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1 New Zealand Winegrowers I nzwine.com
INTRODUCTION
Spring frosts are an annual possibility in almost
all major winegrowing regions of New Zealand
so it makes sense that frost protection should be
incorporated into the routine annual management of
almost every vineyard.
Many experts have noted that the best time
to protect a vineyard against frost is before it
is established. Site selection can be one of the
most critical times for determining a vineyard’s
susceptibility to frost damage. Locating a vineyard
away from areas where cold air ponds, on hillsides
or close to coastal areas can all help in reducing
potential frost risk. If you are looking at establishing
a vineyard and have several options available for
consideration, a 1999 New Zealand Winegrowers’
report provides valuable information on how to
evaluate the frost risk of a site. 1
The present guide, however, reviews the current
options available to New Zealand growers once a
site is established, including:
• Frost forecasting.
• Vineyard monitoring and alarm systems.
• Passive frost protection (actions taken in the
vineyard prior to a frost).
• Active frost protection (including helicopters,
frost fans, water systems and heaters).
• Frost damage mitigation.
• Links to additional resources on New Zealand
Winegrowers’ website (www.nzwine.com).
A short booklet like this can summarise current
best practice, but it cannot provide the level of
technical detail required before making a substantial
investment in a frost protection system. Given the
financial implications of failures in frost protection,
it is important to seek qualified advice before
investing in or relying on any method for protecting
your crop against frost.
TABLE OF CONTENTS
1. TYPES OF FROST Radiation
Advection
Other types
2. CRITICAL TEMPERATURES AND VINE DEVELOPMENT
Growth stage vulnerability to frost
Critical temperature
Defining frost severity
Environmental conditions
3. FROST FORECASTING On-site weather stations and alarm systems
Regional forecasts
Calibrating vineyard temperatures
Calculating risk
4. FROST CONTROL METHODS Passive methods – cultural inputs
Active methods
• Heaters
• Wind mixing (helicopters, frost fans)
• Water systems (overhead and other sprinkler
systems)
5. REDUCING FROST DAMAGE Assessment of damage
Damage in spring
Options for management
Appendix: New Zealand Winegrowers Frost Fan Code of Practice 2014
1 Trought MCT, Howell GS and Cherry N. 1999. Practical Considerations for Reducing Frost Damage in Vineyards. Report to New Zealand Winegrowers.
2 New Zealand Winegrowers I nzwine.com
Figure 1-1. As cold air stays low and warm air rises, the air becomes stratified and
a temperature inversion forms.
ADVECTION FROSTAdvection is the horizontal movement of an air
mass. If the air mass is below 0 °C, an advection
frost results. In New Zealand, advective frosts
generally occur when a cold polar air mass
moves north over the country. They are generally
characteristic of continental climates in New
Zealand. Some radiation frosts can have an
advective component.
OTHER FROST TYPESGROUND FROST
• Occurs when dew freezes.
• Requires a grass minimum temperature of -1 °C or
less.
• Young vines are most vulnerable to ground frost.
SCREEN FROST
• Screen refers to a Stevenson Screen,2 placed
approximately 1.3 metres above ground level –
generally just above cordon height for most New
Zealand vine training systems.
• Screen frost occurs when air temperature at and
below screen height is 0 °C or less.
HOARFROST
• Central South Island only.
• Occurs over a period of days when daytime
temperatures are not warm enough to defrost the
previous night’s frost and another frost occurs.
• Ice crystals form from water vapour, without
going through a liquid phase.
COOL AIR
3o
2o
1o
0o
-1o
-2o
WARMER AIR
I – TYPES OF FROST
Vineyard management in New Zealand focuses on
two types of frost:
1. Radiation frost
(the most common type encountered).
2. Advection frost.
RADIATION FROSTRadiation frosts occur widely throughout New
Zealand. After sunset, when the sky is colder than
the ground, ground temperature will drop and heat
will be transferred (radiated) to the sky above.
When temperatures fall enough, a radiation frost
will occur – often, during clear, settled weather with
light surface winds. Cold air is heavier than warm
air and will settle in areas of lower elevation. As
the cold air stays low and the warm air rises, the
air becomes stratified and a temperature inversion
forms.
Radiation frost is characterised by this inversion
layer and usually a katabatic (downslope) drift.
INVERSION LAYER
The inversion layer can range from five metres to
several hundred metres above ground, although
usually the range falls between 10 to 30 metres.
An inversion can have considerable spatial
variation, and inversion strengths are a function
of topography, katabatic wind speeds and the
moisture content of the air and ground.
It is the inversion layer that is used by helicopters
and frost fans, which move the warm air from the
inversion layer downwards to raise the temperature
of the air around the vines.
KATABATIC DRIFT
Another common characteristic of a radiation frost
are katabatic winds. This is the technical name for
a downward, cooling wind that carries cold air from
a higher elevation down a slope under the force of
gravity. In some instances it is possible to physically
feel the cool katabatic winds as you stand in a
vineyard on an otherwise still, calm night.
3 New Zealand Winegrowers I nzwine.com
Figure 1-2. Hoarfrost at Akarua in Central Otago.
MORE RESOURCES ON NZWINE.COM:Introduction to frost – New Zealand Winegrowers Fact Sheet
Radiation and advection frosts – New Zealand Winegrowers Fact Sheet
Climate and frost risk – New Zealand Winegrowers Fact Sheet
References
• Trought MCT, Howell GS and Cherry N. 1999. Practical Considerations for Reducing Frost Damage in
Vineyards. Report to New Zealand Winegrowers.
2 A Stevenson screen is an enclosure to shield meteorological instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely. It forms part of a standard weather station.
4 New Zealand Winegrowers I nzwine.com
II – CRITICAL TEMPERATURES & VINE DEVELOPMENT
Spring frosts are the likeliest to cause damage if a
vineyard is unprotected.
• Critical temperatures are relative to growth
stage(s) of the vine and severity of frost.
• The more advanced the phenological stage (at
least up to flowering) the more susceptible the
grapevine is to frost damage.
Spring frosts can reduce yields and threaten
vineyard productivity, not only for the oncoming
season but also in subsequent years. If one or more
frosts occurs during a susceptible period in the
grapevine’s growing cycle, then crop loss can be
significant.
HOW DOES DAMAGE OCCUR?Dense cold air flows downward into the vineyard.
Frost temperatures cause damage by freezing the
sap inside the conducting vessels of the grapevine.
As the sap freezes, it expands, causing cell walls to
rupture. This can result in tissue damage to leaves,
shoots, buds and vascular tissue. Once the cell wall
has ruptured in Vitis vinifera, it doesn’t repair itself
(unlike other plants).
SEASONAL RISKS
Spring
Swelling grapevine buds or young shoots are
damaged or destroyed when temperatures fall
below critical values for a prolonged period of
time. Damage can affect the current season’s crop,
and can also influence vine productivity in future
seasons.
Autumn
Frost before harvest can cause premature leaf
fall. This may affect vine performance in the
next season, particularly if vines are young. If
the frost is very early, it can prevent wood fully
maturing, leading to decreased tolerance of lower
winter temperatures due to poor carbohydrate
development and storage.
DEFINING SPRING FROSTS BY GROWTH STAGE
Spring frosts can be divided into three subgroups
based on growth stages as categorised by the
Modified Eichhorn-Lorenz (E-L) Phenological
System:
• Early Spring – occurring from E-L 2 (bud scales
opening) to E-L 11 (4 leaves separated, shoots 6-8
cm long).
