SunburnWhy it happens - FRESH QUARTERLY - Hortgro
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
FRESH ISSUE EIGHT
March 2020
QUARTERLY
FOR THE DECIDUOUS FRUIT GROWER
Sunburn Why it happens
& how to prevent it
FQ FQ
FQ
pUblISHER’S Letter CONTENTS
FRESH QUARTERLY
Issue 8, MARCH 2020
Copyright © 2020 Fresh Quarterly
letter from
All rights reserved. No part of this publication
may be reproduced, distributed or transmitted
in any form or by any means, including
photocopying, recording, or other electronic COVER STORY:
the Publisher
or mechanical methods, without the prior CROP PRODUCTION
written permission of the publisher, except in The world keeps warming and growers
the case of brief quotations embodied in critical are feeling the heat. In this issue we
reviews and certain other non-commercial uses discuss sunburn ̶ what is the impact 24 Keep your apples
permitted by copyright law. Address permission and what can you do about it? in the pink
This issue of Fresh Quarterly is a milestone requests to the Executive Editor at the following Research results confirm the importance
marking our first two years of publication. email address Elise-marie@hortgro.co.za. 4 Sunburn of step-down cooling in preventing
What are the different kinds? When are fruit internal browning.
What have we learnt so far and how do we
Executive editor Elise-Marie Steenkamp at risk? How do you prevent it?
plan to go forward?
Editor Anna Mouton 26 Best post-
Our original objective was to repackage past and present research results to Writers Grethe Bestbier and Anna Mouton 10 Sunburn research
summarised harvest practices
create an accessible and absorbing product for our growers. We envisaged Design and layout Megan Merifield
The protocol for Cripps Pink as developed
An overview of the highlights from
a magazine that engaged readers by a combination of compelling content Printed and distribution Media On Demand
projects funded by Hortgro Pome and CROP PROTECTION by the Store-it Group and Hortgro Science.
and attractive design. Articles had to communicate the lessons learnt Technical advisers Matthew Addison,
Hugh Campbell and Wiehann Steyn
Hortgro Stone. 16 A tale of two flies 28 Research inventory
and the benefits gained from research — the focus had to be on practical
The Mediterranean fruit fly is an old enemy
recommendations and implementation. Photography Adobe Stock Photography,
of growers. Now a new threat has appeared:
All of this still holds true. We haven’t deviated from our original objective unless specified. Cover image: Wiehann Steyn
the Oriental fruit fly. How do we fight it?
— but we’re on a journey to discover the best way to achieve it. We’ve learnt For advertising contact Thea van Zyl
that many of our readers prefer a physical magazine so we’ve decided to offer Cell +27 (0)83 642 5342, Tel +27 (0)21 870 2900 20 Going the distance
WIEHANN STEYN | HORTGRO SCIENCE
both a printed and a digital version. A copy of the printed magazine will be or Email thea@hortgro.co.za The surprising habits of Oriental fruit flies.
posted to each of our members and you will also be alerted when the digital Spoiler alert: males and females have
Hortgro Science
version becomes available for download. Welgevallen Experimental Farm, different priorities.
The implication of printing and distributing a physical magazine is an Stellenbosch, South Africa
19 Research inventory
increase in production cost. We’ve chosen to allow a limited number of Postal Address PO Box 12789, REGULARS
advertisements in the Fresh Quarterly to cover these costs. We hope that Die Boord, 7613
POST-HARVEST 2 Letter from the Publisher
these advertisements will also add value by alerting our readers to useful Tel +27 (0)21 870 2900/01
products and services. Fax +27 (0)21 882 8966 22 Internal browning 29 COLUMN - A citrus
The success of Fresh Quarterly depends on its relevance to our members. Email hortgroscience@hortgro.co.za in Cripps Pink perspective on Oriental fruit fly.
Please get in touch to share your suggestions — we welcome your feedback. www.hortgro-science.co.za 12 Net essentials A post-harvest expert explains the 30 COLUMN - Back to earth.
Pome and stone fruit production under nets difference between diffuse and radial
Hugh Campbell,
is surging ̶ but are nets appropriate for browning ̶ and why it matters.
all orchards? Six people across the industry
provide answers.
9 Research inventory
2 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 3
FQ CROP PRODUCTION
Sunburn can
cause significant
economic losses
Sunburn is the damage
caused by too much sun exposure — anyone
sunburn. It can go up to 30%, sometimes
even more than that.”
Heat — not light — causes the tissue
damage and death. Sunburn necrosis can be
in apples and who spends time outdoors knows this. People Stone fruit are also susceptible to experimentally induced in complete darkness
other fruit.
Why it tend to find a tan attractive in humans
but not so much in apples and other fruit.
sunburn. Prof. Karen Theron holds the
Chair in Applied Preharvest Horticulture at
by raising fruit surface temperature.
Sunburn browning is the equivalent of
happens
Sunburn is a major reason why fruit is Stellenbosch University. “There are seasons a tan. The fruit responds to excess light
rejected as unsuitable for export and ends up when there are sunburn problems in certain and heat by developing yellow, brown,
in informal markets or as juice. plum cultivars,” she confirms. bronze or dark discolouration of sun-
& how to “Sunburn is most noticeable in pome
fruit,” says Prof. Stephanie Midgley of the
Sunburnt fruit frequently suffer from
post-harvest disorders because of the role
exposed areas of the peel. The underlying
flesh is not damaged. Affected fruit can
prevent it.
Department of Horticultural Science at of heat stress in both sunburn and many have higher sugar levels and lower acidity
Stellenbosch University. The worst-affected post-harvest problems. but consumers dislike sunburn browning.
apple cultivars are Granny Smith, Golden Anything more than mild discolouration
By Anna Delicious and Fuji.
The impact of sunburn on sensitive
The sunburn spectrum
Sunburn is a collective term for three
will lead to rejection by the market.
