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Haskap Preharvest Fruit Drop and Stop-drop Treatment Testing

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Haskap ( Lonicera caerulea ), also known as honeyberry, is a relatively new fruit crop in North America. To date, most academic activity and research in North America involving haskap has focused on cultivar development and health benefits, with relatively few field experiments providing information to guide field planning and harvest management for the recently released cultivars. In 2020, we documented preharvest fruit drop (PHFD) rates for 15 haskap cultivars planted in a randomized block design at our research center in western Montana with the aim of preliminarily determining whether certain cultivars may be prone to this phenomenon. Additionally, we evaluated two plant growth regulators (PGRs) to reduce PHFD in two cultivars previously observed to have high rates of PHFD. Results suggest cultivar-specific variations in PHFD near berry maturation. Because haskap harvest indices are not well-defined and may be cultivar-specific, we share our 1-year study results as preliminary information and as a call for further research. Cultivars Aurora, Boreal Blizzard, Borealis, Indigo Gem, Kapu, and Tana all had PHFD rates less than 12% of yield, where yield is the weight of berries lost to PHFD plus marketable yield and marketable yield is fruit remaining on the shrub at harvest. Cultivars Chito, Kawai, and Taka had the highest rates of PHFD, although marketable yields were still relatively high, especially for Kawai. We note that ease of fruit detachment is an important consideration in mechanical harvest, and this characteristic could be advantageous if managed appropriately. The PGRs evaluated (1-napthaleneacetic acid and aminoethoxyvinylglycine) did not influence PHFD rates; however, our study was limited by the sample size and by the lack of information regarding haskap abscission physiology. In summary, the haskap cultivars evaluated exhibited variable PHFD rates in the year of the study, and further research is needed to understand haskap fruit maturation, harvest indices, and abscission.
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Haskap Preharvest Fruit Drop and Stop-drop
Treatment Testing
Rachel Leisso
1
, Bridgid Jarrett
1
, and Zachariah Miller
1
ADDITIONAL INDEX WORDS. blue honeysuckle, camerise, honeyberry,
Lonicera caerulea, plant growth regulators
SUMMARY.Haskap(Lonicera caerulea), also known as honeyberry, is a relatively new
fruit crop in North America. To date, most academic activity and research in North
America involving haskap has focused on cultivar development and health benets,
with relatively few eld experiments providing information to guide eld planning and
harvest management for the recently released cultivars. In 2020, we documented
preharvest fruit drop (PHFD) rates for 15 haskap cultivars planted in a randomized
block design at our research center in western Montana with the aim of preliminarily
determining whether certain cultivars may be prone to this phenomenon. Additionally,
we evaluated two plant growth regulators (PGRs) to reduce PHFD in two cultivars
previously observed to have high rates of PHFD. Results suggest cultivar-specic
variations in PHFD near berry maturation. Because haskap harvest indices are not
well-dened and may be cultivar-specic, we share our 1-year study results as
preliminary information and as a call for further research. Cultivars Aurora, Boreal
Blizzard, Borealis, Indigo Gem, Kapu, and Tana all had PHFD rates less than 12% of
yield, where yield is the weight of berries lost to PHFD plus marketable yield and
marketable yield is fruit remaining on the shrub at harvest. Cultivars Chito, Kawai,
and Taka had the highest rates of PHFD, although marketable yields were still
relatively high, especially for Kawai. We note that ease of fruit detachment is an
important consideration in mechanical harvest, and this characteristic could be
advantageous if managed appropriately. The PGRs evaluated (1-napthaleneacetic acid
and aminoethoxyvinylglycine) did not inuence PHFD rates; however, our study was
limited by the sample size and by the lack of information regarding haskap abscission
physiology. In summary, the haskap cultivars evaluated exhibited variable PHFD rates
in the year of the study, and further research is needed to understand haskap fruit
maturation, harvest indices, and abscission.
Haskap (Lonicera caerulea),
also known as honeyberry or
blue honeysuckle, is a relatively
new berry crop in North America. The
woody perennial shrub produces edible
blue berries that vary greatly in avor,
shape, and size. The avor has been
described as a combination of raspberry
(Rubus sp.) and blueberry (Vaccinium
sp.) (Bors et al., 2012), ranging from
mild, sweet, variably tart, to slightly bit-
ter (Thompson, 2006). Studies have
indicated the berries have higher antioxi-
dant capacity than many other small fruit
crops, including blueberry (Rupasinghe
et al., 2012), and a review of the recent
literature lists numerous health benets,
including anti-diabetic, anti-inamma-
tory, and anti-cancer properties (Rupa-
singhe et al., 2018).
In Montana, average fruit weights
of North American commercial culti-
vars are between 0.96 and 1.70 g (Set-
zer, 2020), and the shape varies from
rounded oval to greatly elongated
(Bors et al., 2015). Haskap can be
grown in areas that are too cold or
alkaline for blueberry because of its tol-
erance to a wide range of soil pH (up
to 8.0) and exceptional cold hardiness
(Bors et al., 2012, 2015; Gerbrandt,
2014). In addition, their blossoms can
withstand freezing temperatures (Gasic
et al., 2018). It is an early-season fruit
crop and, in some locations, it ripens
before or concurrent with June-bear-
ing strawberry [Fragaria ×ananassa
(Gerbrandt, 2014; Gerbrandt et al.,
2017)]. Pollinizer plants (compatible
cultivars) are required for good fruit set
(Gerbrandt, 2014; Plekhanova, 1996).
