic removal affects acclimation.
Carbohydrate level changes occurring concomitantly with cold acclimation of plants

grown under 3-season high trmnels was also investigated.

64

Materials and Methods

High tunnel and field cultivar comparisons

An eight bay range of 3-season high tunnels (Haygrove Ltd., Ledbury, UK) were erected
at the Southwest Michigan Research and Extension Center (SWMREC) in Benton
Harbor, Michigan (latitude = 40.09 N, longitude = 86.36) in the spring of 2005. Each
high tunnel bay measured 7.3 m x 61.0 m, was 3.8 m high, and was oriented north to
south. Various raspberry cultivars were planted in one tunnel bay during May 2005 in a
randomized complete block design with three blocks. Raspberries were planted in plots
containing three plants with a between plant spacing of 1.3 m and rows on 2.4 111 centers.
The same RCBD layout was also duplicated in an adjacent field site with blocks oriented

east to west. However, the field layout differed in that rows were on 3.0 m centers.

Trials included four cultivars (‘Canby’, ‘Encore’, ‘Heritage’, and ‘Nova’) pruned
for floricane fruit production by removing floricanes after fruiting in the summer and
thinning floricanes each spring to approximately 20 canes per linear meter of row. Plants
were irrigated daily throughout the growing season and fertigated one or two times per

week with a total of 19 L of 4N-0P-8K liquid fertilizer on a Spinks loamy fine sand soil.
The rate applied is roughly equivalent to 224 kg N-ha-l. No fungicides or pesticides were

used in the high tunnel or field plantings until 11 Jul. 2008 when an application of

Acramite was applied to both plantings to reduce two-spotted spider mite populations.

Maximum and minimum outside air temperatures were recorded at 1.5 m height
flom the SWMREC/MAWN (www.agweather.geo.msu.edu/mawn/station.asp?id=swm)
weather station (Campbell Scientific, Logan, Utah) less than 200 m from the high tunnel.

65

 

Temperatures inside the high trmnel were measured flom 8 Aug. to 8 Oct. 2008 using 3
data loggers (HOBO U10-003; Onset Computer Co., Boume, Mass.) at 1.5 m height.
Data loggers were spaced equidistant down the center of the high tunnel with established
raspberry plants and were within the raspberry canopy at this time. High tunnel
temperatures flom 10 Oct. to 29 Oct. 2008 were recorded using 3 data loggers in another
high tunnel at 1.4 m height above the raspberry canopy. Temperatures flom the data
loggers as well as flom the weather station were converted to growing degree days

(GDD) using a base temperature of 10 °C (Baskerville and Emin, 1969).

Cold hardiness determination. During the fall and winter of 2007-08 and the fall of
2008, experiments were conducted using three FF cultivars (‘Canby’, ‘Encore’, and
‘Nova’) to evaluate cold hardiness in a high tunnel and field environment. Samples were
collected during the first winter season on 8 Nov. 2007, 18 Jan., and 14 Mar. 2008.
Sampling dates during the second season were 30 Oct., 13 and 29 Nov., 6, 26, and 29
Dec. 2008. Tissues were sampled flom the tunnel and field on the same dates except in
one instance when samples were collected three days earlier from the field (26 Dec.
2008) than the tunnel (29 Dec. 2008), due to time constraints. A more detailed time
course sampling was conducted using ‘Heritage’ pruned to fluit on floricanes to observe
changes in hardiness over an entire dormant season. Samples of ‘Heritage’ were
collected on 8 and 28 Nov., and 27 Dec. 2007 as well as 18 Jan., 22 Feb., and 14 Mar.

2008.

Whole cane samples, ranging flom two to five canes per plot, were collected the
morning of each sampling date. It became necessary to collect more than two canes at

later sampling dates in field plots in order to have adequate tissue. Samples were driven

66

 

to East Lansing, MI within 2.5 h after collection. Field canes sampled on 26 Dec. 2008
were collected in the afternoon and not in the morning. Cane samples were kept cool in

the bed of a pickup truck with a topper or inside a vehicle with air conditioning.

Once in East Lansing, samples were placed in a 4 °C cooler. Samples were
prepared for controlled freezing in order of replication. The apical portion of each cane
was removed near 0.6 cm diameter or below the lowest fluiting lateral if present. The
basal portion of each cane was removed as well, totaling 13 to 20 nodes. The middle 1%

section of each cane was divided into segments with two healthy buds.

 

The controlled fleezing procedure was similar to that done by Wolpert and
Howell (1985). Eight two-node segments of each cultivar replication were spaced 5 cm
apart and secured between two pieces of masking tape. F our of the segments were
tunnel-grown canes of a single cultivar and four were field-grown. Each eight-segment
group was then wrapped in moist cheesecloth to avoid supercooling and cause ice
nucleation (McKenzie and Weiser, 1975), then wrapped in aluminum foil. A 40-guage
copper-constantan thermocouple was inserted into the pith of one segment to measure
temperature. The foil was then rolled into a loose bundle. For each cultivar x replicate
combination, a total of five, six, or seven bundles were prepared to be flozen to five, six,
or seven test temperatures. Temperatures were selected based on the time of year so that
the warmest would cause no damage and the coldest would kill all test tissues. Bundles

were placed in a programmable fleezer, arranged by replication, allowed to equilibrate to

0 °C, and then cooled at 3 °c h".