Both light and heat are necessary for
Mouton
cultivars is significant, according to preharvest conditions that differ in ways that sunburn browning — it will not develop
Sunburn
Midgley. “In my experience an average are relevant to control. The descriptions below in darkness. Apple cultivars vary in their
orchard that is well-managed and not under refer to apples but similar conditions can sensitivity to browning. The dark colours of
drought stress will often have 10%–15% occur in other fruit and even some vegetables. certain red apple and stone fruit cultivars
Sunburn necrosis is the most dramatic may also mask browning.
manifestation of sunburn. Affected fruit The third type of sunburn is called
have dark brown or black areas of dead photooxidative sunburn. It affects fruit
tissue on the surface. The damage may that are suddenly exposed to sunlight after
extend for several millimetres into the flesh having grown in shaded conditions. This
and is a perfect substrate for the growth can happen due to management practices
of spoilage organisms. Sunburn necrosis such as summer pruning or even when
renders fruit unfit for anything other than newly picked fruit are left lying in full
perhaps juicing. sun. Light exposure — not heat — is the
Research has shown that sunburn necrosis primary driver of photooxidative sunburn.
occurs when the fruit surface temperature Fruit affected by photooxidative sunburn
attains 52 °C for as little as ten minutes. develop a white — or photobleached —
STEPHANIE MIDGLEY | STELLENBOSCH UNIVERSITY
4 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 5
FQ CROP PRODUCTION
Sunburn browning and
necrosis tend to occur
area. Tissues in the centre of the bleached
area may eventually die off and the fruit is
on fruit that are at least
left with a necrotic area similar to that seen
in sunburn necrosis. 45 millimetres in diameter.
Sometimes fruit only develop signs
of sun damage while in storage. Minor
sunburn browning at harvest can progress to
extensive darkening in Granny Smith apples
during storage. This is called sunburn scald
or sunscald. Sunscald — like all scalds — is a Sunburn necrosis is characterised
post-harvest disorder. Sunscald develops on by a well-circumscribed, dark
Photooxidative
HELEN MARAIS | STELLENBOSCH UNIVERSITY
the exposed side of the fruit whereas other brown or black area of dead tissue
on the fruit surface.
scalds tend to develop on the shaded side. H
sunburn can
EL
EN
M
Factors that contribute to sunburn
AR
AI
afflict fruit of
S|
Temperature and sunlight are the main
S TE
culprits — as described above — but there
LLE
NBO
any size.
are several indirect factors that also influence
SC H U
the development of sunburn. One of these —
NIVERSITY
cultivar — has already been mentioned. widespread with the trend toward high-
Individual fruit within a cultivar respond density plantings. “What I saw in Australia
Photooxidative sunburn has
differently to sun exposure. Some fruit was that every single one of those orchards
resulted in bleaching of the
— like some people — just never seem to colour on the exposed surface where they’re doing two-dimensional
burn. Scientists are still trying to work out of these apples. not acclimated and they will burn if suddenly that are east-west and plantings has shade net,” states Midgley.
the reasons for this individual variation. exposed during summer pruning. For this when you walk through “There would have to be research done
Sunburn browning and necrosis are more reason summer pruning is best done as soon them there’s no sunburn here where we have a very two-dimensional
common in fruit that are at least 45 as possible after final fruit set or when doing on the south. But there’s planting to see how that changes the risk
millimetres in diameter. Photooxidative final hand-thinning. sometimes serious sunburn on for sunburn. To be absolutely safe one
sunburn can afflict fruit of any size. The trend toward high-density the north.” would advise farmers to put up a net if they
Fruit are at risk of sunburn above a that heats or cools the fruit. Low relative plantings of smaller trees on dwarfing Researchers have tested a number of want a system like that.”
threshold fruit surface temperature. humidity may promote sunburn by rootstocks increases the risk of sunburn interventions for sunburn. Theron recalls The inexorable rise in global temperatures
The threshold is higher in fruit that are increasing fruit surface temperature. Air due to increased light exposure. Dwarfing experiments with kaolin as a sunblock. “Yes, “And in plums you have the problem are leading us to a hotter and drier future
acclimated to the sun. All fruit are capable movement can retard sunburn by decreasing rootstocks may also predispose trees to it reduces sunburn, but if you don’t wash it off that the fruit often burst if you apply where sunburn and related disorders can
of acclimation — given sufficient time. fruit surface temperature. Even modest air drought stress if irrigation is not well- one hundred percent, it looks as though there’s evaporative cooling close to harvest.” only become more troublesome. Canopy
Apples that set and grow in sunlight can circulation can cool fruit by 4–5 °C. managed because their root systems are spray residues on the fruit, which is most Shade net has proved the most practical management and shade nets will play an
tolerate far more light and heat than smaller. Optimal irrigation is important in definitely not acceptable to the market.” option for combatting sunburn. “When important role in helping growers to safeguard
those that have lived all their life in the Strategies to reduce sunburn mitigating the risk of sunburn but there is Midgley adds that see-through we did the trials almost ten years ago, it their production in years to come.
cool shade. Apples that have experienced “The main thing that farmers want to do is no benefit in over-irrigating the trees. sunscreen products were also trialled but was absolutely clear that there’s almost
a long period of overcast weather may be canopy management,” says Midgley. Fruit Correct row orientation will help reduce never caught on. no sunburn under shade net,” confirms Reference: Racsko J. and Schrader L.E.
vulnerable to sunburn if the days suddenly that were exposed to sunlight from a small sunburn. “In South Africa the standard Evaporative cooling is effective at Midgley. “The intensity is reduced and 2012. Sunburn of apple fruit: historical
turn bright and hot. size have had time to acclimate and build up is north-south for that reason,” explains reducing sunburn but it’s not a viable the numbers are really low. So that’s what background, recent advances and future
Fruit surface temperature influences their defences against strong light and high Midgley. “It’s actually a little off north- solution for South Africa. “We don’t have people are using.” perspectives. Critical Reviews in Plant
sunburn and therefore so does anything temperatures. Fruit that have been shaded are south. There are still orchards out there enough water to use this,” says Theron. Shade net is likely to become even more Sciences 31(6):455‒504.
6 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 7
FQ CRop pRodUCtIon
RESEARCH Current projects
Labuschagne IF, Louw ED, Booyse M, Truter W,
foliar S-ABA application as an apple sunburn
suppressant explained through effects on peel
InVEntoRY
Hörstmann and Van Zyl W. Adaptability indexing biochemistry and leaf ecophysiology. Scientia
of new pome (apple) and stone fruit (plum) Horticulturae 232:256–263.
cultivars in diverse South African growing areas. Wand SJE, Theron KI, Ackerman J and Marais
A list of research projects Midgley SJE, Dzikity S, Volschenk T and SJS. 2006. Harvest and post-harvest apple
and publications related Lötze E. Investigating the potential of fixed and
draped netting technology for increasing water
fruit quality following applications of kaolin
particle film in South African orchards. Scientia
to sunburn and funded productivity and water savings in full-bearing Horticulturae 107:271–276.
Sunburn by Hortgro Pome and apple orchards under micro-irrigation.