Haskap breeding materials, collec-
tion, evaluation, and breeding efforts
(Bors et al., 2009, 2012, 2015;
Gerbrandt et al., 2017, 2018, 2020;
Thompson, 2006, 2016a, 2016b,
2016c, 2016d, 2017a, 2017b; Thom-
pson and Barney, 2007) have sup-
ported the expanding industry in both
the United States and Canada. Cana-
dian haskap production increased 64%
from 2018 to 2019 (Statistics Canada,
2020), and farms range in size from 0.5
to 40 acres or more. Haskap produc-
tion in the United States is not tracked
by government reporting.
Although the amount of informa-
tion about haskap cultivars and their
cultivation is increasing (Jurikova et al.,
2009; Małodobry et al., 2010; Skupie
n
et al., 2009), details regarding cultivars
typically available in North America are
Units
To convert U.S. to SI,
multiply by U.S. unit SI unit
To convert SI to U.S.,
multiply by
0.0781 oz/100 gal mLL
1
12.8000
0.0731 oz/acre Lha
1
13.6840
0.3048 ft m 3.2808
3.7854 gal L 0.2642
10 gal/100 gal Lm
3
0.1
2.54 inch(es) cm 0.3937
25.4 inch(es) mm 0.0394
1.1209 lb/acre kgha
1
0.8922
28.3495 oz g 0.0353
1 ppm mgL
1
1
1 ppm mLL
1
1
(F32) 1.8 FC(
C × 1.8) 132
Received for publication 6 June 2021. Accepted for
publication 25 Aug. 2021.
Published online 18 October 2021.
1
Department of Research Centers, Montana State
University Western Agricultural Research Center,
580 Quast Lane, Corvallis, MT 59828
This project was funded by the Montana Specialty Crop
Block Grant AM200100XXXXG026. We thank Mon-
tana StateUniversity (MSU)-Bozeman and MSU-West-
ern Agricultural Research Center staff Amy Darling,
Haydon Davis, Kyrstan Hubbel, Ashley Kapus, Katrina
Mendrey, Kierstin Schmitt, Alex Hooglund, Shawna
Medlar, FrancesRafferty, Rebecca Richter, Olivia Soller,
and Andrea Ziolkowski for administrative and technical
support.WealsothanktheHortTechnologyeditors
and anonymous reviewers whose feedback greatly
improved the presentation of these results.
Mention of a trademark, proprietary product, or vendor
does not constitute a guarantee or warrant y of the prod-
uct by the U.S. Department of Agriculture and does
not imply its approval to the exclusion of other products
or vendors that also may be suitable.
R.L. is the corresponding author. E-mail: rachel.
leisso@montana.edu.
This is an open access article distributed under the
CC BY-NC-ND license (https://creativecommons.
org/licenses/by-nc-nd/4.0/).
https://doi.org/10.21273/HORTTECH04861-21
https://doi.org/10.21273/HORTTECH04861-21 1of8
limited and, due to breeding materials
originating from different locales, these
cultivars may have climate limitations
(Gerbrandt et al., 2017, 2018). There
are relatively few resources to guide
growers regarding cultivar selection,
plant management, and harvest param-
eters. In research plots near Elora and
Simcoe, Ontario, Canada, MacKenzie
et al. (2018) compared fruit weight,
yields, titratable acidity, pH, and solu-
ble solids content [SSC (12.4% to
17.9%)] of ve cultivars (Borealis,
Indigo Gem, Indigo Treat, Tundra,
Czech no. 17). They commented on
the difculty of determining harvest
timing because fruit color darkens
before maturity, making it challenging
to determine the optimum harvest
stage. In Poland, Ochmian et al.
(2012) performed multiple haskap fruit
harvests based on color for cultivars
Wojteck and Brazowa, with six and
seven harvests, respectively. The SSC
was lower for initial harvests (10.3%
and 9.6%, for Wojteckand Brazowa,
respectively) and higher for later har-
vests (14.1% and 12.6%), which they
attributed to higher temperatures later
in the season. Importantly, cultivars
compatible with a (one-pass) mechani-
cal harvest are a goal for the haskap
breeding program based at the Univer-
sity of Saskatchewan, Saskatoon, Sas-
katchewan, Canada (Bors et al., 2015).
In the rst several bearing years of
our cultivar comparison eld trial
(201719), we observed that certain
cultivars had substantial PHFD before
reaching our harvest maturity indices.
The PHFD phenomenon was also
documented by MacKenzie et al.
(2018), who indicated that applica-
tions of 0.02% hexanal did not mitigate
PHFD. Thompson (2006) also noted
variations in berry attachment to the
pedicel, which can be so tight that fruit
ruptures when harvested or so loose
that fruit falls before harvest. This
could be alternately interpreted as cul-
tivar-specic differences in abscission
regulation in relation to fruit maturity.
Preharvest dropped fruit are not only
lost yield but also a potential reservoir
for pests and diseases. Determining
which cultivars are prone to PHFD
would be important information for
guiding harvest management.
Relatively few treatments that
could alter preharvest drop rates have
been tested, and little has been reported
regarding abscission physiology to
inform the choices of products to test.