67

When bundles reached the desired temperature, they were removed and placed in
a 4 °C cooler to thaw overnight. The next day, the foil, cheesecloth, and thermocouples
were removed and cane segments were placed in a humid chamber at 18 °C for four to
seven days to induce oxidative browning of damaged tissues. Bud primordia and
cambium tissues were then evaluated visually for injury based on the level of oxidative
browning (Stergios and Howell, 1973). Bud primordia were rated alive or dead, while
cambium tissue was rated alive, undistinguishable, or dead. Ratings flom each

replication were used to calculate the temperature at which 50% of sampled tissue was

estimated to be killed (LT50). LT50s were estimated using logit models (Lindén et al.,

1996) in the PROBIT procedure (SAS Institute, Cary, NC).

Carbohydrate determination. Cane tissue was collected for carbohydrate
analysis at all cold hardiness experiment dates, as well as on 14 Aug. 2008. Three 20 to
30 mm thick cross-sectional pieces were collected flom the upper, middle, and lower
portions of the central section of each cane used in the controlled freezing experiments.
Cane sections were stored at -80 °C and later lyophilized and ground to pass through a

40-mesh screen.

Lyophilized, ground samples weighing 100 mg were extracted three times with
2.0 mL 80% (v/v) ethanol for 30 min followed by 5 min centrifirgation at 3000 rpm.
During each extraction, samples were placed in a 60 °C hot water bath. Supernatants
were collected and evaporated to dryness (Savant Speedvac SC200) and stored over

desiccant prior to analysis. Pellets were frozen for later starch analysis.

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To determine soluble carbohydrates, samples were re-suspended by adding 2.0

mL of an oximation solution containing 10 mg-mL'1 hydroxylamine hydrochloride and

2.5 mg-mL-1 B-phenyl-D-glucopyranoside brought to volume with pyridine. Samples

were capped, agitated on a shaker tray overnight to dissolve carbohydrates, placed in an
80 °C heat block for 1 h, and allowed to cool to room temperature. Oximes and sugars
were converted to trimethylsilyl derivatives by adding 1.0 mL hexarnethyldisilazane
(HMDS) and 0.1 mL trifluoroacetic acid (TFAA). Samples were held at room
temperature for 1 h, then transferred to vials and analyzed by gas-liquid chromatography
(Aligent Technologies 6890N). Peaks for soluble carbohydrates were identified based on
retention times and compared to sugar standards (glucose, fluctose, inositol, sucrose, and

raffrnose). Peak areas were converted to percent of sample dry weight.

Pellets flom extracted samples were used for starch determination. .To each dry
pellet, 2.0 mL of 0.1M pH 5.0 acetate buffer was added. Samples were placed in a 100
°C hot water bath for 1 h. Upon hot water bath removal, 100 11L of arnyloglucosidase
flom Aspergillus niger (Sigma Chemical 10115) having 10 units of activity was added

and samples were placed into a 55 °C hot water bath for 16 h. After centrifugation, a 50
uL aliquot transferred to a new test tube and brought to 1.0 mL volume with ddHZO.

Triplicate 250 11L aliquots of sample flom the new test tubes were incubated for

approximately 1 h in 2.0 mL of a reaction mixture containing 12.8 unitsmL'1 of glucose
oxidase, 2.6 units-mL-1 of peroxidase, and 3.1 ug-mL-1 of o-dianisidine dihydrochloride.

The reaction was stopped by the addition of 2.0 mL of 12 N H2SO4. Samples were

69

analyzed spectrophotomerically at 540 nm using a BioSpec-1601 (Shimadzu Scientific

Inst., Japan).
Potted raspberry experiment

To study plastic removal date effects on cold hardiness, potted raspberry plants were
removed flom a tunnel on different dates in the fall to simulate the removal of high tunnel
plastic Bare root cuttings of three FF red raspberry cultivars (‘Canby’, ’Encore’, and
‘Nova’) were potted on 17 Apr. 2008 in East Lansing, MI. Two bare root cuttings of
each cultivar were planted in # 5 Nursery Supply pots containing 14 L of a standard
nursery potting substrate (80% pine bark screened to pass a one-inch grid, 20% Canadian
sphagnurn peat mass, 454 g of granulated sulfirr per cubic yard). Potted raspberries were
placed in a greenhouse for one week to accelerate growth, then transported to SWMREC.

Cuttings were pruned to the lowest above ground node to encourage primocane growth.

Potted raspberries were placed under one of the high tunnels described earlier.
Pots were arranged randomly in three-pot groups so that every group contained one pot of
each cultivar. The groups were placed into socket pots buried in the ground 0.46 m apart

in a row down the length of the high tunnel starting 12.2 m away flom either end.

Each three-pot group was randomly assigned one of four high tunnel removal
dates (14 Aug, 11 Sept, 9 Oct., 6 Nov. 2008 (not removed)), when pots were moved to a
second row of socket pots outside the tunnel with the same pot spacing and order. Pots
were removed from the tunnel to simulate removal of high tunnel plastic at different
dates. Each treatment (cultivar x removal date) was represented by six pots, with two

pots serving as one replication.

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Raspberries were irrigated for approximately 1 h-d-1 using 3.8 L-h-l micro

emitters placed in each pot and top dressed with Harrell’s Inc. Polyon® Acid Blend with
Micros (l9N-2.6P-9.9K) at 88 g per pot on 30 Apr. 2008. Substrate pH was monitored

during the growing season but did not need adjustment.

On 6 Nov. 2008, all raspberry canes with a base diameter larger than

approximately 1 cm were collected flom each treatment to evaluate cold hardiness as

described above, except the fleezer temperature was lowered at 2 °C h-l. The lower rate
was selected to account for the larger number of foil bundles in the fleezer ensuring a

similar fleezing rate in all bundles. Carbohydrate determination was conducted as

described previously.