Midgley SJE, Shülze RE and Davis NS. Scientific Conference proceedings
Hortgro Stone.
browning Completed projects
and practical guide to climate change and pome/
stone fruit production in South Africa.
Theron KI. Effect of nets on growth, yield and
Barasu PD, Steyn WJ, Schmeisser M and
Midgley SJE. (In press). Sensitivity of apple
causes yellow
(Malus domestica Borkh.) fruit peel to high
2003. Midgley SJE, Holcroft DH, Jacobs G and fruit quality as well as economic feasibility in plums. irradiance and temperature as influenced by
Steyn WJ. Improving red colour development
a range of rootstocks in South Africa. Acta
to brown Publications
in blushed apples. [The project assessed
Hortic. Proceedings of the 30th International
evaporative cooling.]
Journal publications Horticultural Congress, Istanbul, Turkey, 12–16
discolouration
Fouché JR, Roberts SC, Midgley SJE and Steyn WJ. August 2018.
2006. Midgley SJE, Gindaba J, Theron KI, Holcroft
2010. Peel color and blemishes in Granny Smith Le Grange M, Wand SJE and Theron KI. 2004.
DH, Jacobs G, Steyn WJ and various MSc
apples in relation to canopy light environment. Effect of kaolin applications on apple fruit quality
on the fruit
students. The influence of climate stress and
HortScience 45(6):899–905. and gas exchange of apple leaves. Acta Hortic.
source/sink manipulations on gas exchange, size
Gindaba J and Wand SJE. 2005. Comparative 636:545–550.
and colour development of bi-colour apples.
surface.
effects of evaporative cooling, kaolin particle film Gindaba J and Wand SJE. 2008. Comparison
[Included studies on nets and particle films.]
and shade net on sunburn and fruit quality in of climate ameliorating measures to control
apples. HortScience 40:592–596. sunburn on ‘Fuji’ apples. XXVIIth International
2010. Steyn WJ, North M, Cook NC, Midgley
Gindaba J and Wand SJE. 2007. Do Horticultural Congress, August 2006, Seoul,
SJE and various MSc students. Improvement of
fruit sunburn control measures affect leaf Korea. Acta Hortic. 772:59–64.
apple colour.
photosynthetic rate and stomatal conductance Makeredza B, Jooste M, Lötze E, Schmeisser M
in ‘Royal Gala’ apple? Environmental and and Steyn WJ. 2018. Canopy factors influencing
2011. Brink D, Pretorius JJB and Steyn WJ.
Experimental Botany 59: 160–165. sunburn and fruit quality of Japanese plum
Developing a sunburn control strategy for Granny
Hengari S, Theron KI, Midgley SJE and Steyn WJ. (Prunus salicina Lindl.). Acta Hortic. 1228:121–128.
Smith, Fuji and Braeburn using Raynox Plus.
2014. The effect of high UV-B dosage on apple Mupambi G, Reynolds JS and Steyn WJ.
fruit photosystems at different fruit maturity 2014. Foliar S-ABA application does not reduce
2014. Brink D, Kotze WP and Steyn WJ. The
stages. Scientia Horticulturae 170:103–114. sunburn in ‘Granny Smith’ apple. Acta Hortic.
effect of different coloured shade nets on the
Hengari S, Theron KI, Midgley SJE and Steyn 1042:303–309.
productivity of Granny Smith and Fuji apple trees
WJ. 2014. Response of apple (Malus domestica Mupambi G, Schmeisser M, Lötze E, Malan
in the EGVV area.
Borkh.) fruit peel photosystems to heat stress C, Dzikiti S and Steyn WJ. 2017. Effect of
coupled with moderate photosynthetic active supplementary irrigation at high ambient
2015. Steyn WJ, Midgley SJE, Lötze E, Schmeisser
radiation at different fruit developmental stages. temperatures on sunburn, plant physiology,
M, Theron KI and students. Inherent and acquired
Scientia Horticulturae 178:154–162. soil and canopy environment of ‘Granny Smith’
resistance to fruit sunburn and poor colour in
Hengari S, Theron KI, Midgley SJE and Steyn apple. Acta Hortic. 1150:239–244.
various apple/pear cultivars.
WJ. 2016. Differential dependence of apple Smit A, Steyn WJ and Wand SJE. 2008. Effects
(Malus domestica Borkh.) cultivars on the of shade netting on gas exchange of blushed
Jacques Fouché | stellenbosch university
Jacques Fouché | stellenbosch university
2017. Steyn WJ, Dzikiti S and Schmeisser M. Tree-
xanthophyll cycle for photoprotection. South apple cultivars. Acta Hortic. 772:73–80.
water relations and sunburn in pome fruit.
African Journal of Plant and Soil 33(1):69–76. Wand SJE, Steyn WJ, Holcroft DH, Mdluli
Makeredza B, Marais H, Schmeisser M, Lötze MJ, Van den Dool K and Jacobs G. 2005. Use of
2018. Midgley SJE and Steyn WJ. Acclimation
E and Steyn WJ. 2015. Ripening associated red evaporative cooling to improve ‘Rosemarie’ and
of apple peel to light and temperature and the
color development masks sunburn browning in ‘Forelle’ pear fruit blush colour and quality. Acta
effect thereof on red colour development and
apple peel. HortScience 50(6):814–818. Hortic. 671:103–111.
tolerance to sunburn.
Makeredza B, Schmeisser M, Lötze E and Steyn Wand SJE, Van den Dool K, Smit A and Steyn
WJ. 2013. Water stress increases sunburn in WJ. 2008. Heat injury thresholds in apples
2019. Steyn WJ, Jooste M, Schmeisser M and
Cripps Pink apple. HortScience 48(4):444–447. measured using chlorophyll fluorescence
Lötze E. Heat damage in plums.
Mupambi G, Schmeisser M, Dzikiti S, Reynolds are influenced by orchard heat reduction
S and Steyn WJ. 2018. Ineffectiveness of technologies. Acta Hortic 772:273–277.
8 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 9
FQ CROP PRODUCTION
Hortgro Pome and Hortgro Stone have funded ̶
and continue to fund ̶ extensive research into the
development and control of sunburn. The goal is to
better understand the causes and mechanisms of
sunburn so that control measures can be developed.
This article summarises some of the highlights.
Consult the research inventory for more on the many
scientists involved and their research outputs.
The development of sunburn
is thought to be associated with both heat
exposure and UV-B irradiation. Laboratory
to the control, irrigation at twice normal
levels did not reduce sunburn compared to
the control.
