Apple Best Practice Guide

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Clearly there will be continued pressure from consumers to reduce or eliminate the use of post-harvest chemical treatments for apples and other fresh produce. The number of products with label recommendations for use as post-harvest treatments has declined over the last few years. A list of products with current approval is given in Table 8.

 

Table 8.  List of products with label approval for use as a post-harvest dip or drench

Product	Rate (metric) 1000 litres-1	Rate (imperial) 100 gallons-1	Crop
Ethoxyquin	3.7 litres	3 pints	Bramley
Stopit	13.5 litres	10.8 pints	Cox
Calcium Chloride Flake	13.5 kg	13.5 pounds	Cox
Calcium Chloride Liquor	13.3 litres	10.6 pints	Cox
Calcium Metalosate	6.3 litres	5.0 pints	Apples

 

• Before handling or applying a pesticide always read the product label and follow any other guide-lines for use supplied by manufacturers.
• It is essential to follow the instructions on the approved label before handling, storing or using any crop-protection product.

Life cycle

• There are two generations per annum in the UK.
• Larval development has five instar stages.
• The pest overwinters as a second or third instar larva in a silken hibernaculum in crevices in the bark etc.
• There is often considerable winter mortality which is sometimes an important limiting factor in population development.
• After emergence in spring shortly after bud-burst, individual larvae feed amongst the buds, characteristically tying them and the rosette leaves together with webbing.
• On early apple varieties and on pears, larval feeding produces cavities in the receptacle, which later heal to form corky scars characteristic of early caterpillar feeding.
• Larvae pupate when fully fed, normally around blossom time of Cox.
• First generation adult moths emerge in June.
• Eggs are laid in batches on the foliage. These hatch in 7-10 days depending on temperature (see ‘Forecasting’.
• Cool and wet weather conditions at the time of moth flight and/or during egg-hatch limit population increase.
• Many larvae migrate to the growing points in shoots where they form leaf rolls.
• In July and August more mature larvae feed on fruits before pupation in August.
• A second generation of adults occurs in August and September, depositing eggs on leaves and also directly onto fruits.
• These hatch and the young larvae feed beneath silken webs spun on the under-surfaces of leaves, often at a junction between the main and a side vein.
• In late September and October, larvae have reached the second or third instar stage and migrate to crevices in the bark to overwinter.

Pest status

• The summer fruit tortrix moth is an important secondary pest of apple and pear. It attacks foliage and fruit.
• Natural enemies reduce populations in the unsprayed situation.

Other hosts

• Recorded from over 70 species of plant, mainly from the family Rosaceae, including many hedgerow and woodland trees and shrubs.

Varietal susceptibility

• Apple varieties with fruits that are short stalked and/or which hang in clusters, tend to be most susceptible.
• Bramley and Discovery are highly susceptible.

Distribution

Not a native of Britain. First recorded at Teynham in Kent in 1950, for many years it was confined to the South East, especially Kent and Essex.

• More recently it has spread across much of southern and central England where it is now widespread and common.
• It is reputed to be absent from the West Midlands.

Damage

Damage to foliage is unimportant. Damage to fruits occurs at three different times during fruit development:

Overwintered larvae

• Feeding cavities in the receptacle of flowers and young fruitlets later heal to form corky scars characteristic of early caterpillar feeding on mature fruits.

First generation larvae

• Young caterpillars make small, shallow holes in the skin of fruits in July and early August.
• Larger caterpillars graze shallow irregular patches in the skin, especially at the point where fruits are in contact.

Second generation larvae

• Damage is similar to that caused by first generation larvae but occurs in late August and September and appears more freshly formed and may be in progress at harvest.

Recognition

Adult (resting)
Length 8-11 mm, light brown with darker brown markings.

Egg
Flat, oval, light green. Black centre when mature. Laid in scale-like batches on leaves and, for the second generation, sometimes on fruits.

Larvae
Up to 18-20 mm long. Yellow-green, olive green or dark green, usually with a brown head, though head colour is not diagnostic. Spins fine webbing and often occurs in leaf rolls or beneath a leaf tied to fruit.

Other pests with which summer fruit tortrix moth may be confused

Larvae of several leaf-rolling tortrix moths are very similar and are difficult to distinguish from each other.