153
V I T I C U L T U R E 1 : R E S O U R C E S
Figure 7.3 Modified E-L system for identifying major and intermediate grapevine growth stages (revised from Coombe 1995). Notethat not all varieties show a woolly bud or a green tip stage (May 2000) hence the five budburst stages in the modified original 1995system have been changed slightly by removing stage 4 and allocating the definition of budburst to what was formerly stage 5.Revised version of “Grapevine growth stages – The modified E-L system” Viticulture 1 – Resources. 2nd edition 2004. Eds. Dry, P. and Coombe, B.(Winetitles)
1 Winter bud
2 Bud scales opening
3 Wooly bud ± green showing
4 Budburst; leaf tips visible
7 First leaf separated from shoot tip
9 2 to 3 leaves separated; shoots 2-4 cm long
11 4 leaves separated
12 5 leaves separated; shoots about 10 cm long;inflorescence clear
13 6 leaves separated
14 7 leaves separated
15 8 leaves separated, shoot elongating rapidly;single flowers in compact groups
16 10 leaves separated17 12 leaves separated; inflorescence well
developed, single flowers separated18 14 leaves separated; flower caps still in place,
but cap colour fading from green19 About 16 leaves separated; beginning of
flowering (first flower caps loosening)
20 10% caps off
21 30% caps off
23 17-20 leaves separated; 50% caps off (= flowering)
25 80% caps off
26 Cap-fall complete
27 Setting; young berries enlarging (>2 mmdiam.), bunch at right angles to stem
29 Berries pepper-corn size (4 mm diam.);bunches tending downwards
31 Berries pea-size (7 mm diam.)
32 Beginning of bunch closure, berries touching(if bunches are tight)
33 Berries still hard and green
34 Berries begin to soften;Sugar starts increasing
35 Berries begin to colour and enlarge
36 Berries with intermediate sugar values
37 Berries not quite ripe
38 Berries harvest-ripe
39 Berries over-ripe
41 After harvest; cane maturation complete
43 Beginning of leaf fall
47 End of leaf fall
4 Budburst
Inflorescence clear,5 leaves separated
50% caps off
Young berries growingBunch at right angles to stem
Bunches hanging down
Berry softening continuesBerry colouring begins
Berries ripe
12 Shoots 10 cm
19 Flowering begins
23 Flowering
27 Setting
31 Berries pea-size
35 Veraison
38 Harvest
Sh
oot
and
inflo
rescence
develo
pm
ent
Flo
werin
gB
erryfo
rmatio
nB
erryrip
enin
gSen
escence
MAJOR STAGES ALL STAGESE-L number
Viti 1 Chapter 07 Phenology 27/9/05 10:18 AM Page 153
• Mid Spring – occurring from E-L 12 (5 leaves
separated, shoots about 10 cm long, inflorescence
clear) to E-L 14 (7 leaves separated).
153
V I T I C U L T U R E 1 : R E S O U R C E S
Figure 7.3 Modified E-L system for identifying major and intermediate grapevine growth stages (revised from Coombe 1995). Notethat not all varieties show a woolly bud or a green tip stage (May 2000) hence the five budburst stages in the modified original 1995system have been changed slightly by removing stage 4 and allocating the definition of budburst to what was formerly stage 5.Revised version of “Grapevine growth stages – The modified E-L system” Viticulture 1 – Resources. 2nd edition 2004. Eds. Dry, P. and Coombe, B.(Winetitles)
1 Winter bud
2 Bud scales opening
3 Wooly bud ± green showing
4 Budburst; leaf tips visible
7 First leaf separated from shoot tip
9 2 to 3 leaves separated; shoots 2-4 cm long
11 4 leaves separated
12 5 leaves separated; shoots about 10 cm long;inflorescence clear
13 6 leaves separated
14 7 leaves separated
15 8 leaves separated, shoot elongating rapidly;single flowers in compact groups
16 10 leaves separated17 12 leaves separated; inflorescence well
developed, single flowers separated18 14 leaves separated; flower caps still in place,
but cap colour fading from green19 About 16 leaves separated; beginning of
flowering (first flower caps loosening)
20 10% caps off
21 30% caps off
23 17-20 leaves separated; 50% caps off (= flowering)
25 80% caps off
26 Cap-fall complete
27 Setting; young berries enlarging (>2 mmdiam.), bunch at right angles to stem
29 Berries pepper-corn size (4 mm diam.);bunches tending downwards
31 Berries pea-size (7 mm diam.)
32 Beginning of bunch closure, berries touching(if bunches are tight)
33 Berries still hard and green
34 Berries begin to soften;Sugar starts increasing
35 Berries begin to colour and enlarge
36 Berries with intermediate sugar values
37 Berries not quite ripe
38 Berries harvest-ripe
39 Berries over-ripe
41 After harvest; cane maturation complete
43 Beginning of leaf fall
47 End of leaf fall
4 Budburst
Inflorescence clear,5 leaves separated
50% caps off
Young berries growingBunch at right angles to stem
Bunches hanging down
Berry softening continuesBerry colouring begins
Berries ripe
12 Shoots 10 cm
19 Flowering begins
23 Flowering
27 Setting
31 Berries pea-size
35 Veraison
38 Harvest
Sh
oot
and
inflo
rescence
develo
pm
ent
Flo
werin
gB
erryfo
rmatio
nB
erryrip
enin
gSen
escence
MAJOR STAGES ALL STAGESE-L number
Viti 1 Chapter 07 Phenology 27/9/05 10:18 AM Page 153
• Late Spring – occurring from E-L 15 (8 leaves
separated, shoot elongating rapidly) to E-L 25
(80% caps off).
153
V I T I C U L T U R E 1 : R E S O U R C E S
Figure 7.3 Modified E-L system for identifying major and intermediate grapevine growth stages (revised from Coombe 1995). Notethat not all varieties show a woolly bud or a green tip stage (May 2000) hence the five budburst stages in the modified original 1995system have been changed slightly by removing stage 4 and allocating the definition of budburst to what was formerly stage 5.Revised version of “Grapevine growth stages – The modified E-L system” Viticulture 1 – Resources. 2nd edition 2004. Eds. Dry, P. and Coombe, B.(Winetitles)
1 Winter bud
2 Bud scales opening
3 Wooly bud ± green showing
4 Budburst; leaf tips visible
7 First leaf separated from shoot tip
9 2 to 3 leaves separated; shoots 2-4 cm long
11 4 leaves separated
12 5 leaves separated; shoots about 10 cm long;inflorescence clear
13 6 leaves separated
14 7 leaves separated
15 8 leaves separated, shoot elongating rapidly;single flowers in compact groups
16 10 leaves separated17 12 leaves separated; inflorescence well
developed, single flowers separated18 14 leaves separated; flower caps still in place,
but cap colour fading from green19 About 16 leaves separated; beginning of
flowering (first flower caps loosening)
20 10% caps off
21 30% caps off
23 17-20 leaves separated; 50% caps off (= flowering)