The red colour of apple cultivars such as
Topred and Cripps Pink may mask sunburn
browning. Studies confirmed that red
trials showed that different cultivars respond Research on the effect of pulsing and blushed cultivars are not protected
differently to UV-B but all are more sensitive irrigation in apples was inconclusive. from sunburn by anthocyanin — the red
to UV-B if they have been growing in the Pulsing irrigation improved the plant water pigment just hides the sunburn. Analysis
Sunburn
shade. The researchers confirmed that status and reduced sunburn in Granny of the tissue response of different cultivars
photodamage in acclimated fruit starts at Smith and Golden Delicious compared revealed that the severity of visible signs
temperatures of around 45 °C. to a control that did not receive pulsing of sunburn is not directly correlated to the
Sensitivity to sunburn was tested for Rosy irrigation. However, the control experienced stress levels of the fruit.
research
Glow apples grown on a range of dwarfing water deficits. Therefore the difference in Sunburnt fruit tend to have higher
to vigorous rootstocks. The researchers the occurrence of sunburn could reflect sugar levels but higher sugar levels do
concluded that the rootstock does not affect increased sunburn in the control rather not predispose fruit to sunburn. Fruit do
the innate sensitivity of the apple peel than a true decrease in the treatment. become more sensitive to sunburn closer
summarised
to high light and temperature. Sunburn Researchers measured the colour of to harvest for a large variety of reasons but
prevalence on a tree level is likely to be Granny Smith apples at different positions high sugar levels are not one of the causes.
driven by the exposure of more fruit to in the canopy from fruit set until harvest Two years of trials on Braeburn,
potentially damaging levels of light and heat. to see how colour and sunburn relate to Fuji, Royal Gala and Cripps Pink apples
Water stress was found to increase light levels and fruit surface temperature. demonstrated that 20% black shade net
fruit surface temperature and sunburn They found that Grannies require good light was not detrimental to photosynthesis and
HELEN MARAIS | STELLENBOSCH UNIVERSITY
in Cripps Pink and Granny Smith apples until around eighty days after full bloom carbon assimilation rates. The implication
as well as in African Delight and Laetitia to develop high chlorophyll concentrations is that nets will not have a negative effect
plums. Researchers tested various levels and dark green colour. Too much light in on seasonal carbohydrate production and
Highlights of of irrigation against normal irrigation for the latter half of the season reduced green growth. Nets with a high shade percentage
projects funded by different time periods in a series of trials. colour and increased the risk of sunburn may have a negative effect on the extent
Sunburn was both more prevalent and more and red blush. These results indicate that and intensity of red colour.
Hortgro Pome and severe in fruit from trees suffering from shade netting — especially draped nets — Plums are susceptible to sunburn and
Hortgro Stone water stress. Whereas irrigation at half should significantly improve the colour of internal heat damage. Shade net and
normal levels increased sunburn compared green apple cultivars. optimal irrigation reduced sunburn.
ISSUE 08 MARCH 2020 FQ 11
FQ CRop pRodUCtIon
Net esentials
Pome and stone fruit production under
Wiehann Steyn | hortgro Science
nets is surging ̶ but are nets appropriate
for all orchards? Fresh Quarterly spoke to
six people across the industry about their
practical experience of using nets.
Do you need nets?
“You need to determine the commodity and the Brink contrasts nets for hail with nets for suggests — draped over trees instead of data from trials he conducted with draped Retractable nets are supported by
purpose. You can put nets up for hail and sleet, sunburn. “You want hail nets to transmit being supported by posts and wires. nets on Granny Smith apples. permanent structures but can be
opened or closed.
or for sunburn, or for wind damage,” says Charl as much light as possible because they’re Sunburn can also affect plums but the “If your yield was around sixty tonnes,
Stander, agricultural consultant at Franschhoek usually covering high-value crops for primary driver for using nets in plums is you could make an additional R100 000.00
Marketing. “The pioneering work on nets was most of the season and you don’t want to often wind damage. “I’ve erected about per hectare with your nets, which is roughly
done in the northern parts of South Africa, influence the red colour. For sunburn on fifteen hectares of nets to prevent wind the cost of the draped nets You pay for the
primarily for hail in peaches and nectarines.” green varieties you want a dark net so you damage,” remarks horticultural adviser net in one year and it lasts twelve to fifteen have a higher production because the trees
Most people agree that nets are essential in can prevent as much sunburn as possible.” Petru du Plessis of his own orchards in years. The question isn’t how much it costs, are larger.“
areas where hail and sleet occur. “If you don’t Sunburn can reduce the yield of export- Stellenbosch. Nets have increased his yield but how much money I’ll get back.” The downside of too much growth in
erect hail nets, you may as well give up,” asserts quality fruit to as little as 40% in susceptible of export-quality fruit by 10%–12%. Orchards under nets require careful older trees is reduced yield. “Farmers who
What you need to Daan Brink, technical adviser at Fruitmax Agri. cultivars such as Granny Smith. “Put a net management as the trees grow more are considering nets must implement
know to get started. Hail nets tend to be fixed nets — these
are nets that are supported by permanent
up and you can shift your pack-out to 85%,”
says Brink, “and your fruit quality improves
What are the challenges?
Cost is an obvious drawback. But there
vigorously. This is a potential advantage
when establishing orchards under fixed
very good summer pruning,” advises Du
Plessis. “I think anyone who uses nets and
By Anna Mouton structures. The nets are usually pitched over dramatically. The fruit is greener.” is general agreement that nets pay for nets. “The growth you get from your trees doesn’t have optimal summer pruning will
the rows to encourage the hail to fall to the Nets for sunburn can be either fixed or themselves when they are used appropriately. is substantially better,” says Brink. “The day eventually run into fertility problems.”
ground instead of accumulating on the nets. draped. Draped nets are — as the name Horticultural adviser Anton Müller shares that the trees come into production, you The effect of nets on colour development
12 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 13
FQ crop production
to keep them in place. So could they be a Fixed nets are supported
better option than fixed nets for sunburn? by a permanent structure
of posts and wires. Draped nets
It depends, says Müller. “If you’re in the
are supported
Grabouw area there’s no real reason for a fixed
by the tree itself.
can be positive — think greener Grannies — structure. You only need to control sunburn
or negative. Brink warns that you sacrifice at certain times of the year. But for hail you
red colour in bicolour apples, although less need nets for a much longer period.”
so with white or translucent nets. “Your Draped nets are especially valuable for older
production gains have to be enough to trees. Müller recounts that his initial research
justify that loss of colour,” he says. Some into draped nets was prompted by old Granny
growers also report that apples are slightly Smith trees. “Their harvest was lost because of
smaller under nets. Brink believes this could sunburn and everyone was saying you should
be due to over-irrigation, insufficient fruit take them out. But the market is clamouring
thinning or increased tree vigour. for Grannies. With a net we can keep those
BOTH PHOTOS BY WieHann STeYn | HOrTgrO Science
Colour development in plums can likewise orchards for many more years.”
be less intense under nets. However fruit
tend to be larger.
