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Dry matter response (g) Dry matter response(g)
Hayward
TRUNK GIRDLING V. CANE
GIRDLING
Summer trunk girdling has proven to be a
fairly robust and successful strategy for
kiwifruit growers to increase dry matter.
Although results from 2006 above show
that there are orchards in which girdling
may not work every season, the costs of
applying girdles are very low, so even if they
are not effective, there is only minimal
fi nancial outlay for orchardists.
However, for a range of reasons, some may
choose not to trunk girdle their vines. These
reasons could include:
• Concern whether trunk girdling is
sustainable in the long term
• Believing that trunk girdling will not work
on their orchard
Fruit weight (g) Dry matter (%) Dry matter variance (% 2 )
Cane girdling (11 trials) +2 +0.5 +0.6
Trunk girdling (16 trials) +5 +0.8 -0.1
Hort16A
Cane girdling (9 trials) +2 +0.4 +0.4
Trunk girdling (7 trials) +2 +0.7 -0.3
Table 2. Average responses 1 to summer cane or trunk girdling of Hayward and Hort16A kiwifruit.
1 Responses are the difference between trunk girdled and control vines
Figure 3. Responses of Hayward and Hort16A kiwifruit to summer cane and trunk girdling in research trials
between 1999 and 2007. Response is defi ned as the difference between trunk girdled and control vines.
The number of trials is shown in brackets above each bar.
• Already achieving high dry matter and
yield via expert canopy management
and therefore no requirement for a
further boost to productivity
• No need for increases in fl owering,
which could result in increased thinning
costs
• The increased risk of harvest/postharvest
issues with advancing fruit maturity
• Vine health issues such as widespread
trunk diseases and poor root health,
preclude use of girdling.
For some of these orchardists, summer
cane girdling could be a useful alternative
(Currie et al. 2007e). But just how effective
is summer cane girdling really? To fi nd out,
we reviewed available datasets from a
range of summer trunk and cane girdling
studies conducted in New Zealand orchards
over the past nine years.
Although summer cane girdling appeared
to be somewhat effective, summer trunk
girdling consistently outperformed summer
cane girdling. For both Hayward and
Hort16A kiwifruit, the responses of fruit
weight and dry matter for trunk girdling
were almost twice as high overall (Table 2,
Figure 3). The exception was for Hort16A
fruit weight, where there appeared to be
only a small response of c. 2 g for both
types of summer girdling. This is not
surprising, as by the time summer girdles
are applied in mid February, Hort16A fruit
have typically already accumulated 80 per
cent of their fi nal weight (Minchin et al.
2003).
It was also clear from these datasets that
summer cane girdling had the disadvantage
of increasing variability (variance) of dry
matter (Table 2) as described in Currie
(2007d). This is likely to result in less
uniform fruit quality, which would not be
desirable in markets. In contrast, there was
some evidence that trunk girdling does
actually reduce variability, particularly for
Hort16A. This may be because trunk girdling
allows a “free” fl ow of carbohydrate around
the fruiting canopy, allowing fruiting canes
with excess to export to canes with less, but
without the infl uence of root competition
which could affect some fruit more than
others. In contrast, cane girdling locks
carbohydrate available within each cane,
preventing fl ow between canes.
REMINDER – VINE HEALTH
PRECAUTIONS AND GIRDLING
TECHNIQUE
We remind orchardists who are planning to
trunk girdle that precautions should be
taken to minimise any risk of introducing
vine diseases into open girdling wounds.
Any diseased vines should be marked and
avoided, and girdling tools should be
sterilised by dipping them into methylated
spirits as often as possible.
NZ KIWIFRUIT JOURNAL JANUARY / FEBRUARY 2008
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