• Larvae of the fruit tree tortrix moth, Archips podana, occur commonly in orchards in the UK and are particularly difficult to distinguish from those of the summer fruit tortrix moth.

Monitoring

Pheromone traps
The flight activity of male moths should be monitored using sex pheromone traps. The delta design is used widely.

• Traps should be set out in orchards shortly after blossom.
• Each orchard should be individually monitored with a trap.
• The traps should be hung from the branch of a tree at mid canopy height in the centre of the orchard and oriented to allow flow through of the prevailing wind.
• The number of moths should be recorded weekly, and captured moths removed.
• Lures should be changed every 4-6 weeks as recommended by the manufacturer.
• It is important to change them before the second generation.
• Sticky bases should be changed if their effectiveness declines.
• The threshold for determining whether the pest is a problem in an orchard is 30 moths per trap per week.
• However, temperature sums to predict egg hatch to determine correct timing of egg hatch sprays should be started from the date when the catch exceeds 5 moths per trap (see ‘Forecasting’ ).

Shoot damage

• During the first half of July, leaves tied by spinning larvae are easily recognisable on the top of the shoots.
• If shoot damage exceeds 5-8%, a curative treatment should be applied immediately or postponed to the beginning of egg-hatch of the second generation.

Fruit damage

• Inspecting fruits for damage, either whilst developing on the tree, at harvest or during grading (remembering that badly damaged fruit may have been discarded at harvest), indicates if populations have been high and whether treatment is likely to be required for the next generation or the next season.

Trunk banding

• Trunk bands can be set on a sample number of trees in early September and the number of overwintering larvae counted during the dormant period.

Chemical control

Various insecticides that are approved for control of colding moth, totrix moths or for general caterpillar control are likely to control summer fruit tortrix moth.

• Summer fruit tortrix moth may be controlled with  indoxacarb (Steward or Explicit), spinosad (Tracer), or with the biocontrol agent Bacillus thuringiensis, applied to coincide with egg hatch, usually in June.
• Chlorantraniliprole (Coragen) is also thought to offer incidental control when applied against codling moth.
• Pyriproxyfen (Harpun) may also offer incidental control of summer fruit tortrix moth when applied for codling moth control. It inhbits egg hatch, metamorphosis of nymphs to adtuls and reduces the fecundity of adult females. However, as a new product to the UK in 2020, further experience is required to inform growers and agronomists of its efficacy at controlling summer fruit tortrix moth.
• Bacillus thuringiensis is considered to be of only moderate efficacy.
• The summer fruit tortrix ganulovirus (Capex) is another option. Highly specific to summer fruit tortrix, it is ideal for use in organic and IPM production systems and has no harvest interval or buffer zone requirement. See information on viruses in biological control section below.
• The first spray should be applied at the onset of egg hatch of the first generation.  Further sprays should be applied at 7-10 day intervals until the egg hatch period has ended.
• Synthetic pyrethroids are highly effective but their use should be avoided as they are harmful to predatory mites and other beneficial insects.
• A pre-blossom spray of indoxacarb (Steward or Explicit) or methoxyfenozide (Runner), often applied to control early season caterpillars, will reduce populations of overwintered summer fruit tortrix moth caterpillars, but is unlikely to be sufficiently effective to prevent damaging first and second generations developing subsequently.
• The onset of egg laying is taken as the date when the pheromone trap catch exceeds 5 moths/trap/week.
• If traps are only examined weekly, the date when this occurred can often be pin-pointed more accurately by examination of daily temperature records.
• The moths fly when dusk temperatures exceed 15 °C.
• The onset of the egg hatching period occurs 7-21 days later, depending on temperature. It can be calculated accurately from daily maximum and minimum air temperatures using the look-up table (see ‘Forecasting’ ).
• The daily percentage egg development amounts are summed from the date of the onset of egg laying. When the sum reaches 90%, egg hatch is imminent and the first spray should be applied.
• A second generation occurs in August and September which can be damaging on later harvested varieties. The second generation may be controlled in the same way.