25 80% caps off
26 Cap-fall complete
27 Setting; young berries enlarging (>2 mmdiam.), bunch at right angles to stem
29 Berries pepper-corn size (4 mm diam.);bunches tending downwards
31 Berries pea-size (7 mm diam.)
32 Beginning of bunch closure, berries touching(if bunches are tight)
33 Berries still hard and green
34 Berries begin to soften;Sugar starts increasing
35 Berries begin to colour and enlarge
36 Berries with intermediate sugar values
37 Berries not quite ripe
38 Berries harvest-ripe
39 Berries over-ripe
41 After harvest; cane maturation complete
43 Beginning of leaf fall
47 End of leaf fall
4 Budburst
Inflorescence clear,5 leaves separated
50% caps off
Young berries growingBunch at right angles to stem
Bunches hanging down
Berry softening continuesBerry colouring begins
Berries ripe
12 Shoots 10 cm
19 Flowering begins
23 Flowering
27 Setting
31 Berries pea-size
35 Veraison
38 Harvest
Sh
oot
and
inflo
rescence
develo
pm
ent
Flo
werin
gB
erryfo
rmatio
nB
erryrip
enin
gSen
escence
MAJOR STAGES ALL STAGESE-L number
Viti 1 Chapter 07 Phenology 27/9/05 10:18 AM Page 153
5 New Zealand Winegrowers I nzwine.com
3
Grapevines are almost entirely resistant to freezing during frosts of less than -3°C (bud tissuetemperature) by virtue of their ability to supercool (Fuller and Telli, 1999). Dissolved solutesmay lower the freezing point of liquid in bud tissues by 1-2°C through freezing pointdepression. This means that water may be retained in a liquid state at temperatures less than0°C (= supercooling). When water freezes within plant cells it ruptures cell membranes,killing the cells and tissues. Ice nucleation normally occurs when the bud temperature falls to-3°C to -3.5°C. If frosts occur at an early stage of development (up to and including DS02:buds swollen but not yet at cotton bud stage, see Figure 2) then injury is slight and non-lethal.Whereas, if frosts occur when buds are at DS03 or later (DS03: emergence of brown downamong the scales, i.e. cotton buds) then they can be almost completely killed. The freezing ofbuds can be correlated with their water content. During the early stages of development(DS0, DS01, DS02, DS03) the bud water content rapidly increases from approximately 40%to 80% (Figure 2). During this transition, buds gradually lose the ability to supercool and therisk of frost damage increases.
Figure 2. Changes in water content of grapevine buds during initialdevelopment stages (DS), (adapted from Fuller and Telli,1999).
Spontaneous ice nucleation always occurs internally within the canes, before it occurs withinthe buds, during early stages of bud growth. The rate of ice spread in canes is comparable tothe rate of spread in pure supercooled water (0.47 cm s-1), suggesting that the ice is travellingin the bulk water contained within xylem vessels in the canes (Hamed et al., 2000). The lackof a fully functional xylem system between canes and buds, that exists during bud burst, isproposed to act as a barrier to the spread of ice from the canes into bud tissues during thistime.
This report discusses a series of trials that were undertaken on commercial vineyards inHawke’s Bay following the radiation frosts that occurred during spring in 2002. Theobjectives of these trials were to assess productivity, fruit development and fruit qualitycharacteristics of Chardonnay and Merlot vines that were either partially or completelydamaged during spring frosts, compared with vines that suffered no frost damage on the samevineyard, and to evaluate the effects of different post-frost management strategies on yield,fruit development and fruit quality.
Developmental stage
Bud water content (%) 40 55 78 80 85 85
DEGREE OF DAMAGE
The more advanced the phenological stage, the
more susceptible the grapevine is to frost. The
extent of damage will depend on the stage of vine
development and the severity of the frost. Damage
to plant tissue is caused by ice crystal growth – ice
crystals puncture plant cell membranes, causing
cell death. If enough cells die, the bud, leaf or flower
will be destroyed. As Figure 2.1 illustrates, the water
content of grapevine buds increases rapidly during
initial development stages. During this transition, the
risk of frost damage increases.
Figure 2.1. CHANGES IN WATER CONTENT OF GRAPEVINE BUDS DURING INITIAL DEVELOPMENT STAGES
CRITICAL TEMPERATUREThis refers to the lowest temperature plant tissue
(such as a bud) can endure for 30 minutes or less
without injury. It is the temperature within the plant
rather than atmospheric temperature that is critical.
It provides crucial information when determining
when to activate frost protection systems. Table 2.1
shows critical tissue temperatures observed in Pinot
Noir.
• Dormant tissue may be able to withstand
temperatures as low as -15 °C.
• Developing buds, depending on the stage of
development, may withstand temperatures from
-9.5 °C to -3.0 °C.
• Young tissues (new leaves and flowers) are
susceptible to temperatures only slightly
below 0 °C.
In the vineyard, the presence of surface moisture
increases the susceptibility to frost injury
(see Table 2.2).
Table 2.1. CRITICAL TISSUE TEMPERATURE (°C ) AT WHICH DAMAGE IS OBSERVED IN PINOT NOIR
Stage of development50% tissue death No damage
Dormant enlarged -14.0
Green swollen -3.4
Shoot burst -2.2 -1.0
First leaf -2.0 -1.0
Second leaf -1.7 -1.0
Fourth leaf -1.2 -0.6
Source: Trought, 2003 (from Gardea 1987)
Table 2.2. ROLE OF SURFACE MOISTURE
Stage of development
Modified E-L scale
Influence of surface moisture
WET DRY
Scale crack 2 -5.5 -9.5
First swell -4.5 -8.5
Full swell 3 -3.5 -7.0
Burst 4 -3.0 -6.0
Source: Martin, 2013
Source: McCartney, Chatterton and Good, 2003
6 New Zealand Winegrowers I nzwine.com
DEFINING SEVERITY OF THE FROSTA simple way of quantifying the intensity of a
frost event is to accumulate the (screened) air
temperatures below zero on an hourly basis
(Figure 2.2).
For example, if during a three-hour frost the
temperatures recorded each hour were -1 °C, -2 °C
and -2 °C respectively, the accumulated degree-
hours would be -5 °C. Figure 2.2 provides an
estimation of frost damage (frost intensity is to
screened air temperature).
ENVIRONMENTAL CONDITIONSFrost risk may be reduced if it is windy, because air
movement reduces the insulation effect of still air,
helping to raise plant tissue temperature.
Under still conditions, the internal bud temperature
may end up 2 °C to 3 °C lower than the air
temperature. Wind speeds of 3 to 4 kilometres
per hour (kph) will minimise this effect, with air
movement around the bud bringing bud and air
temperatures much closer together.
Frost risk is lowered when there is free water in the
soil during a radiative frost. Heat is released from
this water into the air, reducing the affect of freezing
temperatures.
Free water on buds, however, will increase
susceptibility to frost damage.
No or light damage
Moderate damage
Severe damage
-15
-10
-5
Fros
t Int
ensi
tySu
m o
f deg
ree
hour
s bel
ow ze
ro (C
°)
1 5 10 15 25
Modified Eichhorn-Lorenz (E-L) Growth Stage
20Budburst FloweringInflorescence clear
Frost Severity Estimation ChartFigure 2.2. FROST SEVERITY ESTIMATION CHART
MORE RESOURCES ON NZWINE.COM:
Damage processes and symptoms – New Zealand
Winegrowers Fact Sheet
Post-frost event – preparing for the next year
after a frost, Damian Martin (Grape Days 2013:
Presentation notes and video)
References
• Trought MCT, Howell GS and Cherry N. 1999.
Practical Considerations for Reducing Frost
Damage in Vineyards. Report to New Zealand
Winegrowers.
• McCartney S, Chatterton D and Good M.
Dealing with frost: describing vine response
to frost damage and the impact of post-frost
management on vine performance, October
2003, Report to New Zealand Winegrowers.
• Trought MCT, 2003. New Zealand Winegrowers
Romeo Bragato Frost Workshop, Wellington.
Source: Martin, 2013
7 New Zealand Winegrowers I nzwine.com
III – FROST FORECASTING
No frost protection method will protect against
all types and severities of frost. Knowing the
conditions that occur most frequently in your
vineyard is the first step in determining which
system to use.
• Compare the frosts that are forecast to the
temperatures at your vineyard.
• Understand the importance of your canopy/
cordon height and the impact this has on
temperature.
PLANNINGKnowing what the night’s minimum temperature is
likely to be – and how it might change – is essential
to frost management.
Vineyard managers should be actively involved in
frost forecasting and frost protection. Forecasting is
not something that can be left to weather stations
and frost alarms alone. Data collected from on-site
weather stations can be used to determine:
• What types of frost occur.
• What type of frost protection will be effective.
• Where to apply frost protection.
Weather station data can also be used during
frost events to determine when and for how long
protection is required.
Creating a frost protection plan is a good first step
in determining frost protection requirements. A
site map will outline areas with varying conditions
(such as elevations, temperature extremes, timing
of budburst) and historical frost protection methods
used, if any. Maps should be based on weather data,
topographic information, personal observations
over time and vine management records.