PGRscanbeusedtomitigatepreharv-
est drop of other fruit species, including
apple [Malus ×domestica (Robinson
et al., 2010)], plum [Prunus subgenus
Prunus sp. (Kaur et al., 2004)], and cit-
rus [Citrus sp.(Nawazetal.,2008)];
modes of action include delaying fruit
maturity via the ethylene biosynthesis
inhibiting aminoethoxyvinylglycine
[AVG (Layne et al., 2002)] and affect-
ing abscission physiology via a syn-
thetic auxin, 1-napthaleneacetic acid
[1-NAA (Nartvaranant, 2018)].
The objectives of our 2020 haskap
eld trials were to record PHFD rates
among haskap cultivars, collect at-har-
vest SSC to provide regional growers
with a baseline for comparison, and
test the utility of two PGRs for pre-
venting PHFD of two of the cultivars
previously observed to be susceptible.
Materials and methods
FIELD PLOTS.The haskap plant-
ing used for this project is located at
Montana State University Western
Agricultural Research Center (MSU-
WARC), Corvallis (lat. 4619045.500N,
long. 114507.400W). Most plants in
the research block were planted in
2015, although cultivars Boreal Bliz-
zard and Boreal Beauty were planted
in 2016 and 2018, respectively. Each
cultivar was planted in a randomized
complete block design, with three
blocks and three plants per cultivar per
block, with 3-ft in-row spacing and
12-ft spacing between rows. The
shrubs were not mulched and were
irrigated with drip emitters two to
three times per week originally at a rate
of 10 gal/week via a 1-gal/h pressure-
compensating emitter (Vortex Emitter;
Spot Systems, Santa Rosa, CA). As
plants increased in size, a second 1-
gal/hemitterwasaddedtoeachplant
at an increased distance from the plant
to accommodate the growing root sys-
tem. For the 2019 and 2020 growing
seasons, plants were irrigated at a rate
of 14 gal/week, with additional irriga-
tion during weeks when temperatures
above 90 F were maintained and
likely to led to plant stress. Weed man-
agement consisted of hand weeding
and spot spraying with glyphosate
(RoundUp; Bayer, Whippany, NJ) in
the rst year. After the rst growing
season, we added dormant applications
of granular pre-emergent herbicide
[dichlobenil (Casoron 4G; OHP,
Bluffton, SC)]; at a rate of 100 lb/
acre. Fertility management followed
standard recommendations for macro-
nutrients (nitrogen, phosphorus, and
potassium) in bush berries [e.g., saska-
toon serviceberry (Amelanchier alnifo-
lia) and blueberry (Miller et al.,
2021)]. Plants were protected with
bird netting [blue-green polyethylene
with 1-inch holes and reinforced
edges (SmartNet Systems; Comox,
BC, Canada)] beginning the rst week
of June, before external full color for
any haskap cultivars.
We collected data regarding
PHFD and assessed PGRs in Summer
2020. Air temperatures during harvest
(18 June23 July 2020) were higher
than typical, with average maximum
and minimum daily temperatures of
78 and 49 F, respectively. The only
major rainfall (2 inches) was recorded
between 28 and 30 June. Growing
degree-days [GDD (base 50 F, no
maximum, simple average calcula-
tion)] from 1 Jan. 2020 were 251
GDDon18June(rst harvest), and
754 GDD by 23 July (last harvest).
Temperature data used for these cal-
culations originated from the Corvallis
weather station located at MSU-
WARC, and GDD summaries were
calculated using an online phenology
and degree-day model (Integrated
Plant Protection Center at Oregon
State University, 2021).
PREHARVEST FRUIT DROP AND
HARVEST.To enable easy recovery of
dropped fruit, we placed lightweight
agricultural rowcover cloth on the
ground beneath one randomly selected
row per block for all haskap cultivars
and beneath all plants for Kawai and
Taka during the rst week of June.
Any berries that dropped from the
plants before harvest were gathered
and weighed weekly on a per-plant
basis. Fruit were harvested from indi-
vidual plants using a reciprocating saw
[variable speed (DCS381; DEWALT
Industrial Tool Co., Towson, MD)]
tted with an adapter (Quick-Change
Adapter/ReciproTools RCT-A10;
Jore Corp., Ronan, MT) with a pad-
ded U-shape attachment (custom
welded to a hex bit) to pummel
branches. Detached fruit dropped into
two large, angled catch trays with long
opposing bristles (6 inches) that
were placed on either side of the base
of the plant. We noted that some culti-
vars were becoming more prone to
2of8 https://doi.org/10.21273/HORTTECH04861-21
dropping fruit as the season pro-
gressed; even the slightest jostling of
branches to gather dropped fruit could
result in further drop. As a result, for
all harvests on and after 2 July 2020,
we collected dropped fruit from the
ground immediately after harvest and
weighed it to quantify lost yield.
Although we took great care not to
drop fruit on the ground during har-
vest, the PHFD data collected after
harvest may include a negligible num-
ber of berries lost during harvest
because of berries falling between the
bristles of the catch trays.
HARVEST INDICES.Samples of
berries on each plant were collected
and assessed approximately every 3 d
after external full color for SSC. Culti-
var harvest decisions were based on
the harvest indices of full blue ex-
terior color for all fruit, 14% SSC
(n = 27) combined with a subjective
cultivar-specic assessment of fruit a-
vor (performed by the same harvest
manager from preliminary harvests in
2016 through the end of the 2020
harvest season). The target SSC of
14% was established in 2017, when
repeated measurements of SSC after
external full color and subjective avor
evaluations revealed a continued in-
crease in SSC more than 14% and
improvement in avor after fruit had
developed full color.