Sex pheromone control

There are three basic methods by which a pest’s sex pheromone can be exploited for control:

• Mating disruption where the pheromone is used alone to interfere with the normal attraction of males to females by providing false trails and/or sensory overload
• Mass trapping where the sex pheromone is used to attract males to a trap where they are captured and killed physically
• Attract and kill where the sex pheromone attracts males to a device or place where they come into contact with an insecticide

The RAK 3+4 mating disruption system

RAK 3+4 is a combined pheromone control system which reduces fruit damage from codling moth (RAK 3) and summer fruit tortrix (RAK 4). Both pheromones disrupt mating behaviour and therefore prevent populations from developing. The pheromones are released from sealed chambers by volatilisation, preventing male and female moths from locating each other and reproducing.

• RAK 3+4 is most effective in orchards with a low pest population density. It should not be used in orchards where more than 1% of fruits (including fallen fruits) were damaged by codling and tortrix moths in the preceding year, unless the first generation of moths is treated with a control product to reduce initial populations.
• Best results are achieved in isolated orchards, i.e. those which are 100 m or more away from other orchards or high trees.
• Optimum results are also achieved in grouped orchards containing trees of similar size and shape.
• RAK 3+4 will not be effective if there is a high density of codling moth and/or tortrix moth in the area adjacent to the orchard being treated. It will not be effective in orchards less than 1 ha in area.

Timing of application and dose rate

• The pest population should be monitored using an appropriate pest forecasting system or monitoring traps and the product should be put in place one week before the forecast arrival of the adult moths.
• The latest time of application is when the first generation of adult moths start to fly. Only one application of product per season is required.
• The product is packaged in airtight bags and protected from the light. The package should therefore only be opened immediately prior to installation to avoid any loss of efficacy.
• RAK 3+4 should be used at a rate of 500 product units per ha. The density should be increased at the orachrd border – see below.

Positioning the dispensers

• The pheromone must be distributed evenly throughout the orchard in a grid system at 500 product units per hectare. One should be placed approximately every 20 square metres, e.g. for a row width of 3.5 m a unit should be placed every 5.7 m.
• It is important to make sure that they are positioned in the shade or in places which will be in the shade by the end of vegeative growth.
• The product must be placed in the upper third of the trees, preferably at alternating heights.
• The manufacturer provides further guidance on using additional pheromone around the orchard borders to prevent moths from encroaching into the treated orchard from adjacent areas.
• Further guidance is provided on the use of additional pheromone monitoring traps to check on the efficacy of the pheromone on a weekly basis.

Pheromone attract and kill:
The sex pheromone is incorporated into a material together with an insecticide (usually a synthetic pyrethroid).

• Blobs of the material are extruded onto the trunk and branches of trees throughout the orchard (typically 1-2 blobs per tree) at the start of moth flight, as indicated by pheromone traps.
• The males attempt to mate with the blobs, picking up a dose of insecticide in the process.
• The technique is effective and uses a fraction of the amount of insecticide used in an insecticide spray treatment.
• However, no product is approved for use in the UK currently.

Insecticide resistance

Strains of summer fruit tortrix moth, that are less susceptible to conventional insecticides  than strains that occur in unsprayed orchards, have been shown to occur in the UK.  However, the reduction in susceptibility is small.

Forecasting

The rate of development of each of the developmental stages of summer fruit tortrix moth is only completed when a specific heat sum has accumulated. The specific heat sums are known and can be calculated each day from the daily maximum and minimum air temperature. The forecasting model PESTMAN can be used to give approximate predictions of the timing of occurrence of each of the life stages of the pest.

Forecasting the time that overwintered caterpillars reach the last instar stage (for timing Insegar sprays)

• Overwintered larvae reach the last instar development stage approximately 75‑100 day-degrees C above a threshold temperature of 8^oC starting from 1 January.

Forecasting the start and peak of first generation adults

• The start and peak of the flight of first generation adult moths occurs approximately 170 and 210 day-degrees C above a threshold temperature of 10^oC after 1 January.

Forecasting the start and peak of second generation adults

• The start and peak of the flight of second generation adult moths occurs approximately 616 and 693 day-degrees C above a threshold temperature of 10^oC after 1 January.