Statistical analysis. The high tunnel and field cultivar comparisons experiment was
arranged in a randomized complete block design in a high tunnel and field setting, while

the potted raspberry experiment was a 2-way factorial design. Statistical analyses in both

experiments were performed for LT50 as well as individual and total soluble

carbohydrates, starch, and total nonstructural carbohydrates (total soluble carbohydrates
+ starch) using percent dry weight values. Mean separation between cultivars was carried
out at individual dates using the GLM procedure in SAS (SAS Institute, Cary, NC.)
Differences were declared significant at p=0.05 using Fisher’s protected least significant

difference test (LSD). Original data was assumed normally distributed and passed a

Levene’s test for equal variance at p=0.01. Mean separation of bud primordia LT5os in

the potted raspberry experiment was conducted with two outliers removed that fell

71

 

outside of 1.5 times the interquartile range (Sokal and F ohlf, 1981). Pearson correlation

coefficients between LT50 and carbohydrate percent dry weight were determined using .

the CORR procedure in SAS.

Results

High tunnel and field cultivar comparisons

Ambient air temperatures at SWMREC during the fall and winter of 2007-08 and 2008-
09 are shown in Figure 3-1. Temperatures less than 0 °C occurred prior to the first cold
hardiness sampling dates of 8 Nov. 2007 and 30 Oct. 2008. Freezing temperatures
occurred on 28 Oct., 1, 2, and 7 Nov. 2007 as well as 22, 27, 29, and 30 Oct. 2008. High
tunnel plastic was removed on 14 Nov. 2007 and 11 Nov. 2008, after which high tunnel

raspberry plants were exposed to ambient temperatures.

Maximum and minimum temperatures flom within the high tunnel in 2008 were
compared to a weather station less than 200 m away (Figure 3-2). No tunnel
temperatures were recorded in 2007. Maximum daily temperatures in the high tunnel
averaged 7 °C higher than in the field during the last three weeks of August and 6 °C
higher during all of September. Minimum temperatures were 0.3 and 0.2 °C higher for
the same time periods, respectively. In 2008, sides and end walls were put on the tunnel
on 17 Oct. Scaling the high tunnel dramatically changed the differences between high
trmnel and weather station temperatures. Between 17 and 29 Oct. 2008, maximum daily

temperatures were 14 °C higher in the enclosed tunnel while the minimum daily

temperatures were only 0.4 °C higher in the trmnel.

72

 

Growing degree days calculated flom temperatures with in the high tunnel and at
a weather station are shown in Figure 3-3. Accumulated GDD for the high tunnel and
weather station were 1546 and 1022, respectively. When the tunnel was sealed flom 17
to 29 Oct. 2008, the tunnel and weather station accumulated 150 and 18 GDD,

respectively.

Cold hardiness. Cultivars did not differ in bud primordia hardiness during the winter of
2007-08 (Table 3-1). During cold acclimation in 2008, cultivar differences in bud

primordia hardiness were observed in late October and early November (Table 3-2).

When differences were detected, ‘Nova’ had lower LT50 values (more cold hardy) than

the other cultivars. In October, the same differences between cultivars existed in both the

high tunnel and field environment. Bud primorida LT50 values observed in high tunnel-

grown plants typically resembled those grown in the field. Mean LT5os of bud primorda

across cultivars on 30 Oct., 13 and 29 Nov. and 6 and 26 (field) or 29 (tunnel) Dec. 2008
were -14.2, -20.3, -25.3, -25.3, and -25.2 for tunnel plants and -15.1, -19.7, -25.2, -25.6,

and -25.2 for field plants, respectively.

Significant differences in cambium cold hardiness between cultivars were
observed in Jan. and Mar. 2008 (Table 3-1) and during cold acclimation later that year
(Table 3-2). ‘Nova’ was significantly hardier than ‘Canby’ at all dates where statistical
significance was declared. A general trend was that ‘Nova’ was more hardy than

‘Canby’ and ‘Encore’ in both bud primordia and cambium tissues at most sampling dates.

73

Bud primordia were consistently less hardy than cambium tissue. Mean LT508

for tissue types across cultivar and growing environment (tunnel and field) on 30 Oct., 13
and 29 Nov. and 6 and 26 (field) or 29 (tunnel) Dec. 2008 were -14.7, -20.0, -25.3, -25.6,
and -25.2 for bud primordia and -15.9, -28.1, -29.7, -31.2, and -30.2 for cambium,
respectively. Bud primordia and cambium tissues were most similar on 30 Oct. 2008 and
were less alike at later dates. Bud primordia reached maximum cold hardiness on 29

Nov. 2008 whereas cambium tissues reached maximum cold hardiness earlier on 13 Nov.

2008. The average LT50 values for bud primorida of high tunnel and field grown plants

decreased by approximately 5 °C (increased cold hardiness) between 13 and 29 Nov.

2008 when cambium tissue average LT50 values decreased by less than 1 °C.

Tissues of ‘Heritage’ sampled approximately every month throughout the 2007-
08 winter showed similar differences between bud primordia and cambium cold
hardiness (Figure 3-4). By late December, bud primordia and cambium tissue reached
maximum cold hardiness on approximately the same date in late December. While there
were no differences in bud primordia cold hardiness on any date for ‘Heritage’ red
raspberry, it appears that high tunnel cambium tissue was hardier than field cambium

tissue in J an., Feb. and Mar. 2008.

Carbohydrates. Soluble carbohydrates in raspberry cane tissue during late fall and
winter include fluctose, glucose, sucrose, and raffinose. Low levels of inositol were
found in a few samples (data not shown). Fructose and glucose concentrations were very
similar at all sampling dates in both 2007-08 and 2008 (Figures 3-5 and 3-6). Generally,
glucose levels were higher in ‘Canby’ than other cultivars, with statistical significance

74

being declared in high tunnel grown samples on 18 Jan. and 14 Mar. 2008 (Table 3-3).
Glucose levels in ‘Canby’ were also higher during the winter season of 2008 when

significance could be declared (Table 3-4).