FORECAST SOURCESON-SITE FORECASTING
While off-site regional forecasts provide valuable
information, including historical data, they are
seldom specific to your vineyard block(s).
Minimum temperatures can differ widely within a
region. Factors that affect temperature, humidity,
wind speed and inversion strength at your site may
result in several mesoclimates, with differing risks in
terms of the potential for frost damage.
Many vineyard managers supplement off-site
forecasting with on-site weather stations.
Figure 3.1. On-site weather stations often include temperature and humidity
sensors, as well as reporting and alarm systems.
In recent years, technological advances have
brought sophisticated weather stations within the
financial reach of many growers. While the makeup
of these weather stations varies between services,
they commonly have:
• A solar-powered wireless base system with a
range of sensors including temperature and
humidity sensors.
• A data reporting system (often to a web page via
a weather database and server).
• Alarm systems that send text, voice or email
messages when conditions fall outside specified
8 New Zealand Winegrowers I nzwine.com
thresholds (which can be configured to each
location). Alarm systems are now available with
multiple sensors that can be placed in a variety of
locations throughout the vineyard.
Depending on the model, these units can also:
• Activate frost fans or sprinkler systems (auto
start).
• Monitor the performance of frost fans or sprinkler
systems (for example, fuel level and engine rpm
of frost fan and pump performance of sprinkler
systems).
• Activate strobe lighting in specific areas to direct
helicopters being used for frost protection.
OFF-SITE FORECASTING
Off-site weather forecasting tools and services
are offered by the NZ Meteorological Service
(MetService) and NIWA (National Institute of
Weather and Atmospheric Research). You can learn
more about the online tools available by visiting the
websites below:
• Rural regional forecasting at MetService
http://metservice.com/national/home
• Web-based weather forecasting at NIWA
http://www.niwa.co.nz/online-services/niwa-
forecast
There are also private companies that provide frost
forecasting services, either as part of a customised
product or as a standalone service.
CALIBRATING ON-SITE CONDITIONSIf you are not using on-site weather stations,
regional frost forecasts form the start of your frost
forecasting process.
Your first step – which only needs to be done once
unless you make major changes to your site – will be
to modify the expected minimum temperature from
the regional forecast to the local conditions of your
own vineyard by monitoring on-site and over time
with some form of temperature measurement.
CALCULATING RISKCalculating frost risk will help to determine when to
activate frost protection and several approaches are
available.
DEW POINT ESTIMATES
The dew point is the temperature at which the
relative humidity reaches 100% as the air cools. At
this point, water vapour in the air condenses into
fog or dew, which gives off heat, slowing the drop in
temperature.
The dew point temperature measured at 3 p.m.
provides a useful estimate of the upcoming
minimum temperature under clear and calm
conditions. The dew point can be estimated by
measuring relative humidity and air (dry bulb)
temperature, or air and wet bulb temperature.
Using these measurements, the dew point
temperature can be read from prepared tables
(such as those provided on MetService at http://
about.metservice.com/about-metservice/
learning-centre/frost/) or accessed from freely
available online calculators (such as http://www.
dpcalc.org/).
For example, the MetService table indicates that
a 3 p.m. temperature of 11 °C and a 50% Relative
Humidity results in a dew point of 1 °C. Deducting
4 degrees from an estimated overnight low of 1 °C
gives an estimated ground minimum temperature of
-3 °C. In other words, a moderate frost that could be
damaging in spring.
While the 3 p.m. dew point temperature provides an
indication of the expected night-time low, the actual
temperature may be lower, particularly if the night is
calm and clear and is longer than 12 hours.
OVERNIGHT MINIMUM GRASS TEMPERATURE
An alternative method is to predict the overnight
grass minimum temperature using predictive
models such as those provided by MetService and
NIWA (mentioned earlier).
9 New Zealand Winegrowers I nzwine.com
EXCEL-BASED PROGRAMMES
More precise local forecasts can be made using a
pair of freely available Excel-based programmes
developed by meteorologists at the University of
California and Lisbon Technical University:
o FFST_M uses historical records of air and dew
point temperatures to forecast the minimum
temperature from inputs of air temperature alone
or with dew point temperature measured two
hours after sunset.
o FTrend_M uses forecast minimum air temperature
and dew point temperature to determine the air,
wet bulb and dew point temperature trends during
a radiation frost night, giving you an indication of if
and, as important, when during the night you need
to activate your active frost protection (such as a
sprinkler system or frost fans).
MORE RESOURCES ON NZWINE.COM:
Forecasting – New Zealand Winegrowers Fact Sheet
References
• Trought MCT, Howell GS and Cherry N. 1999. Practical Considerations for Reducing Frost Damage in
Vineyards. Report to New Zealand Winegrowers.
• Snyder RL and Paulo de Melo-Abreu J. 2005. Frost Protection: fundamentals, practice, and economics
(Vol. 1). Food and Agriculture Organization of the United Nations, Rome.
http://www.fao.org/doCrep/008/y7223e/y7223e00.HTM
10 New Zealand Winegrowers I nzwine.com
IV – FROST CONTROL METHODS
Given the financial implications of failures in frost
protection, it is important to take qualified advice
before relying upon any method for protecting your
crop against frost.
Before investing in a frost protection system,
growers should also review the New Zealand
Winegrowers Code of Practice (at the end of this
booklet), which discusses related issues such as
district plan requirements.
Table 4.1
FROST CONTROL METHODS
Passive ActiveGroundcover / soil management
Air mixing – frost fans or helicopters
Delayed pruning Sprinkler systems
Trellis height Heaters
PASSIVE METHODS
Available to every grower, passive control methods
are effective and often help prevent frost damage in
a vineyard.
GROUNDCOVER / SOIL MANAGEMENT
Prepare the vineyard floor:
• Ensure inter-row grass or cover crops are closely
mown (generally to less than 5 cm), and soils are
moist and firm.
• Keep on top of weed growth.
Loosely cultivated soil or deep inter-row herbage
provide an insulating layer on the soil surface that
will restrict heat absorption during the day and
restrict the ground’s ability to re-radiate heat out
during the night.
An absolute focus on keeping on top of weed
growth and achieving a short sward can secure
up to a 1 oC elevation in canopy temperatures on a
frost-prone site.
Removing all ground cover (compacted bare earth)
enhances frost protection further by completely
removing the insulating layer. To increase the
temperature by about 0.5 oC, the soil surface
will have to be firm. Ground preparation must be
done well before a predicted frost – ideally, before
budburst.
Ice-nucleating bacteria are plant pathogens that
cause freezing injury. The concentration of ice-
nucleating bacteria on grass and ground covers is
typically high.
DELAYED PRUNING
• Employ late spur pruning to delay budburst,
reducing the vulnerability of developing shoots to
frosts.
• Leave additional canes post-pruning, which may
or may not be used in the event of a frost. This
will allow additional shoot selection should a frost
occur, optimising vine yield.
TRELLIS HEIGHT
• Raise fruiting wires. For every 100 mm the wire is
above the ground the temperature will increase by
approximately 0.2 oC.
Figure 4.1: Canopy management can be used to fight frost. For every 100 mm
the wire is above the ground, the temperature will increase by approximately 0.2 oc.
11 New Zealand Winegrowers I nzwine.com
ACTIVE METHODS
Active frost protection measures are implemented
just before and during frost events to mitigate the
risk of damage. Active methods rely on a range of
technologies, and include:
• Diesel return stack heaters.
• Air mixing by helicopters and frost fans.
• Application of water through sprinkler systems.
No system, however, is able to guarantee crop
protection against frost damage.
HEATERS
Diesel return stack heaters provide frost protection
by directly heating the air in the vineyard, which, in
turn, provides some radiant heating of the vines.