Forecasting the timing of egg hatch

• Egg development takes approximately 103 day-degrees C above a threshold temperature of 8.6^oC.
• The percentage egg development that accrues at various daily maximum and minimum air temperatures is given in the look-up table.
• Sum the daily percentage egg development amounts starting from the day the first pheromone trap catch of 5 or more moths occurred.
• Apply the first egg hatch spray when the temperature sum reaches 90-100%.
• If above threshold catches continue for more than one further week, a second spray may be necessary 7-10 days later.

Cultural control

Trees which have a dense canopy and vigorous shoot growth tend to support greater populations of caterpillars. If shoot growth then ceases when caterpillars are young, due to water stress and/or a heavy fruit load, the caterpillars tend to move to feed on fruits, especially those in clusters, and damage intensifies.

• Avoiding this situation by tree management reduces losses.
• The cultural control approaches recommended for codling moth are likely also to be effective in controlling summer fruit tortrix moth, though hygiene measures need to be modified to suit this particular species.
• Furnishing the trees with artificial refuges for earwigs and other insect predators is likely to help reduce young caterpillar populations.
• Ideally, a refuge should be provided in each tree. This may simply be some extra lengths of hollow tree tie round the stake.
• In orchards with high tree densities, it is likely to be impractical to provide more elaborate refuges such as half of a plastic drinks bottle containing a roll of corrugated cardboard.

Natural enemies

Insectivorous birds

• Tits especially pick overwintering larvae from bark crevices, but do not forage specifically for the pest unless population densities are very high and for this reason are of limited value only.

Egg parasites

• The egg parasitic wasp Trichogramma can be introduced (4 releases of 2.5 m per ha have been shown to reduce damage by 40-85%) but such introductions are not cost effective.

Larval parasites

• The parasitic wasp Colpoclypeus florus is an external parasite of third to fifth instar summer fruit tortrix moth larvae.
• The parasite can be seen attached behind the head of its host.

Predatory insects

• Earwigs and predatory mirid and anthocorid bugs feed of eggs and young larvae.

Virus diseases

• A nucleopolyhedrovirus (AoNPV) and two strains of a granulovirus (AoGV) of summer fruit tortrix moth are known (see ‘Biological control’ below).
• These are normally found in association with commercial applications of biocontrol agents, though natural infections of AoGV were found in two orchards near Faversham in Kent in 1993.

Biological control

Bacillis thurigiensis

• A programme of weekly sprays of Bacillus thuringiensis (Bt) throughout the egg hatch period gives fairly good control, though control may not be as good as that achieved with conventional or Insect Growth Regulator insecticides (see below).
• Bt has to be ingested to act and is most effective in warm weather when caterpillars are feeding actively.
• The bacterium produces a crystalline toxin. The insect dies from the effects of this toxin rather than from pathogenesis due to the bacterium.
• Bt is of short persistence as it is degraded by heat and UV light.
• It is most effective against newly hatched larvae before they form leaf rolls in which they feed internally and are inaccessible to sprays.
• The first spray should be applied at the onset of egg hatch which should be determined from pheromone trap catches and egg development sums calculated from the daily maximum and minimum air temperature (see ‘Forecasting’ ).
• Bt is not detected by conventional pesticide residue analysis.

Viruses

• Three baculoviruses of summer fruit tortrix moth have been tested for use in the field in Europe including a nucleopolyhedrovirus (AoNPV) and a granulovirus (AoGV).
• AoNPV can control summer fruit tortrix very effectively and is highly host-specific but the virus is uneconomic to produce and is not available commercially.
• AoGV has a very slow pathogenesis. Newly hatched larvae become infected in the first instar development stage and only die when they reach the final development stage.
• They can live longer than uninfected larvae and larval damage to fruit may not decrease in the short term.
• In the longer term, a high degree of control can be obtained. The virus may persist for several generations.
• A commercial formulation is produced in Switzerland but is not registered for use in the UK.

Biotechnological control

Pheromone mating disruption

• Pheromone mating disruption systems have been developed for summer fruit tortrix moth in continental Europe.
• One system uses red spaghetti double tube plastic dispensers, one tube containing the pheromone, the other a metal wire to give rigidity.
• The dispensers are wrapped round the branch of a tree.
• A typical application rate is 1000 dispensers per ha, one application being required per season.
• The system was developed to control summer fruit tortrix moth and other tortrix moths, such as Pandemis heparana and Archips rosana, and uses a common pheromone component (Z11-14:Ac).
• Pheromone mating disruption systems have a number of important limitations.
• They are only effective if populations of the target pest are low initially; they have to be applied over a large area; they are generally costly in comparison with insecticides and they have a high labour requirement for application.
• There are no pheromone mating disruption systems approved for use in the UK.