SCC AT HARVEST.On the day of
harvest, 15 to 20 berries were col-
lected from each plant (representing
all sides and canopy positions of each
shrub) in the trial (for a total of 135
to 180 fruit per cultivar) and gently
placed in a small container. Sixty ber-
ries were randomly selected for mea-
suring SSC of the juice. Berries were
individually punctured with a 2-mm-
diameter probe and gently squeezed
to express the juice onto the lens of a
digital handheld refractometer (model
HI96801; HANNA Instruments,
Woodsocket, RI).
PILOT STUDY:PLANT GROWTH
REGULATORS TO PREVENT PREHARVEST
DROP.Treatments to prevent drop
were applied to cultivars Kawai and
Taka; these were chosen because of
prior observations of their propensity
for PHFD and their similar harvest
dates in prior years. We randomly
assigned one plant from each of three
blocks to each treatment (three plants
per treatment): an untreated control,
AVG (ReTain OL; Valent BioSciences,
Libertyville, IL) and 1-NAA (Fruitone
L; Amvac Chemical Co., Los Angeles,
CA). Per the manufacturersdirec-
tions, treatments were applied on 15
June, when fruit were nearing full size
and 50% of the berries were partially
blue color, and again on 10 July, 1
week before harvest on 16 July. Treat-
ments were applied using a 1-gal
manual sprayer (400 g1 G; Solo,
Newport News, VA) and applied to
one plant per block for cultivars Kawai
and Taka between 6:00 and 7:00 AM.
Both PGRs were applied at label rates
of 10 oz/acre in a volume of water
(3 L, 160 ppm PGR) previously deter-
mined to ensure full coverage of
plants. A nonionic surfactant (Rainier-
EA; Wilbur-Ellis, San Francisco, CA)
was used for 1-NAA and horticultural
oil (Wil-Gro Hort Oil 98-2, Wilbur-
Ellis) for AVG. Surfactants were used
at rates of 32 oz of nonionic surfac-
tant per 100 gal of spray (0.25%) and
1 gal of horticultural oil per 100 gal
water (1%). The same volume of water
was applied to control plants. Separate
hand pumps were used for each
treatment.
STATISTICS.Data were analyzed
with statistical analysis software (SAS
version 9.4; SAS Institute, Cary, NC).
Assumptions of normality were assessed
using the Shapiro-Wilk test statistic per-
formed with PROC UNIVARIATE
and homogeneity of variance with Lev-
enes test. For all analyses, post hoc
means separations were established per
Fishers least signicant difference at P
<0.05. Cultivar SSC, in-eld fruit
drop, yield, and related measures were
analyzed in PROC GLM. The SSC was
analyzed with a one-way Welchsanaly-
sis of variance (ANOVA) because of
the lack of homogeneity of variance
according to cultivar and the inability
to achieve homogeneity of variance
with transformations. Boreal Beauty
and Boreal Blizzardwere excluded
from yield-based comparisons because
these cultivars were planted later than
the main trial cultivars. For PGR appli-
cations, data were analyzed with PROC
GLM with the factors of cultivar and
treatment. Boxplots were generated by
the open-source statistical analysis and
data visualization software (R Founda-
tion for Statistical Computing, Vienna,
Austria) with the tidyverse (Wickham
et al., 2019) and ggplot2 (Wickham,
2009) packages. Because PGR applica-
tion effects on preharvest drop were
not signicant, we performed a power
analysis using G*Power (Faul et al.,
2009) to determine the power and
effect size (for one-way ANOVA
according to the cultivar) based on the
preharvest drop as well as yield lost to
preharvest drop (percent) means and
SDs for each treatment for Kawai and
Taka. We further estimated the recom-
mended sample size for future studies
basedontheeffectsize.
Results
The rst haskap harvest was 18
June 2020 (Sugar Mountain Blue),
and the last harvest was 23 July 2020
(Kapu) (Table 1). Warmer tempera-
tures before and during harvest resul-
ted in a shorter harvest season than
that during previous years. Borealis
and Boreal Blizzard’—which have
been harvested typically in Julywere
harvestedinJune.
Cultivars differed in marketable
yield, yield potential, and percent of
yield potential lost to PHFD (Table
2). Marketable yields (fruit remaining
on the plant at harvest) and yields
(marketable yield plus PHFD) repre-
sent only plants for which PHFD data
were also collected (n = 3). Market-
able yields 6 years after planting
ranged more than 12-fold, from 609
to 7648 g/plant. Unnamed cultivar
85-19 had the highest marketable
yield, followed by Tana (5676 g/
plant). The earliest ripening cultivars,
Blue Goose, Sugar Mountain Blue,
and Wild Treasure, had generally lower
yields (<800 g/plant) than later-
Table 1. Harvest dates for haskap cul-
tivars in 2020 at Corvallis, MT.