Quantity is critical: approximately 150 to 200
heaters per hectare may be required in colder
regions to achieve a level of frost protection.
Positioning of heaters is also critical. If placed
downwind in the vineyard, the heating benefits may
go to your neighbour’s block rather than your own.
Pros:
• Are proven to protect against typical radiation
frosts.
• Provide some protection under advective frost
conditions.
• Flexibility of placement enables targeting of frost
pockets within the vineyard.
Cons:
• Very high operational costs.
• Labour intensive.
• Protection is based on combustion, increasing
carbon footprint.
Figure 4.2
Diesel return stack heaters provide frost protection by directly heating the air in the
vineyard, which, in turn, provides some radiant heating of the vines.
FROST DAMS
Because cold air drains downhill much like water,
vineyard managers have used vegetation, buildings
and other structures to protect against frost. This
can be done by erecting frost dams upwind to
block the flow of cold air or by removing shelter
and/or providing gaps downwind to drain cold
air away from vines. Berm walls, fences and other
structures have been used to redirect cold air and
provide a measure of frost protection.
Foliar applications such as urea and copper
sulphate may provide limited frost protection, but
they must be applied before frost occurs.
MORE RESOURCES ON NZWINE.COM:
Modifying sites to reduce frost risk – New Zealand
Winegrowers Fact Sheet
Choosing sites with low frost risk – New Zealand
Winegrowers Fact Sheet
References
• Trought MCT, Howell GS and Cherry N. 1999.
Practical Considerations for Reducing Frost
Damage in Vineyards. Report to New Zealand
Winegrowers.
12 New Zealand Winegrowers I nzwine.com
FROST FANS
Two- and four-blade machines remain the most
popular form of fixed protection in NZ vineyards,
partly because of cost (they cost roughly half
as much per hectare as a water-based sprinkler
system). Frost fans (also known as wind machines)
are also easier to maintain and service and are
relatively straightforward to manage during a frost
event. They are not suitable for every site, however,
particularly where inversion conditions are weak.
Depending on the make and model, one frost fan
can protect 4-plus hectares under ideal conditions.
Air mixing technologies do not add significant
amounts of heat. They simply redistribute heat
by mixing the warmer upper layer with the cooler
ground layer, thereby raising the temperature at the
vine level during a radiation frost.
Bringing warm air from above the inversion down
to the ground typically increases temperatures by
about 1 oC to 2 oC, but there must be an inversion
present. Air mixing does not work for advective
frosts.
Placement is critical: the upper gearbox rotation
time should be close to or less than the industry
standard of 6 minutes and 40 seconds. Individual
manufacturers’ standards may vary. Air is drawn
down from heights of 20 m+ by blades slightly
angled towards the ground and mixed with colder
air near the surface.
Information on the strength of an inversion layer
at a specific site should be determined before any
purchase or installation of a fixed frost protection
system.
Helicopters and frost fans protect less area
when inversion conditions are weak or surface
temperatures are very cold.
Figure 4.3 Two- and four-blade frost fans remain the most popular form of fixed
protection in NZ vineyards.
Figure 4.4 HOW DO FROST FANS WORK?Air mixing technologies do not add significant amounts of heat. They simply redistribute heat by mixing the warmer upper layer with the cooler ground layer, thereby raising the temperature at the vine level during a radiation frost.
13 New Zealand Winegrowers I nzwine.com
Activation
Fans are usually started while the temperature
measured at 1.5 m height is still above the critical
damage temperature – typically, fans are set to
auto start at 0.5 oC, but growers can adjust them to
vineyard conditions (usually, from 0.3 oC to 1.5 oC).
In areas where wind speeds during frost can be
a problem, the frost fan should be fitted with an
auto anemometer. This will shut the fan down when
wind rises above a set maximum speed and start it
again when the wind returns to below-critical levels.
Run your fans according to the manufacturer’s
specifications.
Pros:
• Are proven to protect against typical radiation
frosts.
• After installation, are always available and can be
set to start automatically (auto start).
• Have relatively low running and maintenance
costs (between 19 to 34 litres of diesel per hour
per machine, depending on the make and model)
and a low energy cost compared to heaters.
Cons:
• Are not effective under advection frost conditions.
• Have relatively high capital cost (approximately
$50,000 to $60,000 per machine – which
converts to somewhere between $7,500 to
$12,500 per hectare protected, depending on the
make and model).
• Some machines emit noise that can be a problem
near dwellings and may limit installation consents.
• Not recommended when wind speeds exceed 7 kph
(see the Appendix: New Zealand Winegrowers
Code of Practice 2014).
Frost fans must be monitored during the night. They
must be switched off if wind gets up too much or it
starts to get foggy or snows. Frost fans can fail due
to blade-icing (observed in Central Otago).
The auto start feature on all frost fans can also fail,
either initially or once it has run.
HELICOPTERS
Like frost fans, helicopters redistribute heat by
mixing the warmer upper layer with the cooler
ground layer, thereby raising the temperature at the
vine level during a radiation frost.
Bringing warm air from above the inversion down
to the ground typically increases temperatures by
about 1 oC to 2 oC, but there must be an inversion
present. Air mixing does not work for advective
frosts.
Figure 4.5 Like frost fans, helicopters redistribute heat by mixing the warmer
upper layer with the cooler ground layer, thereby raising the temperature at the vine
level during a radiation frost.
Estimates vary, but the coverage area protected by
one helicopter can range from between 10 to 40
hectares. The area protected will depend on the size
and weight of the helicopter, the power and thrust
from the blades, and on weather conditions. As the
temperature falls, helicopters protect significantly
less area.
Ideally, helicopters should have a return period of
no more than five minutes to the same point – and
certainly no more than 30 minutes (this determines
the number of helicopters required). Flight paths
should be in a zigzag pattern into the prevailing
katabatic drift and flight height is usually about 15
metres above ground.
14 New Zealand Winegrowers I nzwine.com
Use coloured frost lights as a guide for pilots.
As the temperature drops, colours will change,
signalling areas requiring attention.
Figure 4.6: Helicopter operations fighting frost in a New Zealand vineyard.
Ground temperature needs to be monitored as the
helicopter passes above to ensure that temperature
rises rather than falls. If the inversion layer weakens
too much (typically just before sunrise, when it is
coldest) air mixing can do more harm than good.
Having a temperature sensor on the helicopter
is also helpful. Maintain communication with the
helicopter pilot at all times.
Pros:
• Are proven to protect against typical radiation
frosts.
• May provide some protection even under very
weak inversion conditions.
• Need only pay for when called.
• No need for additional infrastructure in the
vineyard.
Cons:
• Are not effective under advection frost conditions.
• Have to be booked in advance of a frost, and
standby costs apply even if not used.
• Availability during frost season not always
guaranteed.
• Relatively high running costs and noise emissions.
• Almost never available for the unpredicted frost.
WATER APPLICATIONS
Sprinkler irrigation for frost protection works
because water releases heat when it changes
from a liquid to a solid (ice). In cold conditions,
the clear ice that forms on the crop as a result of
sprinkler applications serves as a good conductor
of heat. However, ice does not act as an insulating
layer to prevent frost damage. Rather, it facilitates
freezing of crop tissues unless a film of continuously
freezing water is maintained on the surface of the
ice, releasing sufficient latent heat to maintain
temperature just below 0 oC.
Today there are a range of sprinkler systems used
in frost protection. Vineyards in New Zealand
commonly use one or more of the following:
1. Traditional, full cover (overhead impact) sprinklers
that are fixed in place and completely wet the
plants and soil, providing 100% coverage (typically
manufactured in brass).
2. Targeted micro or mini sprinklers, which apply
water only to the vines, rather than the entire
vineyard (typically manufactured in plastic).
3. Hybrid full cover impact sprinklers (metal and
plastic materials, depending on componentry).