Further reading

Charmillot, P. –J. & Brunner, J. F. 1989. Summerfruit Tortrix, Adoxophyes orana: Life cycle, warning system and control. Entomologia Hellenica 7, 17-26.

Cross, J. V. 1997. The susceptibility of summer fruit tortrix moth, Adoxophyes orana (Lepidoptera: Tortricidae), to chlorpyrifos and strategies for insecticidal control in orchards. Annals of Applied Biology 131, 197-212.

Van der Geest, L. P. S. & Evenhuis, H. H. (Eds). 1991. Tortricid Pests, Their Biology, Natural Enemies and Control. World Crop Pests, Vol. 5. Elsevier, Amsterdam.

Controlled atmosphere (CA) storage delays ripening and senescence changes in apples and preserves many important quality attributes such as firmness, acidity and soluble solids (sugar) concentration. However, one negative consequence of the use of CA storage for prolonged periods is the reduced production of compounds that contribute to aroma and flavour.  

In order to increase the flavour of Cox apples:

• Harvesting should not be earlier than is necessary to achieve the period of storage that is required.  Delay in harvesting maximises flavour potential, but harvesting too late reduces storage life and has adverse effects on fruit texture.
• Reserve the use of ultra-low oxygen or ULO (1.2% O₂) for medium or long-term storage provided that the firmness of fruit stored short-term is adequate for the requirements of the market.
• Raise the oxygen concentration in ULO stores to 2% O₂ 4-5 weeks prior to opening the store provided that firmness is adequate for the requirements of the market.
• Practices to maximise flavour in stored Cox apples should only be implemented when there is unlikely to be any detrimental effects on other quality parameters. Full knowledge of the condition of the fruit in store is essential in the decision making process which can be achieved by regular store monitoring.  
• The advice provided above on conditioning is likely to be appropriate to all dessert cultivars stored in ULO conditions.

Ethylene gas is produced by apples during the process of ripening either on the tree or during storage. Ethylene, the ‘ripening’ hormone, triggers and co-ordinates many of the ripening changes that occur in stored apples such as softening and aroma development.

Storage under refrigeration and in controlled atmospheres reduces the rate at which these ripening changes take place. More effective control of ripening and a consequent improvement in fruit quality may be expected by further suppression of ethylene production by the fruit.

Ethylene removal is generally only worthwhile with unripe fruit therefore apples need to be harvested pre-climacteric i.e. before ethylene production rate of fruit on the tree increases.

Ideally all fruits should contain less than 0.1 ml l^-1 of ethylene. It is easier to meet these requirements for Bramley than for Cox (or other dessert varieties). With the latter, picking fruit that is too immature may affect adversely its eating quality.

Bramley

The use of an ethylene converter is sufficient to control ethylene production in CA-stored Bramley apples without additional measures to inhibit production of ethylene. This is related to the immature state of the fruit at commercial harvest when compared with Cox and other dessert cultivars rather than an innately low production rate. Additionally the high concentration of CO₂ (5-10%) used for the storage of Bramley suppresses ethylene production.

Beneficial effects of ethylene removal from Bramley stores include delayed development of superficial scald, firmness retention and reduced susceptibility to core flush.

Ethylene scrubbing has no effect on chlorophyll loss (greenness) and does not affect acidity or sugar content of the fruit. There were no adverse effects on fruit quality resulting from the removal of ethylene from commercial stores of Bramley.

However, in other trials ethylene removal increased susceptibility of fruit to external CO₂ injury. Consequently it is important to delay the establishment of CA conditions.