Cultivars did not differ in fluctose levels on any date (data not shown). Mean
fluctose levels across all cultivars on 8 Nov. 2007, 18 J an., and 14 Mar. 2008 were 0.8%,
1.9%, and 1.6% of dry weight for tunnel plants and 0.7%, 1.9%, and 1.9% for field
plants, respectively. Mean fluctose levels across all cultivars on 14 Aug, 30 Oct., 13 and
29 Nov. and 6 and 26 (field) or 29 (tunnel) Dec. 2008 were 1.3%. 0.7%, 1.1%, 1.5%,
1.8%, and 2.0% of dry weight for tunnel plants and 1.1%, 1.1%, 1.1%, 1.6%, 1.8%, and

2.2% for field plants, respectively.

Sucrose was the most abundant soluble carbohydrate on all sampling dates.
Sucrose, fluctose, and glucose concentrations were very low on 14 Aug. 2008 (Table 3-
4). Sucrose levels did not vary significantly between cultivars in the tunnel and field on
any date during the fall and winter of 2007-08. Mean sucrose levels across cultivars on 8
Nov. 2007, 18 Jan. and 14 Mar. 2008 were 3.8%, 5.8%, and 5.9% of dry weight in tunnel

plants and 2.9%, 5.4%, and 5.6% in field plants, respectively.

Raffinose was present at lower levels than all other soluble carbohydrates at all
sampling dates (Figures 3-5 and 3-6). No raffinose was present on 14 Aug. 2008 in any
cultivar but was present in small amounts at every other sampling date in all cultivars.
Raffinose levels were significantly higher in ‘Nova’ flom the field on all sample dates in
2007-08 and 2008 compared to other cultivars (Tables 3-3 and 3-4). When significant,

raffrnose levels of ‘Nova’ grown under high tunnels were higher than the other cultivars.

75

Starch levels were highest on the first sampling date each season (Figures 3-5 and
3-6). High tunnel starch levels were appeared greater than field levels on all sampling
dates in the fall and winter of 2008, although statistical comparisons cannot be made.
Cultivars did not vary significantly in starch concentration in the tunnel or field during
the fall and winter of 2007-08. Mean starch levels across cultivars on 8 Nov. 2007, 18
Jan. and 14 Mar. 2008 were 2.2%, 0.8%, and 0.7% of dry weight in tunnel plants and

2.1%, 0.3%, and 0.5% in field plants, respectively.

Total soluble carbohydrates (fluctose + glucose + sucrose + raffinose) did not
vary between cultivars or between tunnel and field plants in the fall and winter of 2007-
08 or 2008. Total soluble carbohydrate levels were highest in tunnel and field grown
plants on 18 Jan. 2008 and 26 or 29 Dec. 2008. Mean total soluble carbohydrate levels
across all cultivars on 8 Nov. 2007, 18 Jan. and 14 Mar. 2008 were 6.2%, 10.2%, and
9.5% of dry weight in tunnel plants and 4.7%, 9.3%, and 9.3% in field plants,
respectively. Mean total soluble carbohydrate levels across all cultivars on 14 Aug, 30
Oct., 13 and 29 Nov., and 6 and 26 (field) or 29 (tunnel) Dec. 2008 were 3.2%, 5.0%,
6.5%, 9.1%, 10.0%, and 10.8% of dry weight in tunnel plants and 2.9%, 6.1%, 5.9%,

9.5%, 9.6%, and 11.6% in field plants, respectively.

Total nonstructural carbohydrates (starch + total soluble carbohydrates) showed
no consistent differences between cultivars on any sampling date. Levels of total
nonstructural carbohydrates were lower on 8 Nov. 2007 in high tunnel and field plants
compared to the other two sampling dates that winter. In the 2008 season, total
nonstructural carbohydrate levels were relatively constant across dates; however, on 14

Aug. 2008 levels were less than half of 30 Oct. 2008 levels. Mean total nonstructural

76

carbohydrate levels across all cultivars on 8 Nov. 2007, 18 Jan. and 14 Mar. 2008 were
8.4%, 11.1%, and10.2% of dry weight in tunnel plants and 6.8%, 9.6%, 9.8% in field
plants, respectively. Mean total nonstructural carbohydrate levels across all cultivars on
14 Aug, 30 Oct., 13 and 29 Nov., and 6 and 26 (field) or 29 (tunnel) Dec. 2008 were
3.5%, 11.4%, 11.4%, 11.0%, 10.9%, and11.3% of dry weight in tunnel plants and 3.7%,

9.5%, 8.7%, 10.7%, 10.3%, and 11.9% in field plants, respectively.

Carbohydrate levels at monthly intervals are shown in Figure 3-7 for ‘Heritage’
grown in the fall and winter of 2007-08. Soluble carbohydrate levels were lowet on 8

Nov. 2007 and highest on 27 Dec. 2007. High tunnel and field grown plants behaved
similarly except that starch levels continued to increase through early November for high

tunnel grown plants, whereas that same increase was not observed in the field.

LT50 and carbohydrate correlations. The relationship between LT50 values and

carbohydrate concentrations in plants flom the two environments (tunnel and field) were
evaluated across all cultivars at all dates, across cultivars for individual dates, and across
cultivars for individual dates in the tunnel and field separately (Tables 3-5, 3-6, and 3-7).
When data from all cultivars, dates, and environments (tunnel and field) were pooled,

strong correlations were observed both in the fall and winter of 2007-08 as well as 2008.

Pearson correlation coefficients between LT50 and fluctose, glucose, sucrose, starch, and

total soluble carbohydrates across all cultivars, dates, and environments were significant

at PS0.005 in the winter season of 2007-08, 2008, and for ‘Heritage’ sampled monthly.

