Can we clean fruit stained from copper applications?

Transcription

Can we clean fruit stained from copper
applications?
Kiwifruit Journal May/June 2012
Shane Max and Greg Clark - ZESPRI
Growers who experienced some copper related
fruit staining from late summer applications should
avoid additional copper application and consider
®
using Citrox BioAlexin if protection is still
considered necessary. The application of fruit
cleansing sprays when copper fruit staining is first
seen may assist to clean marginal out of grade
fruit. Unfortunately, it will not improve marking on
fruit whose skin was damaged in early summer.
Light veinal damage of leaves does not appear to
be having any significant detrimental effects on the
vines performance, however, growers need to be
wary about applying repeated applications of
copper to canopies where no new growth is
occurring, as copper sprays are very persistent.
While copper products offer proven protection
against Psa leafspot, the rapid introduction of
copper sprays to our industry has resulted in some
growers experiencing problems. Typically, new
agrichemicals
require
several
years
of
experimental
field
testing
to
understand
appropriate rates, spray timing and spraying
conditions, however, the urgent need to have
effective bactericides to control Psa has meant this
was not possible. Best practice had to be
developed from what was known of other crops
and the limited experience manufacturers and
growers had had with kiwifruit here and overseas.
Eighteen months on, we are a lot more
knowledgeable on what constitutes best practice much gleaned both from various trials and grower
experiences.
While most growers managed to apply copper
without causing fruit damage, there are instances
where damage has occurred. Most of the reported
cases were when copper was applied during the
typical oil sensitive period. This was often
associated with applications of high copper rates,
immediately prior to large rainfall events and/or
slow drying. The fruit typically developed a dark
stain and/or russet on the skin. If this occurs while
the fruitlets are very small, the marking can
disappear over time – diluted by fruit growth. If it
occurs once fruit are larger, the skin russet
becomes increasingly noticeable especially when
viewed under direct sunlight.
Some applications in late summer gave fruit
staining more typical of the traditional water stain
seen in the late season. Why this is occurring is
unclear, it may be excessive copper washing off
leaves or fruit, or it may be copper interacting with
previously damaged or aging leaves forming
organic copper compounds that then deposit on
the fruit surface.
To see if it was possible to remove this stain we
investigated the effect of dipping stained, out of
grade Hayward fruit, in the laboratory in KiwiLustre
(Lactic acid and phosphate) a common fruit
cleansing spray used in the industry. We also
looked at the fruit skins under high magnification to
try to understand what damage was occurring.
The KiwiLustre solution was prepared at the same
concentration as the label rate (500ml/100l) giving
a solution with a pH of 3.5.
ZESPRI Group Limited or a subsidiary company of ZESPRI Group Limited (ZGL) makes no warranty or representation as to the accuracy or completeness of the information,
photographs or other published material (“Published Material”) in this publication. Published Material authored by a person other than ZGL reflects the view of the author and not the
view of ZGL. The Published Material may be subject to copyright and shall not be reproduced in any manner without first obtaining the written consent of ZGL. ZGL shall not be liable
to any person for loss, injury or damages arising from that person’s reliance on the Published Material. © 2012
–1–
Following dipping, the fruit was allowed to dry on
the lab bench and was assessed the next day.
While dipping did have some impact on the stained
fruit most remained similar and still out of grade
(refer to Table 1.) Interestingly, stains on fruit left in
the lab for 12 days at room temperature appeared
lighter or more ‘merged’. When brushed by hand
the majority of fruit appeared acceptable for export.
Tim Jerram from Hume Pack and Cool also
assessed fruit in a similar manner with a range of
products and concentrations. These were from fruit
damaged in December and January. His
conclusion was that, on Hayward fruit, cleansers
could remove the lighter stains off fruit, with the
best effect seen when the fruit where dipped a
second time, however, a proportion still remained
out of grade as it was more of a russet damage
than a water staining. No treatments affected the
copper damage on Gold3 or Gold9.
Table 1.
view of ZGL. The Published Material may be subject to copyright and shall not be reproduced in any manner without first obtaining the written consent of ZGL. ZGL shall not be liable to
any person for loss, injury or damages arising from that person’s reliance on the Published Material. © 2012
–2–
Close up imagery taken of the fruit prior to dipping
indicated the Hayward fruit marking appeared to
be a black marking at the base of the fruit hairs
(Table 2 – Picture b). It is likely that the hair
removal also removed some of the black colouring.
How much the time lapse between dipping and
final assessment assisted this is unknown.
However, this observation would suggest growers
experiencing copper related staining may benefit
from applying fruit cleansing sprays when the
stains are first noticed rather than immediately preharvest. It is also recommended that growers
should check their orchard for any signs of staining
prior to copper applications. Those growers who
have been utilising a copper protectant programme
through the season may be better to use Citrox
®
if further protection is deemed
BioAlexin
necessary while fruit are still on the vines.
Table 2
–3–
Leaf vein marking
The range of copper ‘brews’ put on in spring gave
a range of phytotoxicity symptoms ranging from
yellowing and leaf drop to leaf margin burn, to light
vein browning on the underside of leaves. Where
serious damage occurs photosynthesis capacity is
no doubt reduced and where this occurs on leaves
close to developing flowers and fruit, they will not
have access to the same level of carbohydrates
compared to those with healthy subtending leaves.
What was far more common, and debated more
widely, was the impact of leaf vein browning.
Table 4
Table 3
The pictures in Table 4 show where leaves have
been cut and a transect cut made across the
healthy and blackened leaf vines. It is interesting to
note, that while the top and bottom surface of
damaged veins are affected, the internal vascular
cells appear sound and are functioning. This
observation is further supported by the fact that
there are no wider leaf symptoms.
A series of pictures from an A.chinesis leaf picked
in March is shown here (Table 3 &4). A close up
shows the exterior of the vein appearing blackened
and badly affected. Note the hairiness of the leaf
under-surface. This hairiness (abundance of
trichomes) allows considerably more spray to
accumulate compared to the top-leaf surface and
may be contributing as to why the veins are more
sensitive here.
While low levels of copper phytotoxicity from
moderate copper use may not be impacting leaf
function, this would require more comprehensive
testing to confirm. Even more important is whether
spring copper applications are diminishing leaf size
and what is the flow on affect to this, if any. Trials
are planned offshore to better understand this.
Results will be reported back to New Zealand prior
to spring.
–4–
Please note, post-harvest dipping is not an
approved practice.
Acknowledgements
Thanks to Tim Jerram from Hume Pack and Cool
for his input into this article.
–5–

Can we clean fruit stained from copper applications?

Transcription

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