Cultivar Harvest date
Aurora 2 July 2020
Blue Goose 19 June 2020
Boreal Beauty 6 July 2020
Boreal Blizzard 26 June 2020
Borealis 24 June 2020
Chito 11 July 2020
Indigo Gem 22 June 2020
Kapu/SOLO
z
23 July 2020
Kawai 20 July 2020
Keiko 20 July 2020
Sugar Mountain Blue 18 June 2020
Taka 16 June 2020
Tana 20 July 2020
Wild Treasure 19 June 2020
85-19
y
9 June 2020
z
SOLO is the name trademarked by Spring Meadow
Nursery, Grand Haven, MI.
y
An unnamed cultivar by Dr. Maxine Thompson.
https://doi.org/10.21273/HORTTECH04861-21 3of8
ripening cultivars. Yields for 85-19
(7946 g/plant) and Tana(5809 g/
plant) were greater than those for
most cultivars, followed by Kawai
(4774 g/plant), which was nominally
higher but not signicantly different
from the yields of Chito (3603 g/
plant) and Kapu. The next three high-
est-yielding cultivars were Aurora,
Borealis, and Keiko, with 3200 g/
plant.
The cultivars with the highest
percentage of yield lost to PHFD
were Kawai (47.6%), Taka (43.6%),
and Chito (42.5%) (Table 2). Boreal
Beautyand Keikoyield losses
(both 30%) were not statistically
different from Boreal Blizzardand
Kapu(both 12%). Cultivars with
the lowest yield lost to PHFD were
Tana (2.8%), Sugar Mountain Blue
(1.6%), Indigo Gem (1.2%), Borealis
(1.2%), and Blue Goose (1.0%). After
comparing the marketable yield to the
yield changes, the top ve highest-
yielding cultivars were 85-19, Tana,
Aurora, Borealis, and Kapu (market-
able yield), and 85-19, Tana, Kawai,
Chito, and Kapu (yield).
At-harvest SSC (for fruit remain-
ing on plants) varied among cultivars,
with Kapu at the high end (18.4%)
and Boreal Beauty at the low end
(13.0%) (Table 2).
In our pilot study, PHFD (as
measured by the percent of yield
potential) was not signicantly inu-
enced by PGR treatment (Fig. 1). A
follow-up statistical analysis (power
analysis) indicated the experiment was
underpowered, with the power (1-b)
of present results being between 0.07
and 0.37 according to the dependent
variable and cultivar. Recommended
samples sizes for future work, assum-
ing similar experimental conditions,
are between 48 and 207 plants or,
assuming one control and two PGR
treatments, between 16 and 70 plants
per treatment.
Discussion
Haskap has only recently been
bred and cultivated as a commercial
berry crop in North America. Predilec-
tion to PHFD could be an important
factor in cultivar selection and manage-
ment.Littletonoresearchofhaskap
PHFD has been performed to compare
cultivars, understand its physiological
basis, and manage the phenomenon.
Although the present data are limited in
terms of plant numbers and represent
one eld season, the lack of harvest in-
dices for specic cultivars complicates
the study beyond simply gathering an
additional year of data of PHFD. We
share these preliminary results for
cultivar comparison of PHFD to
enhance the research of establishing
harvestindicesaswellasPHFDman-
agement, and we further include pilot
study results involving PGRs intended
to prevent fruit drop of haskap.
MARKETABLE YIELDS.Because
most cultivars were 6 years old in
2020, the plants would have been
approaching mature yields (Hummer,
2006). We excluded Boreal Blizzard
and Boreal Beautyfrom our yield-
related analyses because we planted
them one and three growing seasons
later, respectively, than the other cul-
tivars in the trial were planted. Our
yield data represent only plants for
which we also recorded PHFD; fur-
ther yield information is available on
the MSU-WARC website (Z. Miller
and B. Jarrett, unpublished data).
PREHARVEST FRUIT DROP.Culti-
vars Kawai, Chito, and Taka exhibited
PHFD of 40% to 50% loss of the poten-
tial yield per plant. Because of low plant
numbers and variability in drop and
yield, Boreal Beautyand Keiko
PHFD yield losses of 30% did not dif-
fer signicantlyfromthoseofBoreal
Blizzardand Kapu, which had nomi-
nally lower yield losses to PHFD of
11.7% and 10.8%, respectively. Al-
though we do not have quantitative
data regarding PHFD from prior years,
Table 2. Marketable yield, yield, percent yield lost to preharvest fruit drop (PHFD), and individual haskap berry soluble
solids content (SSC) in haskap cultivars in 2020 at Corvallis, MT. Yield data are excluded for Boreal Blizzardand Boreal
Beautybecause they were planted 1 and 3 years later, respectively, than the other cultivars in the trial.