“Bees and
To fix or not to fix
The majority view is that fixed nets are the nets are not
preferred option for protection against hail
and wind damage. Both fixed and draped nets compatible.”
are suitable for controlling sunburn.
Fixed nets are available as so-called Does net colour matter?
retractable nets that can be pulled back to Professor Wiehann Steyn, research
expose trees to full light. Retractable nets are and development manager at Hortgro
more expensive than non-retractable nets. Science, recommends that growers stick to
Retractable nets are the recommended monochromatic nets — black, grey, white “Nets will play a much more prominent role, given the drought in the Klein-Karoo
option for trees that require pollination by
bees. “Bees and nets are not compatible,”
and translucent. The difference between these
shades is the amount of light they let through.
Pest control under nets
“If there is a pest and you cover it with a
and the growers that need to generate income. If water is limiting your new plantings
says Stander. Nets also impact the quality
of flower buds and this can lead to reduced
Steyn stresses that growers need to be clear
about the problem that the net is intended to
net, it will cause problems,” warns Brink.
“You need more monitoring. But you don’t
then you have to increase the yield of what you have. You have to increase your pack-
fertility and yields over several seasons. solve. Is it sunburn on Grannies? Consider a necessarily need to spray more.” Fixed nets outs and how do you do that? By reducing wind damage and sunburn.”
Stander advocates retracting the nets black net. Worried that a black net will reduce improve spray conditions and can facilitate
immediately after harvest and leaving the the productivity of your Goldens? A grey net pest control. It is possible to spray effectively problems have occurred in the past with trees and we lost productivity. Now that Commission indicate savings of only 12%.
trees exposed until pollination is complete. may be a better option. And for damage that through draped nets by using higher air chemicals transferring from crates to fruit. we’re on the right rootstocks we can put the “This was in the mild Witzenberg valley,”
“If you have fixed nets that can’t open, they isn’t caused by light — for example hail — volume settings. trees under nets.” reports Steyn. “Savings tend to be greater
need to be fairly high,” cautions Stander. This look at white or translucent nets. Fruit flies and codling and false codling What lies ahead for nets? He describes the next challenge as under more extreme conditions.”
allows room for bees to move over the rows. “The one thing we’ll have to keep in mind moths appear to be less numerous under nets. Everyone agrees that the number of orchards sourcing trees in the numbers that he Stander is positive about the expansion
Growers who experience snow should in future is the environmental impact,” Growers need to be aware that chemicals under nets will proliferate further. But, as needs to establish new orchards under nets. of nets. “Nets will play a much more
also invest in retractable nets. “We made says Steyn, “the visual impact.” The Italian break down more slowly under nets. “The Kotze points out, there are some constraints. “We’re reliant on the right rootstocks and prominent role, given the drought in the
the mistake of not having retractable nets province of South Tyrol allows only black market is fanatical about residues,” cautions “This is a growing industry and there’s a this is likely to limit the expansion.” Klein-Karoo and the growers that need to
where there’s snow,” recalls Willie Kotze, nets for aesthetic reasons. “Black is a little Stander, “so you must adapt to ensure that shortage of contractors to erect nets. And Climate change is set to boost net use generate income. If water is limiting your
technical adviser at Dutoit Agri. “You have extreme for our blush cultivars. Grey is a you stop spraying a few days earlier.” there aren’t enough dwarfing rootstocks.” even more. Everyone agrees that nets new plantings then you have to increase the
the risk of the whole structure collapsing. potential compromise between the visual Stander also raises concerns about Kotze explains that the success of lower the water requirements of trees — yield of what you have. You have to increase
That’s not much fun.” disturbance of white nets and too much potential residues in draped nets. “If the apple trees under nets relies on dwarfing but by how much? Work done in Australia your pack-outs and how do you do that? By
Draped nets are supported by the tree itself shade cast by black nets.” spray accumulates in the nets and it touches rootstocks. “We tested nets in the past but found reductions of up to 25% but a study reducing wind damage and sunburn.”
and don’t require an expensive structure the fruit it could leave a residue.” Similar we could never control the growth of the funded by Hortgro and the Water Research
14 FQ ISSUE 08 MARCH 2020 iSSuE 08 MArcH 2020 FQ 15
Two Flies
FQ
CROP PROTECTION
A TA L E O F
How Oriental fruit flies globe, including to South Africa. Currently,
differ from Mediterranean Mediterranean fruit flies are found in most
parts of South Africa.
fruit flies. By Grethe Bestbier Both Oriental and Mediterranean fruit
The Mediterranean fruit fly has long been flies have a typical fruit-fly life cycle: the
established across South Africa and now female and male mate; the female lays eggs
a new kid on the block has appeared: the under the skin of fruit; the larvae hatch
Oriental fruit fly. While both Mediterranean and feed on the fruit; the final larval stage
and Oriental fruit flies cause their fair jumps into the soil where it pupates; the
share of damage, the latter is a different adult emerges from the soil. This process
type of trouble. Known for its aggression, takes about a month under optimal
competitiveness and rapid reproduction, the conditions of 25°C and slows down in
Oriental fruit fly might pose the bigger risk to winter. Fruit flies do not become dormant
South Africa’s deciduous fruit industry. during cold months, but overwinter as
adults or larvae. Because fruit flies are
Different journeys but similar polyphagous and attack a wide variety of
life histories fruit, there is usually an available host, no
The Oriental fruit fly (Bactrocera dorsalis) matter the season.
and the Mediterranean fruit fly (Ceratitis
capitata) underwent different journeys to The pit bull versus the chihuahua
South Africa. Originally from Asia, the The Oriental fruit fly is a tropical insect that
The Oriental fruit fly
Oriental fruit fly was first discovered on the prefers tropical fruits like mangoes, but it ̶ Bactocera dorsalis ̶
African continent in Kenya in 2003. From can also infest deciduous fruit, including resembles a wasp but is
there, the pest spread south. In 2013, it nectarines, plums, apples and pears. much smaller.
invaded South Africa. Today, Oriental fruit “We wanted to know whether Oriental
fly is officially established in the northern and Mediterranean fruit flies could use
and northeastern parts of the country, but the same hosts,” says Dr Welma Pieterse,
not in the Western Cape or Langkloof. an entomologist with the Department
Mediterranean fruit fly, on the other of Agriculture, Land Reform and Rural
hand, is established over a wider area. Development. “The conclusion is that both
It is believed to originate from tropical fly species can complete their life cycles on
Africa and invaded Europe more than 150 various deciduous hosts. In fact, Oriental
years ago. From there it spread across the fruit flies can do it more efficiently.”