Raffinose was not as strongly correlated with LT50 during the winter season of 2007-08

or in ‘Heritage’ sampled monthly. All individual soluble carbohydrates as well as total

77

 

soluble carbohydrates were negatively correlated with LT50 values while starch was

positively correlated with LT50 values.

Potted raspberry experiment

Cold hardiness. Ambient air temperatures at SWMREC during the fall and winter of
2008 during the time potted raspberry plants were being moved flom under the high
tunnel to the outside environment are shown in Figure 3-8. Ambient temperatures were
relatively warm at the time of cold hardiness sampling (6 Nov. 2008), as daily maximum
temperatures in the three days prior to sampling were above 20 °C. Freezing

temperatures occurred prior to cold hardiness sampling on 22, 27, 29 and 30 Oct. 2008.

Cambium LT50 values were not significantly affected by the removal date from

the high tunnel, cultivar, or removal date and cultivar interaction. Mean cambium LT50

values (1: SE) across cultivars removed flom the high tunnel on 14 Aug, 11 Sep., 9 Oct,

and 6 Nov. 2008 (control) were -19.7 $0.3, -20.6 :tO.3, -18.8 10.3, and -18.5 i0.2 °C,
respectively.

When analyzing bud primordia cold hardiness, two observations were removed
flom the. data set as outliers because the LT50 values calculated were greater than 1.5
times the interquartile range (Sokal and Rohlf, 1981). Interestingly, all removal date x
cultivar means for bud primordia LT50 were lower than cambium means, indicating bud

primordia were more cold hardy. Statistical analysis performed after outliers were

removed showed no removal date x cultivar effect or cultivar effect, but a significant

78

 

removal date effect on cold hardiness. Control plants that remained under the high tunnel

through November had bud primordia that were significantly more cold hardy than those

removed in August or September. Bud primordia LT50 least square means across

cultivars removed from the high tunnel on 14 Aug, 11 Sep., 9 Oct, and 6 Nov. 2008

(control) were -22.7, -23.2, -21.7, and -20.3, respectively.

Carbohydrates. Analysis of variance indicated that the main effect of cultivar was
significant for all carbohydrates measured, and cultivar means across all removal dates
are listed in Table 3-8. The main effect of removal date was not significant for any
carbohydrate, and the interaction of cultivar and removal date was not significant for any
carbohydrate measurement, with the exception of total soluble carbohydrates (P=0.0415).
In non-significant situations, the interaction effect was dropped flom the model and main
effects were analyzed. Because the interaction effect observed for total soluble
carbohydrates was not strongly significant, cultivar means were included in Table 3-8.
Across all high tunnel removal dates, ‘Canby’ had significantly higher levels of fluctose
and glucose than the other two cultivars, but lower levels of sucrose, raffinose, and total
soluble carbohydrates. Starch and total nonstructural carbohydrates were not

significantly different between cultivars. No consistent correlations could be made
between LT50 values and carbohydrate levels of plants sampled on 6 Nov. 2008 (Table 3-

9).
Discussion

These studies suggest that growth under 3-season high tunnels, having plastic

sides and ends put on in mid-October and plastic removed in early November, do not '

79

dramatically influence the acclimation process or mid-winter hardiness of raspbenies.
Cold hardiness of tunnel and field tissues was often similar on the same date, although
the experimental design did not allow for statistical comparison of the two environments.
It was expected that high tunnel plants might be more susceptible to cold injury on the
first cold hardiness sampling date each year (8 Nov. 2007 and 30 Oct. 2008) since plastic

had not yet been removed flom the high tunnel. The data appear to show little difference

in LT50 between tunnel and field tissues at those dates (Tables 3-1 and 3-2), suggesting

" M'a‘dflfl.‘ “1‘“. o."— ——F

that high tunnel and field plants were equally acclimated under high tunnels at that point

 

in time.

Simulating tunnel plastic removal times by moving potted raspberry plants out of
a tunnel at different dates had inconsistent effects on cold hardiness in early November.
Plants removed flom tunnel conditions earlier in the fall were expected to acclimate to
cold earlier than plants remaining in the tunnel until November because growth cessation
would likely occur earlier as a result of lower maximum temperatures outside the trmnel.
Early removal flom the tunnel environment did not affect cambium cold hardiness,
although bud primorda of plants moved in August and September were significantly
hardier than those remaining under plastic through the beginning of November.
Removing tunnel plastic in August or September increased bud primordia cold hardiness
by 2.4 to 2.9 °C, respectively compared to plants remaining under cover. Sampling cold
hardiness at additional dates during cold acclimation would help better describe the effect
early plastic removal has on raspberry cold hardiness. If no consistent differences are
observed, high tunnel plastic over FF raspberry cultivars could be removed when it is

convenient and labor is available instead of waiting until November.

80

The similarity between high tunnel and field hardiness may be explained by the
interaction of maximum and minimum temperatures. Tunnels elevate maximum daily
temperatures substantially, but minimum daily temperatures are similar to those in the
field (Figure 3-2). This difference in maximum and minimum temperatures under
tunnels was particularly evident when tunnel sides and ends were enclosed flom 17 to 29
Oct. 2008. Our temperature data trends are similar to those of other high tunnel
researchers (Kadir et al., 2006; Rader and Karlsson, 2006). Perhaps the low night
temperatures under tunnels allow plants to cold acclimate as normal but elevated daytime
temperatures allow for continued photosynthesis and growth. Little information
addressing the effect of day/night temperature differences (DIF) on cold acclimation is
available. Internode length and plant height of herbaceous plants is known to be affected
by DIF (Myster and Moe, 1995). Perennial plants of Camus stolanifera exposed to 20/15
°C (day/night) temperatures for 28 days followed by 15/ 5 °C temperatures were taller and
more cold resistant than plants grown continuously at the cooler regime (Fuchigami et al.,
1971). This information does not directly apply to a tunnel situation because treatments

were not differences between day/n1 ght temperatures.