Cultivar
Marketable yield (g)
z
Yield (g)
y
Yield lost to PHFD (%)
x
SSC (%)
mean ± SE
Aurora 3201 ± 721 bc
w
3332 ± 738 cde
w
4.0 ± 0.94 cd
w
15.5 ± 0.19 cde
v
Blue Goose 654 ± 132 e 661 ± 133 f 1.0 ± 0.02 f 14.4 ± 0.21 f
Boreal Beauty Not reported Not reported 30.5 ± 3.31 ab 13.0 ± 0.32 g
Boreal Blizzard Not reported Not reported 11.7 ± 3.60 bc 14.8 ± 0.18 def
Borealis 3151 ± 248 abc 3188 ± 253 cde 1.2 ± 0.54 ef 14.5 ± 0.15 ef
Chito 2170 ± 744 c 3603 ± 882 cd 42.5 ± 5.84 a 14.6 ± 0.17 ef
Indigo Gem 1626 ± 334 cd 1642 ± 332 ef 1.2 ± 0.41 ef 15.8 ± 0.32 cd
Kawai 2452 ± 283 bc 4774 ± 768 bc 47.6 ± 3.35 a 14.6 ± 0.17 ef
Keiko 2572 ± 1089 c 3162 ± 796 cde 29.9 ± 22.37 ab 17.3 ± 0.21 ab
Kapu 3070 ± 261 bc 3443 ± 265 cd 10.8 ± 3.37 bc 18.4 ± 0.27 a
Sugar Mountain Blue 759 ± 211 de 772 ± 216 f 1.6 ± 0.27 def 16.2 ± 0.27 bc
Taka 1603 ± 270 cd 2865 ± 186 de 43.6 ± 9.42 a 14.2 ± 0.34 f
Tana 5676 ± 978 ab 5809 ± 1018 b 2.8 ± 0.34 def 14.5 ± 0.21 ef
Wild Treasure 609 ± 232 e 634 ± 225 f 7.1 ± 4.89 cd 15.3 ± 0.25 cdef
85-19 7648 ± 728 a 7946 ± 824 a 3.6 ± 0.76 cde 16.1 ± 0.19 c
z
Mean per-plant weight of all fruit harvested from plants within a cultivar; 1 g = 0.0353 oz.
y
Marketable yield 1mean per-plant weight of PHFD within a cultivar.
x
(PHFD yield) × 100.
w
Means (n = 3 plants) in a column followed by the same lowercase letter are not signicantly different (Fishers least signicant difference test at P<0.05).
v
Means (n = 60 berries) in a column followed by the same lowercase letter are not signicantly different (Welchs one-way ANOVA); we used Welch's one-way ANOVA
due to the lack of homogeneity of variance among cultivars.
4of8 https://doi.org/10.21273/HORTTECH04861-21
the cultivars found to have high PHFD
were consistent with prior observa-
tions. However, Boreal Beautywas
planted in 2018, and the fact these
plants were younger than the others
should be taken into consideration
when interpreting results. Despite high
PHFD rates, some cultivars (i.e.,
Kawai) still had relatively high market-
able yields (2452 g/plant). More than
half the cultivars in our trial exhibited
reasonably low yield lost to PHFD (3%
to 12% of yield). Notably, unnamed
cultivar 85-19 had the highest market-
able yield and a low percentage of yield
lost to PHFD (3.6%). Cultivars Blue
Goose, Wild Treasure, and Sugar
Mountain Blue had low PHFD; how-
ever, these cultivars are not likely to be
well-suited for commercial production
in Montana because of susceptibility to
early (JanuaryFebruary) budbreak and
subsequent cold injury, small fruit, low
yields, and unpalatable bitterness.
Preharvest fruit drop may be
attributable to cultivar-specicregula-
tion of fruit abscission combined with
uneven maturity, with some cultivars
dropping berries at or near maturity
and others retaining mature fruit lon-
ger. Similar phenomena occur in other
commercial fruit species and can be
different according to cultivar. For
example, the apple cultivar McIntosh
is extremely prone to fruit drop near
maturity (Robinson et al., 2010),
whereas other cultivars are less so (e.g.,
Empire, Gala, Fuji) (Irish-Brown et al.,
2011). Supporting the hypothesis of
uneven fruit maturity, in haskap foun-
dation germplasm, Gerbrandt et al.
(2017) documented extended bloom
durationaswellasstaggeredexternal
color development. We have made
similar observations regarding bloom
and external berry color development
in our haskap eld trial (Z. Miller and
B. Jarrett, unpublished data).
Additional conditions associated
with PHFD in other fruit species in-
clude malnutrition, water stress, pests,
disease (Nawaz et al., 2008), heat
stress (Robinson et al., 2010), and
high winds (van Rhee, 1958). In our
study, PHFD was concentrated in
later-season cultivars for which higher
temperatures could have contributed
to heat stress leading to PHFD,
although some later-season cultivars
(e.g., Tana and Kapu) still had low lev-
els of PHFD. Plants in our trial
received the same quantity of water via
drip irrigation, but it is possible that
cultivars have differing water needs,
and that cultivars with high PHFD
needed more water than was provided.
However, no symptoms of water or
heat stress (leaf wilting or curling)
were observed for any cultivars in our
trial. Similarly, the plants experienced
no pest or disease problems, no
extreme winds before harvest, and no
extensive PHFD after several rainy
days at the end of June.
HARVEST MANAGEMENT AND
PHFD. The simplest method to
reduce yield lost to PHFD would be to
harvest before or when fruit drop is rst
noted, assuming all berries on a plant
have attained full exterior blue color.
Gerbrandt et al. (2020) harvested 3 to
5 d after all fruit on the shrub reached
full color. The SSC in their study were
lower than those reported in the pre-
sent work, but the location and cultivar
differences between our studies con-
found any interpretation of lower SSC
in relation to avor or eating quality.
As discussed, our experience recom-
mends against harvesting solely based
on exterior color, but we have no data
regarding product quality or fresh fruit
consumer preference with which to val-
idate these concerns.
Alternately, cultivars prone to
PHFD may be best-suited to backyard
growers or fresh market operations
where fruit can be hand-harvested mul-
tiple times. However, where unevenness
in fruit maturity exists, determining
optimal ripeness may be problematic, as
discussedinrelationtoharvestindices.