16 FQ ISSUE 08 MARCH 2020
FQ CROP PROTECTION
The Mediterranean fruit fly
Environmental Entomology, 42(5):831‒40.
̶ Ceratitis capitata ̶
is established throughout Dufourd C, Weldon C, Anguelov R and Dumont
South Africa. Y. 2013. Parameter identification in population
models for insects using trap data. Biomath,
“We don’t know how it will RESEARCH
2: 1312061.
Grout TG, Daneel JH, Mohamed SA, Ekesi
respond to a Mediterranean INVENTORY
S, Nderitu PW, Stephen PR and Hattingh V.
2011. Cold susceptibility and disinfestation of
climate. But, as we speak, A list of research projects
Bactrocera invadens (Diptera: Tephritidae)
in oranges. Journal of Economic Entomology,
and publications related
those insects are busy to Oriental fruit fly and
104(4):1180‒8.
Hill MP and Terblanche JS. 2014. Niche
funded by Hortgro Pome
adapting, and we know that and Hortgro Stone.
overlap of congeneric invaders supports a
single-species hypothesis and provides insight
insects adapt quickly.”
into future invasion risk: implications for global
Completed projects management of the Bactrocera dorsalis complex.
2008. Addison P and Marakhan A. Pest risk PLoS ONE 9(2): e90121.
analysis of fruit fly introductions and assessment Karsten M, Barton M, Addison P, Addison
Oriental fruit flies easily outcompete Oriental fruit flies have other strategies it as a survival host. Because it is a thick and of current fruit fly management practices. MF and Terblanche JS. 2018. A synthesis
other flies. Pieterse says that while as well. When the females probe fruit with sturdy fruit, pupae can possibly survive in it 2011. Grout T. Cold susceptibility and for managing invasions and pest risks
observing both species for her research, the their ovipositors, they deposit pheromones over the winter. Then, when more suitable disinfestation of Bactrocera invadens (Diptera: simultaneously for tephritid fruit flies in South
Oriental fruit flies’ hostility was striking. that deter other flies from infesting that temperatures and crops appear, it can live Tephritidae) in oranges. Africa. Entomologia Experimentalis et Applicata.
“They are incredibly aggressive. They host. Lastly, Oriental fruit fly larvae hatch on in the preferred hosts. In that way, the 2014. Terblanche JS and Hill MP. Bactrocera 166 (5):344‒356.
pushed and shoved each other,” she says. earlier than Mediterranean fruit fly larvae, population is sustained,” says Pieterse. dorsalis environmental niche modelling. Makumbe LDM, Manrakhan A and Weldon
“The Mediterranean flies mostly kept out which gives them a competitive edge. The Addison believes that the Oriental fruit 2015. Pringle KL. Bactrocera dorsalis: pest risk CW. 2017. Optimisation of fluorescent pigment
of the way while the Oriental flies patrolled earlier larvae hatch, the better their chances fly’s potential to establish in deciduous analysis for the deciduous fruit industry in the marking for Bactrocera dorsalis (Diptera:
the fruit.” in the fruit. fruit production areas in the Western Southwestern Cape. Tephritidae). African Entomology, 25:220‒234.
It is not only their aggressive nature that Cape is very high. “Climatic models, the 2017. Weldon C. Dispersal capacity of Bactrocera Manrakhan A and Addison P. 2014. Assessment
makes the Oriental fruit fly the pit bull and Oriental fruit fly’s apple fetish Oriental fruit fly’s ability to compete with dorsalis. of fruit fly (Diptera: Tephritidae) management
the Mediterranean the chihuahua in this While nectarines proved to be the best host Mediterranean fruit fly, and its suitability 2019. Addison P and Pieterse W. Forecasting practices in deciduous fruit growing areas in South
fight. The former is also a better invader in for both fly species in laboratory studies, for deciduous hosts, indicate that it could Bactrocera dorsalis invasion potential using trait- Africa. Pest Management Science, 70(4):651‒60.
terms of reproductive rate. apples were surprisingly popular with do well.” However, she warns that these based modelling approaches. Pieterse W, Benítez HA and Addison P.
“An invasive insect wants to fit in as Oriental fruit flies. “We weren’t expecting are predictions based on a controlled 2017. The use of geometric morphometric
many generations in a year as possible, Oriental fruit flies to do so well on apple, laboratory study. “We don’t know how it Current projects analysis to illustrate the shape change induced
so being able to reproduce quickly is because it is far removed from a tropical will respond to a Mediterranean climate. Ware T. Cold sterilization treatments for by different fruit hosts on the wing shape
advantageous,” explains Prof. Pia Addison fruit,” says Addison. “But, it did really well. But, as we speak, those insects are busy Bactrocera dorsalis in deciduous fruit. of Bactrocera dorsalis and Ceratitis capitata
of the Department of Conservation Ecology The reproductive rate was high on apple adapting, and we know that insects (Diptera: Tephritidae). Zoologischer Anzeiger,
and Entomology at Stellenbosch University. compared to Mediterranean fruit fly. adapt quickly.” Publications 269:110‒116.