Kalcsits et al. (2009) found that hybrid poplar species grown at 18.5/3.5 °C (day/
night) ceased growth later and were also less cold hardy than plants grown at 135/85,
185/ 13.5, and 23.5/8.5 °C. The authors suggest that the warm night temperature
treatment (1 8.5/ 13.5 °C) accelerates growth cessation, dormancy, and cold acclimation in
the four genotypes that were trialed (Kalcsits et al., 2009). Two treatments in the study
had a 5 °C DIF while two had 15 °C. Again, this study was not testing the effect of

differences between day/night temperatures and characterizing the effects of positive DIF

81

 

on cold acclimation in woody plants would be helpful, particularly because high positive

DIF is unavoidable in high tunnel situations.

The current study showed that bud primordia and cambium tissues of ‘Nova’ were

more hardy than those of ‘Canby’ or ‘Encore’ during early cold acclimation in 2008
(Table 3-2). Mean LT50 for ‘Nova’ was often the lowest of the three cultivars, but
statistical significance could not always be declared. Based on bud primordia, ‘Canby’
was less hardy than ‘Nova’ at early sampling dates but similar in hardiness at later dates

(Table 3-2), suggesting that ‘Canby’ may acclimate more slowly than ‘Nova’ but

eventually reach similar mid-winter hardiness levels.

Cane dieback of these cultivars following a severe winter has previously been

discussed (Hanson et al., 2005); ‘Nova’ was less injured than ‘Canby’ and ‘Encore’.

‘Canby’ has been described as a hardy cultivar with a mid-winter LT50 of -30 °C

(Hummer, 1995), but ‘Encore’ and ‘Nova’ were not tested for comparison. While ‘Nova’
was bred flom the cold hardy raspberries ‘Southland’ x ‘Boyne’ (Jarnieson, 1989), this
appears to be the first instance of the cultivar’s hardiness being characterized during cold

acclimation.

In addition to hardiness during cold acclimation, mid-winter hardiness of canes

grown in tunnel and field environments also was of interest. Comparison of high tunnel

and field LT50 values showed no obvious indications that one was more cold hardy than

the other during mid-winter. When cultivars differed significantly flom one another,

‘Nova’ was the hardiest cultivar. Patterns of acclimation to cold were similar to those

82

 

described by Palonen (1999). Maximum cold hardiness was reached by late November in
both the high trmnel and field environments in 2007, and this level of hardiness was
retained through March in 2008 (Table 3-1). From January to March in 2008, the
cambium of ‘Heritage’ raspberry appeared to be hardier than field grown tissues but
statistical replication is lacking to confirm this difference. Replicated cold hardiness
sampling as plants are deacclirnating would be helpful to determine if tunnel and field
cultivars differ in their ability to retain hardiness in the spring until threat of frost damage

is gone.

Soluble carbohydrates have been shown to increase during cold acclimation in
raspberry (Bennett and Weeks, 1960; Jennings and Carmichael, 1975; Palonen, 1999) and
other woody plants (Levitt, 1980) while starch decreases (Jennings and Carmichael,
1975). The present study confirms the presence and increase during cold acclimation of
fructose, glucose, sucrose, and small amounts of raffinose in red raspberry canes (Burly,
1961; Palonen, 1999, Palonen et al.,2000). These associations have been observed

previously in Rubus (Kaurin et al., 1981; Palonen, 1999).

The levels of total nonstructural carbohydrates in canes during the fall and winter
of 2008 remained relatively consistent under the tunnel (Figure 3-5). The canes of
cultivars grown in the field reached levels of nonstructural carbohydrates seen under
tunnels by late December. Total soluble carbohydrate levels were similar in tunnel and
field canes in 2007-08 and 2008. This work demonstrated strong positive correlations

between individual as well as total soluble carbohydrates and cold hardiness (negative

correlation with LT50) as noted in Tables 3-5, 3-6, and 3-7.

83

Sucrose was the most abundant soluble carbohydrate throughout cold acclimation
and has been shown to enhance cold hardening when added to the culture medium of
rrricropropagated raspberry (Palonen and J unttila, 1999). Interestingly, very little sucrose
was present on 14 Aug. 2008 and glucose and fluctose were present in higher quantities
(Table 3-4). This could indicate that glucose and fluctose may be present in greater
quantities when plants need readily available sources of energy and are actively growing.
The levels of glucose and fluctose across all removal dates in the potted experiment were
significantly higher in the canes of ‘Canby’ than those of other cultivars (Table 3-8).
Carbohydrates in the potted experiment were analyzed on 6 Nov. 2008 before plants were

fully acclimated. Higher levels of glucose and fluctose in ‘Canby’ may indicate the

cultivar was less acclimated than the others. The mean LT50 for ‘Canby’ bud primordia

across all removal dates was higher than for the other cultivars, although not statistically

significant (data not shown).

Raffinose was observed in lower concentrations than other soluble carbohydrates
in this study but was often highest in the hardiest cultivar ‘Nova’ (Tables 3-3 and 3-4).
Raffinose has been observed to accumulate in cold acclimating woody (Keller and
Loescher, 1989) and herbaceous plants (Bachman et al.,1994, Pennycooke et al., 2003),
and is believed to be an important storage carbohydrate and cryoprotectant (Irnanishi et

al., 1998).