SSC AND OTHER PROPOSED
HARVEST INDICES.In the present
study, SSC (along with full fruit color
and the subjective avor evaluation)
was one of the primary harvest indices.
The SSC is a commonly used horticul-
tural maturity index for many types of
fruit (Reid, 2002). Optimal SSC can
vary widely among cultivars within a
species, and the present study illus-
trates the challenges of applying a uni-
form harvest index across cultivars
within a novel fruit crop, with the
summary concern being that delaying
harvest to achieve higher SSC led to
higher PHFD in some cultivars in our
Fig. 1. A pilot trial using plant growth regulators (PGRs)
aminoethoxyvinylglycine (AVG) and 1-napthaleneacetic acid (1-NAA) did not
demonstrate any inuence of PGRs on preharvest fruit drop (PHFD) rates for
haskap cultivars Kawai and Taka. PGRs were each applied at a rate of 10 oz/
acre (160-ppm solution in water to thoroughly coat plants) with a nonionic
surfactant and horticultural oil, respectively, when 50% of the berries were
partially blue (15 June 2020) and 1 week before harvest (10 July 2020). Control
plants were sprayed with the same volume of water as treatments. Percent yield
lost to PHFD [weight of berries dropped preharvest 4(weight of berries dropped
preharvest + yield harvested from the plant at commercial maturity) × 100] did
not differ according to treatments. Each boxplot represents three plants indicated
by the points. 1 oz/acre = 0.0731 Lha
21
; 1 ppm = 1 mgL
21
.
https://doi.org/10.21273/HORTTECH04861-21 5of8
study. However, because PHFD does
not appear to be explicitly tied to high
SSC based on the present data, culti-
vars likely vary in the optimal SSC at
harvest.
Limited information is available
regarding SSC specic to a given haskap
cultivar at optimal maturity, and when
it is reported, it is typically not described
in the context of harvest management
for fruit avor or quality. MacKenzie
et al. (2018) compared SSC (values
from 12.4% to 17.9%) along with other
fruit characteristics at harvest for ve
cultivars (Borealis, Indigo Gem, Indigo
Treat,Tundra,Czechno.17).Intheir
study, SSC reported at harvest varied
among cultivars, locations, and years.
Our data include only two of the same
cultivarsBorealisandIndigoGem
and their SSCs in 2020 had similar
ranges. Borealisand Indigo Gem
had SSC of 8.7% and 12.4%, respec-
tively, according to research by Ger-
brandt et al. (2020), and Chito,
Kapu,Kawai,Keiko,andTana
had SSCs between 13.0% and 14.6%
listed in their patents (Thompson
2016a, 2016b, 2016c, 2016d, 2017a,
2017b). However, the climates in
which this information was collected are
quite different from that of Montana
(temperate coastal with mild winters
and cool summers in Fraser Valley, Brit-
ish Columbia, Canada, compared to
continentalwithcoldwintersandhot
summers). Climate can affect SSC,
along with many other aspects of berry
quality (Barnuud et al., 2014).
The other harvest indices we com-
bined with SSC were color (all fruit on
a shrub must have full blue exterior
color) and avor evaluation, the latter
of which is difcult to measure quanti-
tatively and communicate effectively.
In our rst harvest season (2017), we
harvested based on surface color alone
(exterior fruit color having changed
from green to blue) and found the fruit
to be extremely tart and sour, and the
overall avor to be greenand unap-
pealing. Our conclusion was that,
unlike many other berries, the exterior
color of haskap fruit changes from
green to blue before fruit reaches horti-
cultural maturity (dened as optimum
eating quality) (Reid, 2002) according
to our observations and those of Mac-
Kenzie et al. (2018). The sour taste we
noted could likely be approximated by
titration (Da Conceicao Neta et al.,
2007). Titratable acidity as well as the
ratio of SSC to titratable acidity are
used for other fruit crops as harvest
indices (Reid, 2002). These indices
may be best considered in a climate-
region specic manner, and we recom-
mend that growers and researchers
should track and share these measures
in relation to avor and other fruit
quality aspects to support the possible
establishment of these parameters as
harvest indices in their region.
PLANT GROWTH REGULATOR
INFLUENCE ON PREHARVEST FRUIT
DROP.Applying 1-NAA and AVG
twice, with the last application 1 week
before harvest, had no statistically sig-
nicant inuence on PHFD rates for
cultivars Kawai and Taka. Because of
our eld trial size, treatments were
applied to only one plant per block,
for a total of three plants per treat-
ment. The follow-up power analysis
indicated this experiment was under-
powered; therefore, we consider this a
pilot study and the results should be
considered primarily to guide future
PGR work. Based on the power analy-
sis, the recommended numbers of
plants (divided into three treatment
groups) are between 48 and 207,
depending on the dependent variable
(PHFD or PHFD relative to total
potential yield) and cultivar (Kawai
and Taka). However, we are unaware
of any local growers who have planted
these cultivars in larger quantities than
those in our eld trial.
When attempting to mitigate has-
kap PHFD, we chose to test two com-
mercially available PGRs that are
commonly used in the fruit industry.
However, these PGRs are typically used
for fruit crops in the plant families
including apple and plum (Rosaceae),
grape (Vitaceae), and citrus (Rutaceae),
whereas haskap is in the honeysuckle
(Caprifoliaceae) family. Biochemical
maturation and abscission physiology
in haskap may differ enough that these
PGRs do not have the intended effect.