Note: Full cover overhead sprinklers offer the
only reliable protection under both radiation and
advection frost conditions, provided a sufficient
amount of water is applied. They are not suitable
for every soil type, however, and may have high
water storage requirements.
15 New Zealand Winegrowers I nzwine.com
Full cover sprinklers
These systems will work in advective or mixed
events where frost fans or helicopters won’t.
Dew point is critical. Vineyard managers need to
monitor the dew point and turn on sprinklers before
the damage point is reached for the current growth
stage. This is likely to be different at both ends
of the season – in spring, it’s typically -0.5 oC but
can be as low as -2 oC during autumn. The water
rate should increase as temperature decreases. Ice
formation should remain clear. If ice turns opaque,
there is insufficient water application and damage to
sensitive plant tissue may occur.
Figure 4.7: Overhead sprinkers will work in advective or mixed events where
frost fans or helicopters won’t.
Figure 4.8: Ice formation should remain clear. If ice turns opaque, there is
insufficient water application and damage to sensitive plant tissue may occur.
The accompanying tables were established by
bio-meteorologist Richard Snyder (University
of California) to indicate when to start and stop
sprinklers for frost protection based on temperature
and humidity (that is, the critical damage
temperature for the current growth stage).
You must run the sprinklers until all the ice has
melted from the protected area of the vineyard –
otherwise tissue damage will occur.
Note that you will need a site-specific means of
measuring dew point if you are using water as your
means of frost protection.
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Select a wet bulb temperature that is above the critical damage temperature for the pertinent growth stage and locate the appropriate column. Then choose the row with the correct dewpoint temperature and read the corresponding air temperature from the table to turn your sprinklers on or off. This table assumes a barometric pressure of 1013 millibars (101.3 kPa).
Source: Snyder, 2005
Table 4.3 DEW-POINT TEMPERATURE (OC) FOR A RANGE OF AIR TEMPERATURE AND RELATIVE HUMIDITY
Relative humidity Temperature (oC)
% 0.0 2.0 4.0 6.0 8.0 10.0
100 0.0 2.0 4.0 6.0 8.0 10.0
90 -1.4 0.5 2.5 4.5 6.5 8.4
80 -3.0 -1.1 0.9 2.8 4.8 6.7
70 -4.8 -2.9 -1.0 0.9 2.9 4.8
60 -6.8 -4.9 -3.1 -1.2 0.7 2.6
50 -9.2 -7.3 -5.5 -3.6 -1.8 0.1
40 -12.0 -10.2 -8.4 -6.6 -4.8 -3.0
30 -15.5 -13.7 -12.0 -10.2 -8.5 -6.8
Select a relative humidity in the left column and an air temperature from the top row. Then find the corresponding dew point in the table.
Source: Snyder
Table 4.2: MINIMUM TURN-ON AND TURN-OFF AIR TEMPERATURES (OC) FOR SPRINKLER FROST PROTECTION
Dew-point temperature Wet bulb temperature (0 oC)
0 oC -5.0 -4.0 -3.0 -2.0 -1.0 0.0 0.0 0.0
-1.0 -1.0 0.7
-2.0 -2.0 -0.4 1.3
-3.0 -3.0 -1.4 0.2 1.9
-4.0 -4.0 -2.5 -0.9 0.8 2.4
-5.0 -5.0 -3.5 -1.9 -0.4 1.3 2.9
-6.0 -4.5 -3.0 -1.5 0.1 1.8 3.4
-7.0 -4.1 -2.6 -1.0 0.6 2.2 3.9
-8.0 -3.6 -2.1 -0.6 1.0 2.6 4.3
-9.0 -3.3 -1.7 -0.2 1.4 3.0 4.7
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Water volume requirements
For effective frost control using full cover overhead
sprinkler irrigation, growers must apply water at a
rate:
• High enough to release sufficient latent heat that
temperatures are prevented from dropping much
below 0 oC.
• Low enough to avoid unacceptable levels of
waterlogging of the soil (see the New Zealand
Winegrowers factsheet on soil water status).
A useful rule of thumb is that each millimetre of
water applied per hour can be expected to maintain
plant temperatures one degree above the frost
temperature.
For example, an application rate of 4 mm/hr can
hold plant temperatures at -0.5 oC to 0 oC in a
-4 oC frost. However, higher sprinkling rates will be
required to ensure protection in situations where
sprinkler cover on the crop is not uniform and/or in
wind conditions where evaporative cooling becomes
a factor. In such conditions, sprinkling rates of 1.5
mm/hr or more may be required to achieve a 1 oC
rise in plant temperature.
You can easily check that the correct temperature is
being maintained by looking at the ice being formed:
• When sprinkling rates have been acceptably high
and freezing is continuous, the crop is covered in
icicles of clear ice (as shown in Figure 4.9).
• When sprinkling rates have been insufficient for
continuous freezing, icicles tend to be absent
and trapped air in the ice makes it white; tissue
damage is likely to have occurred.
The total volumes of water required for sprinkler-
based frost protection are greater than those
needed for irrigation (see Table 4.4). As the whole
protected area needs to be wetted at the same time,
the overall pumping capacities required far exceed
those for systems used solely for irrigation.
Typical weather patterns in New Zealand can
produce a series of potentially damaging frosts
over several days, so the necessary amount of
water needs to be available for several nights
in succession. Planning for water storage and
pumping capacity sufficient to provide protection
under realistic worst-case scenarios for frost risk is
an important part of the design of sprinkler frost
irrigation systems. Plan for three consecutive nights
of frost protection, with refilling of the reservoir
beginning as soon as frost protection starts.
The water rate required will depend on the sprinkler
system’s rotation rate plus the wind speed and the
dew point temperature. Evaporation increases with
wind speed and decreasing dew point temperatures.
The goal is to re-wet the vines frequently so that the
interval when tissue must withstand temperatures
below the critical damage threshold is short (no
longer than 60 seconds).
Correct engineering design is essential to match
application rates to frost risk. A report prepared
for Hawke’s Bay Winegrowers, Improving Sprinkler
Frost Control In New Zealand Vineyards provides
comprehensive coverage on this topic (see
‘References’ at the end of this section for the
complete notation).
Figure 4.9: Ice-encased leaves and flower following overhead sprinkler frost
protection – note the clear ice which is indicative of near continuous wetting.
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Tissue Temperature
Wind Speed ( Km h-1 )
0-1.5 3.0-6.5 8-13 15-22 29-32 48
-2 - - - - - -
-3 0.25 0.25 0.36 0.50 1.00 1.50
-4 0.25 0.40 0.75 1.00 2.00 4.00
-5 0.30 0.60 1.25 1.50 3.00 4.50
-6 0.35 0.70 1.40 1.80 3.65 5.25
-7 0.40 0.75 1.50 2.00 4.00 6.00
-8 0.50 1.00 1.75 2.50 5.00 7.50
-9 0.65 1.75 2.25 3.30 6.60 10.00
Source: Trought, 1999 (modified after Gerber, 1970)
Pros:
• The only frost protection method that reliably
protects under both radiation and advection frost
conditions is the full cover sprinkler.
• Provided sufficient water is available, water
pumping costs are lower than the energy costs of
heaters for frost protection.
• Application rates can be refined to reduce costs
and water.
Cons:
• Require large volumes of water that necessitate:
o Appropriate water storage (dams/reservoirs).
o Consent for using the water.
• High water use can waterlog soils, potentially
creating problems with:
o Soil structure.
o Soil and plant health.
o Access for machinery.
• Relatively high installation costs (these will
vary depending on the water storage capacity
required) and high maintenance costs.
Under canopy micro or mini sprinklers
Micro or mini sprinklers use less water than full
cover overhead sprinklers. They may provide a
useful, but limited, temperature rise that can help
protect against damage from light frosts or increase
the efficacy of frost fan protection.