Pieterse’s research found that various Pieterse observed both species on apples for “Early detection and elimination Anguelov R, Dufourd C and Dumont Y. 2017. Pieterse W, Manrakhan A, Terblanche JS and
factors enable Oriental fruit flies to reproduce ninety days in the laboratory. By the end of of Oriental fruit flies are of utmost Simulations and parameter estimation of a trap- Addison P. 2019. Comparative demography
faster than Mediterranean fruit flies. Oriental the experiment, the Oriental fruit flies were importance,” emphasises Pieterse. insect model using a finite element approach. of Bactrocera dorsalis (Hendel) and Ceratitis
fruit flies live longer as adults, so can lay eggs still very active and laying eggs. Apples seemed “Monitoring is crucial, because on Mathematics and Computers in Simulation, capitata (Wiedemann) (Diptera: Tephritidae)
for longer and thus generate more offspring. to extend the Oriental fruit fly’s lifespan, deciduous fruit they can sustain their 133:47‒75. on deciduous fruit. Bulletin of Entomological
They also attempt more oviposition and lay especially compared to the Mediterranean fruit population. To avoid establishment in the De Villiers M, Manrakhan A, Addison P and Research, 27:1‒10.
more eggs than Mediterranean fruit flies. fly. Relative to other fruit, however, apple is Western Cape, we must be extra careful Hattingh V. 2013. The distribution, relative
Female Oriental fruit flies lay around fifty not the number one host. here. Monitoring systems, traps, and people abundance, and seasonal phenology of
eggs over ninety days — about twice as many “Apple is definitely not their primary who check it regularly, are important to Ceratitis capitata, Ceratitis rosa and Ceratitis
as Mediterranean fruit flies. host, but they will most likely be able to use know what is going on.” cosyra (Diptera: Tephritidae) in South Africa.
18 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 19FQ CROP PROTECTION
GOING Temperature and rainfall
The Distance
According to Weldon, South Africa has
favourable environmental conditions for
Oriental fruit flies to disperse, especially
in terms of temperature. His team found
Factors influencing dispersal in that the frequency and duration of flight
Oriental fruit flies. By Grethe Bestbier
increases in the optimal range of 24°C to
“ the
At
32°C. When temperatures drop below 20°C,
flies become relatively inactive, while very
hot conditions — 36°C and above — increase
moment the Western “The young males have this tendency to duration of resting.
Cape is an Oriental fruit fly free area and we want to move away from the place where “The temperature [in South Africa] is
want to maintain it like that,” says Prof. Chris they emerged,” says Weldon. “There seems only below the threshold of 20°C in the
Weldon from the Department of Zoology and to be a pattern where the males disperse evening or in the early morning. After that,
Entomology at the University of Pretoria. “If when they are young, whereas older males during the most of the day, the temperature
you want to keep Oriental fruit flies out of the settle down.” conditions for flies are great, unless it gets
Western Cape, then you need to know what However, this is not the case for females. too hot,” says Weldon.
is driving them, why and where they want to The distances that females fly is determined The impact of rainfall is still uncertain.
move, and what determines how far they fly.” by the availability of host plants. Females Although there were no clear effects on
Weldon explains that knowledge of are stronger fliers when released amongst dispersal, increased rainfall did result
dispersal can be used to establish buffer non-host plants. in more female recaptures. One possible
zones. These are areas from which fruit “Because females lay their eggs in the explanation is that rainfall increases
should be excluded to avoid fruit fly invasion. developing fruit on host trees, we suspect humidity and females prefer humid
Then again, if the pest does establish in the that they are less likely to move away from environments, becoming more active and
Western Cape, dispersal ability will determine host plants. But if they are in a place with more likely to be caught. In contrast, as
how large an area needs to be quarantined no host fruit, the females will need to move rainfall increased, fewer males were caught.
and treated to eradicate it. away to find somewhere to lay their eggs,” Weldon says that they don’t yet fully
From 2015 to 2017, Weldon led a research explains Weldon. understand these behaviours, but are
project on the dispersal of Oriental fruit Interestingly, the researchers also found looking into them. The first step was
flies, studying how far they can fly in that females would not move away from studying dispersal patterns, while further
relation to physiological and environmental host plants even when these were not in research will examine the underlying causes.
variables. Fly maturity and sex, and the fruit. There is still some uncertainty about “Most control tactics require a really good
availability of host fruit were studied what causes this behaviour, says Weldon. understanding of the biology of the insect.
as relevant physiological factors, while “Perhaps the females were using some That is where going into the detail comes
environmental factors included temperature information from the tree other than host into play,” stresses Weldon. “If you want to
and rainfall. Flies marked with fluorescent fruit to decide whether to stay put, or keep the flies out of the Western Cape, then
pigments were released and recaptured perhaps it relates to the environment that you need to know what determines how far The Oriental fruit fly
weekly for four weeks, providing valuable those particular trees provide.” they fly.” Bactrocera dorsalis.
information on flight distances and drivers.
Sex and age
South Africa has
The results showed that younger males cover
greater distances than older males. Young favourable environmental
males tend to disperse to find unrelated
females for mating, so as to spread their genes. conditions for Oriental
fruit flies to disperse
This behaviour is also seen in other species of
the same genus as the Oriental fruit fly.
20 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 21FQ poSt-HARvESt
Internal browning
Diffu
What have we s ef
br
ow
ni
learnt over the n
gf
past ten years?
af
fe
cts
By Anna Mouton
in Cripps Pink
fth
e fc o
internal
rt e xf w hil eft he f
Diffuse browning Best practices for storage
browning is can develop as early The stage at which you harvest is critical
a post-harvest disorder in which the flesh of as three months into and fruit that has passed optimal maturity
apples turns brown while remaining firm. the storage period. is likely to develop internal browning. “The
vas
The two main types are diffuse browning Fruit that is left longer bulk of your fruit will have to be sold before
u lac
and radial browning. These can occur in on a tree so that it can six months,” states Crouch. “If you want to
r
ed.
f ti
ct
ss
combination — this condition is creatively colour — typically those on ffe risk storing fruit, which fruit are you
ue
a
un
fis
fu f
called combination browning. the inside of the canopy — has fis going to choose for that?” She
na
ex
ffec
te d.
Internal browning is among the most a greater risk of browning and Crouch advises growers to measure
rt
fc o
important causes of losses during the doesn’t recommend storing these fruit for starch breakdown to
he
l eft
post-harvest period, according to Dr Elke more than three months. inform their decision.
scularftissuefw hi
Crouch, a post-harvest physiologist with Step-down cooling
the Department of Horticultural Sciences at Radial browning: a seasonal problem has been effective
Stellenbosch University. But, she says, it’s Radial browning seems most common in reducing the
very important to distinguish which type of when fruit are exposed to cool weather occurrence of diffuse
browning affects your fruit. during the cell enlargement phase. This browning. New
efv a
may lead to denser fruit which could slow research confirms
th
Diffuse browning: all about maturity
t sf
the escape of carbon dioxide — high tissue this and shows that
c
ffe
Diffuse browning is a problem in fruit that carbon dioxide levels are damaging to Com step-down cooling is also
fa
b in ng
was harvested at post-optimal maturity cells. Maturity may also impact at ni essential for the control of
io
nf ow
—characterised by starch breakdown of gas exchange but is not a b
r
alf b radial browning. Crouch thinks that
Radi
ro
40%–50% or greater. Preharvest factors that determinant of radial newer cultivars may be more sensitive to
w
ni
speed up ripening increase the risk of diffuse browning to the same chilling injuries. “All the new protocols have
ng
faff
browning because fruit are more likely to extent as it is for very long step-down cooling,” she observes,
e c ts
be harvested when beyond their optimal diffuse browning. “not like the instant we used to have.”