This points to the need for research of
physiological mechanisms of haskap
fruit maturity and abscission to inform
selection or development of effective
stop-drop treatments. However, even
in fruit crops (e.g., apple) for which
maturation and abscission physiology
are relatively well understood, the ability
of PGRs to reduce PHFD can vary
according to treatment quantity and ti-
ming, cultivar, and other environmental
or management factors (Schwallier and
Irish-Brown, 2014). Therefore, opti-
mizing application timing or rates for
specic PGRs may assist their effective-
ness in minimizing haskap PHFD.
Conclusions
Preharvest drop of haskap fruit
varied among cultivars, with Kawai,
Chito, and Taka presenting the high-
est PHFD, although marketable yields
for some cultivars (especially Kawai)
were still within the range of other
cultivarswithhighmarketableyield
and lower PHFD rates. Approxi-
mately half of the cultivars had PHFD
ratesthatwerelessthan5%ofthe
potential yield. These results are based
on 1 year of data. Because of the lim-
ited information available about the
North American cultivars for this
novel fruit crop, harvest timing may
not have coincided with optimal har-
vest indices for the cultivars in our
trial, resulting in higher PHFD than
may be expected if fruit are harvested
at different harvest indices. Currently,
the simplest route to reduce PHFD
yield loss in these cultivars is harvest-
ing earliermost likely before the tar-
get SSC level in this trial, which was
14% SSC. It is necessary to develop
additional simple harvest indices and
cultivar-specic harvest management
guidelines for haskap, which could
prove challenging because of the
plethora of cultivars available and the
varied locations and environments
with which haskap production may be
compatible. We present our prelimi-
nary PHFD results and SSC at harvest
to contribute to these efforts, which
may be best performed in a region-
specicmanner.
Using 1-NAA and AVG in an
attempt to prevent PHFD for cultivars
Kawai and Taka did not result in a sta-
tistically signicant effect on PHFD
rates, but we share the results as those
of a pilot study with the intent that
they may be useful to any future PGR
research to mitigate PHFD.
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Article
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Blue honeysuckle (Lonicera caerulea L.) is a northern-adapted crop species with extremely early phenology and cold hardiness. Restricted adaptation to temperate climates is a current limitation to the crop’s mainstream potential for large-scale production. Based on the broad germplasm base at the University of Saskatchewan, vegetative growth cessation and leaf drop phenology were characterized to complement analysis of spring phenological adaptation in a temperate climate. A multi-trial site of three foundation groups and a single-site trial of three improved groups compared with their parental foundation genotypes were conducted in the Fraser Valley, British Columbia, Canada in 2012 and 2013. The current study shows that blue honeysuckle germplasm contains considerable phenological variation that will permit adaptation to temperate climates. It also demonstrates that breeding for improved adaptation is possible using the existing germplasm resources. For Russian germplasm with the earliest phenology, adaptation to northern latitudes and short growing seasons results in early floral initiation, which presents an indirect limitation to production in more southern latitudes due to secondary flowering. Early leaf drop indirectly limits production and is related to poor adaptation to high chill environments. Skew toward later leaf drop in improved groups, produced from hybridization with Japanese and Kuril germplasm with intermediate and late phenologies, respectively, shows that development of better adaptation to southern latitudes can be achieved.
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Growers are challenged to provide premium, ripe haskap fruit to market while limiting the negative attributes associated with over-ripening. Hexanal is an inhibitor of phospholipase D, an enzyme involved in membrane degradation, and has shown promise in extending the longevity of fruit. This study investigated the performance of a hexanal-based preharvest spray for enhancing the quality and shelf life of haskap fruit, an emerging crop in Canada. At two locations in 2015, 2016, and 2017, five cultivars were sprayed with a control treatment or a 0.02% hexanal formulation at 2–3 wk before harvest. Fruit was stored at 4 °C and assessed for quality at successive times. Although inconsistent, results suggest a hexanal spray may impart a small benefit to the postharvest quality of haskap fruit. Secondary objectives included describing important agronomic characteristics of haskap and assessing the potential of a hexanal preharvest spray for enhancing fruit retention. Hexanal did not reduce fruit drop and had no effect on quality at harvest. Fruit contained high levels of soluble solids and titratable acids, were very dark in colour, and did not degrade in quality as rapidly as softer fruit crops such as strawberry or raspberry.
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Blue honeysuckle (Lonicera caerulea L.) is a novel fruit crop that stands out for its northern climatic adaptation. Understanding spring phenological adaptation to temperate climate is central to development of a broader range of production and greater mainstream crop potential. In 2012 and 2013 across three sites in the Fraser Valley, British Columbia, spring phenophases from bud break to fruit harvest were determined across three foundation groups. Genetic variability is characterized for Russian, Japanese, and Kuril blue honeysuckle foundation groups used in breeding at the University of Saskatchewan, Saskatoon, SK. Germplasm group membership is the principal feature of phenological adaptation. Although temperate climate adaptation is limited in the Russian germplasm, the intermediate Japanese and later Kuril spring phenology provide an adequate degree of temperate climate adaptation to facilitate commercial production. These findings demonstrate that blue honeysuckle has phenological adaptation to a temperate climate. Diversity between and within genetic groups presents opportunities for crop enhancement, especially through breeding for later bloom periods.