Pros:
• Little additional capital costs are incurred because
existing irrigation systems can be used.
• Low running costs.
Cons:
• Provide limited protection that tends to be useful
only in radiation frosts.
• Usually made of plastic and typically require more
maintenance than metal full cover sprinklers.
Table 4.4 SPRINKLING RATE (MM H-1) NECESSARY FOR COLD PROTECTION
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CHECKLIST BEFORE FROST FIGHTING
• Make sure your frost alarm or weather station sensors are working and information is going to the correct
staff.
• Know how many litres of fuel per hour your machine uses and ensure that there is enough diesel for the
following night by dipping the tanks and prioritising refills at the end of the frost fighting session.
• Frost fans should also be checked prior to running – remove bird nests, which may catch fire and damage
the engine.
• Ensure that frost fan batteries are fully charged.
• Frost fans should also be run monthly to ensure oils and water circulate and should be calibrated by ice
twice a year to ensure preparedness for spring and autumn frosts.
• Subscribe to an area-specific forecast.
MORE RESOURCES ON NZWINE.COM:
Heaters for active frost protection – New Zealand Winegrowers Fact Sheet
Wind machines and helicopters for active frost protection – New Zealand Winegrowers Fact Sheet
Overhead sprinkler irrigation for active frost protection – New Zealand Winegrowers Fact Sheet
Soil water status – New Zealand Winegrowers Fact Sheet
Under-canopy sprinkler irrigation for active frost protection – New Zealand Winegrowers Fact Sheet
REFERENCES
• Yule I, Eastwood CR, Murray RI, Lawrence HG, Johnson G, Impact of topography on frost protection
machine performance, Report to New Zealand Winegrowers, 2003.
• Woodhead I, Richards S, Hayward A. Improving Sprinkler Frost Protection in New Zealand Vineyards,
Summary Report from 2004-2007 Data. Report to Hawke’s Bay Winegrowers.
• Ireland W. 2005. Frost and Crops: Frost prediction and plant protection. ISBN 0-473-10108-4.
• Snyder, R.L. and de Melo-Abreu, J.P. 2005. Frost Protection: fundamentals, practice, and economics
Volume 1. FAO. ISBN: 92-5-105328-6 http://www.fao.org/doCrep/008/y7223e/y7223e00.htm#Contents
20 New Zealand Winegrowers I nzwine.com
V – REDUCING FROST DAMAGE
Frost damage is most likely to occur in spring,
during early growth stages.
Damage may not be immediately apparent.
Consider waiting before taking any action.
Symptoms of frost damage may take one or more
weeks to appear and will indicate which remedial
actions are appropriate.
The goal is to:
• Maximise crop for the current season if possible.
• Ensure the vine is in the best possible position for
the following season, so that crop and vine health
are not compromised.
POST-FROST
A frost event has occurred. The question now is,
‘What should I do next?’
If frost protection has been unsuccessful, damage
in the spring can reduce the current crop as well as
reduce the crop in following seasons.
ASSESSMENT OF DAMAGE
Frost damage may not be immediately apparent.
Consider waiting until symptoms of frost damage
appear. There is a trade-off, however, between
waiting to see the outcome and a quick response to
minimise frost damage.
• Leaf damage is usually evident. Loss of
chlorophyll, transparent sections on leaves or
bubbling on the leaf surface may be observed.
• Young succulent shoots will wilt once the frost
thaws, but older hardened shoots will take longer
to show symptoms.
• Frosting of inflorescences may not be
immediately apparent. Later, they begin to dry out
and individual flowers start to fall off, particularly
when handled.
Figure 5.1 Leaf damage is usually evident. Loss of chlorophyll, transparent
sections on leaves or bubbling on the leaf surface may be observed.
FROST DAMAGE IN SPRING
DETERMINE OBJECTIVES FOR THE REMAINDER
OF THE SEASON
The chosen approach will depend on a range of
factors:
• The severity of the frost.
• The phenological stage when the frost occurs.
• The rapidity with which vines are growing and
how much water they have in them.
• The region and length of growing season available
after the frost.
• The pruning system.
• The grape variety.
• The targeted wine style (which may change
following the frost).
Assess cropping potential – the impact of variety
and training system need to be factored into your
predictions. Most grape varieties have fruitful
secondary buds that can produce a smaller crop
(in the case of some varieties, much smaller).
On some training systems, fruitful shoots may
arise from bud positions other than those on
canes retained and counted at pruning. Check
whether there will be enough growing season to
21 New Zealand Winegrowers I nzwine.com
allow any new bunches to fully ripen. Bear in mind
that a reduced crop might mature faster than an
undamaged full crop.
Strategies for maximising crop in the current year
will differ from strategies to produce good canes for
pruning in winter.
The following checklists for managing frosts of
different severity at different points in the growing
season were prepared by Damian Martin, Science
Group Leader Viticulture & Oenology at Plant &
Food Research, and first presented to the wine
industry at New Zealand Winegrowers’ Grape Days
events in 2013.
OPTIONS FOR MANAGING FROST DAMAGE
LIGHT EARLY-SEASON FROST DAMAGE
• Many primary buds will survive and crop normally.
• The vine’s reserves are likely to still be abundant.
• Not usually necessary to promote shoot growth of
replacement canes.
• Fruit that forms on secondary buds are
comparable to second set.
• Manage according to the variety and targeted
wine style.
• Premium red wines – green-thin fruit at veraison.
• White and sparkling-based wines – input is
probably not warranted.
SEVERE EARLY-SEASON FROST
• Virtually all primary buds will be destroyed.
• Crop will only come from unburst primary buds
and secondary/tertiary buds.
• Fertility of secondary and tertiary buds is modest;
they are never as fruitful as first buds and
fruitfulness will vary by variety. A good rule of
thumb is to allow only one small bunch for every
two shoots.
• The spring development of new shoots will be 3-4
weeks behind the pre-frost growth stage.
• Still enough time for the replacement canes to
develop fully and harden.
• Crop may also still ripen and be relatively uniform.
• Pruning input not necessary.
Following an early frost, applications of nitrogen
fertiliser and water can help regrowth and restore
the vine’s reserves.
MODERATE MID- TO LATE-SEASON FROSTS
• Well-developed shoots only partially damaged.
• Lateral growth is strongly stimulated.
• The spring development of new shoots will be 4-8
weeks behind the pre-frost growth stage.
• Priority is to ensure that there are good quality
replacement canes or spurs available for winter
pruning.
• Replacement canes with multiple lateral branching
and poorly matured wood (laterals harden off less
well than primary shoots).
• Current season’s crop becomes secondary
priority.
• Pruning input is recommended (see Table 5.1). The
focus is to ensure replacement wood.
SEVERE LATE-SEASON FROSTS
• Well-developed shoots only partially damaged.
• Lateral growth is strongly stimulated.
• Vines’ reserves are greatly depleted and regrowth
can be very late and/or slow.
• Even more important to direct the remaining
reserves into the replacement canes.
• Current season’s crop should be forgotten
altogether.
• Major pruning input is recommended
(see Table 5.1).
22 New Zealand Winegrowers I nzwine.com
Table 5.1: PRUNING AFTER A FROST
Early Spring Mid Spring Late Spring
LIGHT DAMAGE No pruning N fertiliser and water still recommended.
No pruning N fertiliser and water still recommended.
No pruning N fertiliser and water still recommended.
MODERATE DAMAGE No pruning N fertiliser and water still recommended.
Prune the partly damaged green shoots back to 5 mm above the crown to stimulate growth of primary and tertiary buds. Breaking off shoots may damage replacement buds. Prune damaged shoots close to the head to ensure replacement canes are not dominated by laterals.
Prune the partly damaged green shoots back to 5 mm above the crown to stimulate growth of primary and tertiary buds. Breaking off shoots may damage replacement buds. Prune damaged shoots close to the head to ensure replacement canes are not dominated by laterals.