The concentration of starch in raspberry cane tissue was lowest when plants had
the greatest cold hardiness, although starch was also low on 14 Aug. 2008. This may be

explained by the fact that raspberry primocanes are in an active growth phase during late

84

 

August and would not be storing photosynthate as starch at this time. Engard (1 93 9)
noted that starch was never abundant in canes during the growing season. A strong

negative correlation was observed between starch and cold hardiness (positive correlation

with LT50) as shown in Tables 3-5, 3-6, and 3-7. The highest levels of starch observed in

tunnel and field raspberry canes were observed when plastic remained on the high tunnels
on 8 Nov. 2007 and 30 Oct. 2008 (Figures 3-5 and 3-6) with high tunnel canes having
relatively greater starch concentrations. Figure 3-7 shows how levels of starch in high

tunnel canes of ‘Heritage’ increase in early November while field cane starch levels

 

"Ir- ' “331...... ,

decreased. This may result flom a greater ability of canes under high tunnels to
photosynthesize during late fall and retain photosynthate since low night temperatures

limit respiration.

Conclusions

This study investigated the cold hardiness of red raspberry cambium and bud primordia
under high tunnel and field conditions during cold acclimation. Bud primordia and
cambium tissues of ‘Nova’ were typically hardier throughout cold acclimation and at
maximum mid-winter hardiness than ‘Canby’ and ‘Encore’. Bud primordia across all
cultivars appeared to be less hardy than cambium tissues, particularly in December.
Removing high tunnel plastic after FF cultivars finished fluiting (August, September)
increased bud primordia hardiness slightly but had no effect on cambium hardiness.
Minimum night temperatures appear to have more of an effect on cold acclimation than
maximum day temperatures, since cold hardiness under tunnel and field environments

were similar. Replicated experiments to simulate high tunnel and field conditions with

85

the use of growth chambers at various day/night temperature regimes could test this
assumption. Soluble carbohydrates were positively correlated with cold hardiness while
starch was negatively correlated. Raffinose concentrations were significantly higher in
‘Nova’ than ‘Canby’ though not statistically higher than ‘Encore’, on all sampling dates
in field canes and on several dates in tunnel canes. These studies suggest that replicated
experiments testing tunnel and field conditions could elucidate any potential statistical
differences between the two enviromnents. Hardiness during deacclimation was not
investigated in these studies and the susceptibility of raspberry tissues grown in ttmnel
and field environments to fleeze/thaw cycles in early spring should be characterized in

the future.

86

 

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91

 

' 2007-2008

    

 

0 0,02,.... ‘ ‘

 

 

Q 2
Maximu 111 Temperature E
'20 ‘ High tumIVlinimunTemperature 1ture at SWMRE F " onnn
plastic removed + Maximum
'-~0-~- Minimum

 

 

2008-2009

Temperature (°C)

 

 

 

 

- High tunnel
plastic removed
-30 1 t 'T l 1
Oct Nov Dec Jan Feb Mar
Date

Figure 3-1. Maximum and minimum ambient air temperatures at the Southwest Michigan
Research and Extension Center (SWMREC) in Benton Harbor, MI flom 15 Oct. to 20 Mar.
in 2007-2008 (top) and 2008-2009 (bottom). Solid arrows indicate dates where multiple
cultivars were sampled. Arrows with dots indicate dates where only ‘Heritage’ was sampled.
Bold arrows indicate high tunnel plastic removal (14 Nov. 2007 and 11 Nov. 2008).

92

 

 

 

 

 

Temperature (°C)

 

$.06
ii?
“is.

10

fits?

0 —O-— Tunnel Maximum A:i
' ........ 0 ....... ' ' ---------------

Weather Station Maxrrnum

 

 

 

 

 

- - 'V- - - Tunnel Minimum
— - - -A- — -° Weather Station Minimum
-10 r 1
Aug Sep Oct

Date

Figure 3-2. Maximum and minimum temperatures for high tunnel and ambient
conditions in 2008. High tunnel temperatures flom 8 Aug. to 8 Oct. are an average of 3
data loggers at 1.5 m height in the raspberry canopy. High tunnel temperatures flom 10
Oct. to 29 Oct. are an average of 3 data loggers at 1.4 m height above the raspberry
canopy. Ambient conditions are recorded flom an automated weather station less than
200 m flom the high tunnel. The arrow indicates the date tunnels were enclosed with
sides and ends (17 Oct).

93

 

1800

 

1600 q — High Tunnel
------- Weather Station

 

 

 

1400 -

1200 -

1000 -

GDD

800 -

600 -

400 -

 

 

 

 

 

Aug Sep Oct
Date

Figure 3-3. Accumulated growing degree days (GDD), with a base temperature of 10 °C,
for 3-season high tunnel and ambient conditions in 2008. High tunnel GDD flom 8 Aug.
to 8 Oct. are an average from 3 data loggers at 1.5 m height in the raspberry canopy.
High tunnel GDD flom 10 Oct. to 29 Oct. are an average flom 3 data loggers at 1.4 m
height above the raspberry canopy. Ambient conditions are recorded flom an automated
weather station less than 200 m flom the high tunnel. The arrow indicates the date
trmnels were enclosed with sides and ends (17 Oct.).

94

Table 3-1. Mean LTSOZ values and number (n) of

observations if less than 3 for bud primordia and cambium
tissues of red raspberry cultivars grown under high tunnel
and field conditions in 2007-08.