f b ot hft h efc o rt
maturity. “If you see your orchard is moving Tree age and soil Internal browning in Cripps Pink is well-
fast, the chances of that orchard storing well type do not affect understood, according to Crouch. “We know
are not good,” cautions Crouch. the occurrence of that if you harvest them over-mature and
Preharvest factors that are associated with radial browning. store them at really low temperatures you
e xf
a greater risk of diffuse browning include Radial browning was will get diffuse browning,” she summarises.
nd a
younger trees and orchards on sandy soils. thought to develop early “We know that in some seasons we get
th f
Crop load also plays a role in that larger fruit in storage and packhouses radial browning and in some seasons we
ef
va
sc
ripen faster and store less well. use hyperspectral sorting arf
ul don’t and generally the cooler seasons your
ti ss
Crouch explains the tension between to eliminate brown fruit prior to u e. risk might be higher.”
optimal maturity and colour development. shipping. “But you risk that fruit goes brown Browning in other cultivars is not always
Ian CrouCh | ExpErICo
Better colour translates into higher value — on the water,” says Crouch. Her team’s data as simple. “In other cultivars, like Fuji,
but better storability enables growers to sell showed that radial browning can become we’re still trying to figure all the browning
at a more favourable price. “People want to worse during shipping and shelf life. This is patterns out,” says Crouch. “One needs
store long-term and they want red fruit. Not especially true for high-risk seasons and after research to make a storage recipe for each
all fruit will be able to make that grade.” prolonged storage. specific fruit and each type of browning.”
22 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 23pink
FQ POST-HARVEST
Ke e p yo u r
apples in the “Diffuse browning is managed by having
the right harvest maturity,” says Crouch.
from 2017 to 2019. The apples were “If you harvest anything after 40%–50% was better — step-down cooling is a definite
evaluated for maturity using a range of starch breakdown, that’s high risk and you must,” emphasises Crouch.
measurements including firmness, colour, shouldn’t store longer than four months.”
total acidity, total soluble solids, and starch This can be difficult in practice especially in Step down the browning
breakdown. The aim was to harvest at trees with a large canopy. Results so far suggest that the best protocol
optimum maturity which is characterised by “One should harvest the inside and for step-down cooling starts at 3°C for 30
starch breakdown of 30%–40%. outside fruit separately, because we know days, followed by 2°C for 30 days, followed
Apples were harvested in April and kept their starch breakdown levels are completely by 1°C for the remainder of storage. Crouch
By Anna Mouton Strategies to in controlled atmosphere storage. Five different,” says Crouch. “Unfortunately the points out that any step-down cooling
mitigate the risk of treatments were used — see table below. fruit that hangs longest is also the ripest.” treatment is better than taking fruit directly
internal browning Fruit were then subjected to a simulated Crouch recommends measuring starch to 1°C.
“Internal browning touches
people’s pockets,” says Dr Elke Crouch, a post-
shipping period under regular atmosphere
for six weeks followed by a ten-day shelf life.
“The first season we stored for about
nine months and we didn’t get any internal
breakdown in apples from the inside of the
canopy to avert long-term storage of fruit
with starch breakdown of greater than 50%.
Radial browning is highly seasonal
All the apples undergoing step-down
cooling as well as one group stored
directly at 1°C were treated with 1-MCP
— 1-methylcyclopropene (marketed as
harvest physiologist with the Department browning,” says Crouch. “This season we because it is strongly influenced by pre- SmartFresh) — within seven days of
of Horticultural Sciences at Stellenbosch realised, if you have a high-risk browning harvest factors. Radial browning is more storage. The application of 1-MCP to
University. “Particularly in Cripps Pink, because year, no matter what you do, don’t push common in years with lower temperatures maintain fruit quality is a standard industry
it’s a high value crop.” Crouch is part of a group it.” Stored fruit showed a high prevalence during the period in spring when fruit practice. A control group was stored directly
investigating the impact of harvest maturity of internal browning and superficial undergo early cell division and expansion. at 1°C and not treated with 1-MCP.
and storage conditions on internal browning in scald leading Crouch to caution against Harvest maturity is not a predictor of Both groups stored at 1°C had high levels
Cripps Pink apples. The team is led by Heleen attempting to store Cripps Pink apples for radial browning. Crouch notes that their most of internal browning. Treatment with 1-MCP
Bergman from ExperiCo. as long as nine months. recent data indicated that fruit harvested reduced diffuse browning — as expected.
The researchers sampled apples from five early were more susceptible to radial Diffuse browning is related to increased
farms each in Ceres and Grabouw. They Don’t store up trouble browning than fruit harvested later. More maturity and 1-MCP retards maturity.
collected fruit during three harvest seasons Apples can suffer from diffuse browning, radial research is needed to clarify the relationship. This research was conducted by a team
browning, or a combination of these. Diffuse The risk of both radial and diffuse from the Department of Horticultural
browning has historically been more common browning is reduced by using step-down Sciences at the University of Stellenbosch
in South Africa — but radial browning caused cooling. “The message here is, don’t store in collaboration with ExperiCo. The work is
significant losses last season. at a single temperature of 1°C. When we funded by Hortgro.
did the long-term step-down cooling, the
firmness was better, the quality of the fruit
Storage temperature
Initial 1-MCP
Treatment January end
application 0‒30 days 31‒60 days 61‒90 days September
of trial
1 + 4°
C 3°
C 2°
C 1°
C 1°
C
2 + 3°
C 2°
C 1°
C 1°
C 1°
C
3 + 0‒14 days 2°
C 15‒30 days 1°
C 31+ days 0.5°
C 1°
C 1°
C
4 + 1°
C 1°
C 1°
C 1°
C 1°
C
5 - 1°
C 1°
C 1°
C 1°
C 1°
C
Five different storage protocols were tested. Treatment 2 delivered the fewest defects and most consistent results.
24 FQ ISSUE 08 MARCH 2020 ISSUE 08 MARCH 2020 FQ 25You can also read