SEVERE DAMAGE No pruning N fertiliser and water still recommended.
Prune the partly damaged green shoots back to 5 mm above the crown to stimulate growth of primary and tertiary buds. Breaking off shoots may damage replacement buds. Prune all damaged shoots to promote secondary and tertiary buds and maximise cropping potential.
Prune canes midway along to reduce the bud load. Promote new shoot growth from the base of the cane and the head. Priority is replacement canes.
Source: Martin 2013
AUTUMN FROSTS
If fruit has been frozen, it should be harvested immediately. If only the leaves are killed, the sugar
concentration in the fruit will increase slowly through dehydration of the berry. Deciding when to harvest
must be weighed against the possibility of another frost and further reductions in fruit quality. Canes in
autumn should be sufficiently hardened to provide good canes and spurs for pruning in winter.
MORE RESOURCES ON NZWINE.COM:
Post-frost event – preparing for the next year after a frost, Damian Martin
(Grape Days 2013: Presentation notes and video)
Damage processes and symptoms – New Zealand Winegrowers Fact Sheet
References
• Trought MCT, Howell GS and Cherry N. 1999. Practical Considerations for Reducing Frost Damage in
Vineyards. Report to New Zealand Winegrowers.
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NEW ZEALAND WINEGROWERS
FROST FAN CODE OF PRACTICE 2014
Introduction
The New Zealand Winegrowers Frost Fan Code of Practice 2014 (the Code) represents a standard of good
practice in the safe operation of frost fans and takes the form of recommendations.
The intent of the Code is to provide guidance to the wine industry on the safe operation of frost fans:
a) when climatic conditions necessitate their use;
b) in accordance with local council rules; and
c) in a way that minimises risk and disturbance.
In accordance with section 3.1 of the Guidance on Planning for the Wine Industry (Ministry for the
Environment, Guidance Note, 2007), it is noted that any standards regulating the use of frost-protection
devices should recognise the infrequent occasions on which these devices may need to be used, typically
dependent on factors beyond a grower’s control.
It may be that, in some situations, strict compliance with all recommendations is impracticable. In such
circumstances, every endeavour should be made to observe the intent of the Code.
The good practice recommendations in this Code are voluntary and do not displace the obligation on
members to comply with the rules contained in the District or Unitary Plan of their relevant regional authority
or not to engage in any other conduct which may be in breach of the Resource Management Act 1991. In
particular, we draw attention to the relevant rules in each region on noise limits and location of frost fan from
boundary.
1 OPERATING ENVIRONMENT
1.1 Avoid operating a frost fan in the following conditions:
• fog;
• rain;
• when winds are at 7km/h or greater; or
• when there is no risk of frost (except for maintenance purposes, which should be conducted at a time
/ duration to minimise intrusion).
1.2 Where possible, shield the frost fan engine from vineyard sprays and/or irrigation sprinklers.
1.3 In order to prevent inadvertent start up the frost fan should be disarmed during periods when no frost
threat exists.
2 PRE-USE INSPECTION
2.1 Before operating the frost fan (or activating the ‘Operator Assist’ or ‘Automatic’ function), check the
following levels:
• fuel level (never allow the fuel tank to run out of fuel when frost fan is operating);
• oil level;
• coolant level; and
• battery voltage levels.
2.2 Conduct a visual inspection of the gear box and fan for cracks, debris, tree branches and/or birds’ nests
that might impede the operation of the frost fan.
24 New Zealand Winegrowers I nzwine.com
2.3 When performing pre-use inspections:
• always keep the tower between yourself and the fan; and
• never adjust, alter or modify any part of the frost fan.
2.4 In order to avoid toppling the tower, only authorised and suitably trained people should climb frost fan
towers.
3 WARM UP
3.1 It is essential to safely warm up a frost fan before use. Refer to the operating manual supplied by your
manufacturer for the appropriate warm up method for your machine.
3.2 If set to ‘Operator Assist’ or ‘Automatic’, the machine should engage the warm up procedure
automatically.
4 ON-SITE SUPERVISION
4.1 Always supervise a frost fan during operation.
4.2 During operation, ensure that there is access to the following:
• a set of jumper leads or spare battery;
• hand held thermometer; and
• portable fuel supply or regular delivery order from local fuel supplier.
5 DURATION OF USE
A frost fan may potentially operate for hours, after starting automatically at 1°C, even though no frost
has occurred. The 1°C frost threshold is not absolute; the risk of frost may vary by variety, time of
year, air temperature immediately preceding the temperature drop and proximity to sunrise (generally
the coldest part of the day). Assess the conditions of each frost event in order to avoid unnecessary
operation.
5.1 A frost fan should only be operated during a frost danger period.
This generally means:
• the air temperature has reached a critical level as determined by you and based on your experience of
past frost events.
5.2 Where these conditions no longer prevail and you are confident that the temperature within the
vineyard is stable, shut the frost fan down manually.
6 SHUT DOWN
6.1 When shutting down a frost fan, follow the procedure for shut down as directed by the operating
manual supplied by your manufacturer.
6.2 If set to ‘Operator Assist’ or ‘Automatic’, the machine should engage the shut down procedure
automatically.
7 ANNUAL MAINTENANCE
7.1 Ensure that the frost fan is serviced annually by a suitably qualified person.
Please note that this document does not constitute advice on how to comply with your obligations under
the Resource Management Act or your local district plan. You should check with your local Council
regarding the requirements for frost fan operation that apply in your area.
25 New Zealand Winegrowers I nzwine.com
Photo and Image Permissions
Cover: Photo courtesy of Wither Hills
Figure 1-2: Photo courtesy of Akarua Winery
Figure 3-1: Photo courtesy of Harvest
Figure 4-3: Photo courtesy of NZ Frost Fans
Figure 4-4: Diagramme courtesy of NZ Frost Fans
Figure 4-5: Fairfax Media New Zealand / Marlborough Express
Figure 4-6: Fairfax Media New Zealand / Marlborough Express
Figure 4-7: Photo courtesy of NZ Irrigation Services
Figure 4-8: Photo courtesy of NZ Irrigation Services
New Zealand WinegrowersPO Box 90-276 Victoria Street WestAuckland 1142New Zealand
The New Zealand wine industry relies on research
leading to technical innovation to enable winemakers
and grapegrowers to stay ahead in a competitive world.
New Zealand Winegrowers works to ensure its levy-
funded research programme provides and promotes a
technological basis for the New Zealand grape and wine
industry to remain internationally competitive as the
leading producer of premium quality wines.
This booklet is part of New Zealand Winegrowers’ levy-
funded research programme.
www.nzwine.com
DISCLAIMERWhile care has been used in compiling this booklet, New
Zealand Winegrowers gives no prediction, warranty or
assurance in relation to the accuracy of or fitness for any
particular purpose, use or application of any information
contained in this document. To the full extent permitted
by law neither New Zealand Winegrowers nor any of its
employees shall be liable for any cost (including legal
costs), claim, liability, loss, damage, injury or the like, which
may be suffered or incurred as a direct or indirect result of
the reliance by any person on any information contained in
this document.
© New Zealand Winegrowers 2014. All Rights Reserved.
ACKNOWLEDGMENTSThis booklet summarises New Zealand Winegrowers’
research and literature that explores the many issues
related to frost prevention and management in the
vineyard. The website (www.nzwine.com) provides a
wealth of related material, including fact sheets and
research reports, and these are highlighted in each chapter
under the heading, “More resources on nzwine.com.”
The editors gratefully acknowledge the contributions of all
the authors whose work (commissioned by New Zealand
Winegrowers) has been incorporated into this summary,
which is made possible by NZW funding. We would
also like to acknowledge the direction we have received
from Dr Simon Hooker, General Manager Research, and
the valuable technical review provided by New Zealand
Winegrowers Research Committee.