 

 

 

Bud primordig Cambium
Cultivar Tunnely Field Tunnel Field
m
‘Canby’ -12.5 a -13.2 a
‘Encore’ -11.7 a(2)
‘Nova’ -13.6 a(2) -15.5 a(2)
18 Jan.
‘Canby’ -25.2 a -24.6 a -31.0 a -3l.0 a
‘Encore’ -19.6 a(2) -33.3 a -28.6 a
‘Nova’ -23.1 a -27.1 a -36.9 b -34.3 a
M
‘Canby’ -24.9 a -24.5 a -34.5 a -30.5 a
‘Encore’ -22.8 a -21.3 a -32.8 a -27.9 a
‘Nova’ -21.9 a -20.6 a(2) -37.5 b -31.7 a(2)

 

zLT;,0 is the temperature at which 50% of sampled tissue is
estimated to be killed.

yMeans within columns on the same date followed by differing
letters are significantly different at P=0.05 by LSD.

95

 

Table 3-2. Mean LT50z values for bud primordia and

cambium tissues of red raspberry cultivars grown under high
tunnel and field conditions in 2008.

 

 

 

Bud mmordia Cambium
Cultivar Tunner Field Tunnel Field
30 Oct.
‘Canby’ -12.5 a -12.6 a -15.1 a -12.8 a
‘Encore’ -13.9 ab -l4.9 ab -15.0 a -17.1 b
‘Nova’ -16.1 b -17.7 b -17.0 a -l8.4 b
13 Nov.
‘Canby’ -19.0 a -19.8 b -31.0 a -26.8 a
‘Encore’ -20.4 a -l8.1 a -31.2 a -25.9 a
‘Nova’ -21.6 a -2l.2 c -28.8 a -24.7 A
29 Nov.
‘Canby’ -25.7 a -25.5 a -27 .4 a -25.9 a
‘Encore’ -25.0 a -24.3 a -28.8 a -28.7 a
‘Nova’ -25.3 a -25.9 a -31.7 a -35.7 a
6 Dec. -
‘Canby’ -26.3 a -26.4 a -29.2 a -27.4 a
‘Encore’ -24.5 a -24.6 a -31.5 a -30.8 a
‘Nova’ -25.2 a -26.4 a -35.1 a -33.0 a
29 Dec. 26 Dec. 29 Dec. 26 Dec.
‘Canby’ -25.6 a -26.6 a -28.7 a -25.0 a
‘Encore’ -24.7 a -23.7 a -29.8 a -29.0 b
‘Nova’ -25.4 a -25.0 a -33.1 a -35.4 c

 

zLT5Q is the temperature at which 50% of sampled tissue is

estimated to be killed.

yMeans within columns on the same date followed by differing
letters are significantly different at P=0.05 by LSD.

96

 

 

 

LT50

 

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/

-15 -

-20 ..

-25 -

-30 _

-35 .4

-40 -

—0- High Tunnel
—0— Field

 

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W

 

 

-10;
-15 -
-20 -
-25 .
-30 -
-35 -

-40 4

 

Cambium

 

 

Dec Jan

Date

97

Figure 3-4. Mean LT50 values of bud primordia (top) and cambium (bottom) of 'Heritage'
red raspberry grown under high tunnel and field conditions in 2007-08. Vertical bars
indicate standard errors for individual means. Means containing two replications were:
field bud primordia on 27 Dec. and tunnel cambium on 8 Nov., 28 Nov., and 27 Dec. All
other means contained three replications.

WI. mi”. 2*

 

+ Fructose

 

—0— Glucose + Raffmose + Total soluble carbohydrates
+ Sucrose -—Ct— Starch + Total nonstructural carbohydrates
‘4 'Canby' (field) 'Canby'( e1)
12 - --
IO 2 +

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2.'1..><:KSfi—o
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W

 

 

 

 

 

 

 

 

53th
at

 

 

 

 

 

 

 

 

fi’ I F

Nov Dec Jan Feb Mar Nov Dec Jan Feb Mar
Date
2007-2008

Figure 3-5. Changes in percent dry weight of soluble carbohydrates (fluctose, glucose,
sucrose, and raffinose), total soluble carbohydrates (sum of previous), starch, and total
nonstructural carbohydrates (starch + soluble carbohydrates) in the canes of red raspberry
cultivars grown under high tunnel and field conditions in 2007-08. Vertical bars indicate
standard errors for individual means.

98

 

+ Fructose

 

 

 

—0- Glucose —A— Raffmose + Total soluble carbohydrates
14 + Sucrose —CI— Starch + Total nonstructural carbohydrates
'Canby' (field) 'Canby' ( e1)

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'Nova' (field) 'Nova' (tunnel
1 2 d -
1 O -4 ..
8 .1 .
5 , .
4 .
2 4
Date
2008

. Figure 3-6. Changes in percent dry weight of soluble carbohydrates (fluctose, glucose,
sucrose, and raffinose), total soluble carbohydrates (sum of previous), starch, and total
nonstructural carbohydrates (starch + soluble carbohydrates) in the canes of red raspberry
cultivars grown under high tunnel and field conditions in 2008. Vertical bars indicate
standard errors for individual means.

99

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Nov Dec Jan Feb Mar

Date

 

Figure 3-7. Changes in percent dry weight of soluble carbohydrates (fi'uctose, glucose,
sucrose, and raffinose), total soluble carbohydrates (sum of previous), starch, and total
nonstructural carbohydrates (starch + soluble carbohydrates) in the canes of ‘Heritage’
red raspberry grown under high tunnel and field conditions in 2007-08. Vertical bars

indicate standard errors for individual means.

102

 

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+ Maximum
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Aug Sep Oct Nov
Date

Figure 3-8. Maximum and minimum ambient air temperatures at the Southwest Michigan
Research and Extension Center (SWMREC) in Benton Harbor, MI from 1 Aug. to 10

Nov. in 2008. Solid arrows indicate dates potted plants were moved outside of the high
tunnel. Dotted arrow indicates the date of cold hardiness sampling.

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