Requirements for effective ethylene scrubbing

• To achieve scald control in Bramley apples, maintain an ethylene concentration of less than 1 ml l^-1 and ideally less than 0.1 ml l^-1in the storage atmosphere for most of the storage period.
• Ethylene removal systems for Bramley should be capable of maintaining 1ml l^-1 of ethylene in the storage atmosphere at an assumed rate of ethylene production of 1ml kg^-1 h^-1.
• Fruit should not be late picked otherwise the ability to control ethylene production will be compromised. This may not be evident from measurements of ethylene concentration in the store atmosphere. Once the rapid phase of ethylene production is underway then removal of ethylene has little effect in slowing down ripening processes.
• The removal of ethylene from the storage atmosphere using heated catalyst scrubbers is an alternative to the use of SmartFresh for controlling superficial scald.
• Growers can achieve control of scald for 6 months by attaching an ethylene scrubber to storage chambers where the carbon dioxide level is maintained at 8‑10% by ventilation with outside air.
• Longer storage without scald development is possible where ethylene scrubbing is combined with low oxygen storage (5% CO₂ + 1%O₂).
• In commercial trials no scald was evident in fruit stored in 5% CO₂ + 1%O₂ with continuous removal of ethylene when the trials were concluded after 10 months.
• Despite the effectiveness of ethylene scrubbing in controlling scald the use of heated catalyst systems may not be justified due to the high capital and running costs.
• Currently there are a number of alternative ethylene removal systems being tested on UK stores. These include low temperature catalyst systems, ozone generators and ethylene absorbents.
• Whilst growers will be interested in comparing the costs of these various ethylene removal technologies it is the ethylene removal efficiency that is of paramount importance.
• There is a need to compare the efficacy of current ethylene control technologies (chemical absorption, destruction by ozone or by a low temperature (photo-induced) catalyst) to enable growers to adopt the most appropriate method for their particular situation.

 

Cox’s Orange Pippin

Early harvesting plus effective ethylene removal can only achieve a delay in the onset of rapid production of ethylene but this can produce worthwhile benefits in the quality of fruit from store.  However ethylene scrubbing without additional treatments to inhibit ethylene production will not slow the rate of softening during storage.

Inhibition of ethylene can be achieved by subjecting fruit to 15% CO₂ for 15 days prior to CA storage although this was found to induce the development of low temperature breakdown in the fruit late in the storage period. Subsequently 5% CO₂ for 15 days was found to reduce the risk of storage problems without affecting the beneficial response to ethylene removal.

The main benefit of ethylene scrubbing of Cox stores is reduced softening of the fruit although greater retention of acidity is also likely. There have been no effects of ethylene removal on the change in background colour.

• Although there are major quality benefits that can be achieved in Cox apples by removing the ethylene for CA stores the effects are inconsistent from year to year and between consignments.
• Ethylene production in Cox apples is higher than in Bramleys due to the fact that they are harvested closer to the point of ripening (initiation of rapid ethylene production) on the tree.
• For Cox stores the size of scrubber that is required and consequently the investment and running costs are increased by a factor of about 4 when compared to Bramley stores.
• Additional ‘conditioning’ techniques are required to reduce ethylene production in order to make ethylene removal effective which adds to the complexity of managing the crop during the early period of storage.
• Some ‘conditioning’ treatments such as pre-treatment with high levels of carbon dioxide may have deleterious effects on the fruit late in the storage period.
• Further developments in ethylene removal technology may improve the efficacy or cost-effectiveness of ethylene removal for Cox and may make it viable commercially

 

Gala

Most of the work on ethylene removal at East Malling was done on Cox and Bramley apples. There are recent reports from Brazil that removal of ethylene from CA stores (3% CO₂, 1% O₂ at 1^oC) containing Gala apples improves the firmness of fruits stored for up to 8.5 months. Low ethylene also maintained the appearance, background colour, crispness, juiciness and taste of stored fruit.

Strategies that offer the prospect of improved control of ethylene production in apples include:

• Conventional breeding techniques – selection of genotypes with low production rates.
• Biotechnology – control of expression of regulatory proteins (ACC synthase and ACC oxidase) by genetic modification.
• Inhibition of regulatory proteins using pre-harvest bioregulants such as AVG (active ingredient of the commercial product ReTain^R marketed by Valent BioSciences Corporation).
• Blocking the effects of ethylene using post-harvest bioregulants such as 1-MCP (active ingredient of SmartFresh ^SM marketed by AgroFresh Inc.
• Inhibition of ‘feed-back’ effect using ethylene removal. Apples and other climacteric fruits are responsive to accumulating levels of ethylene. Effective removal of ethylene from the storage environment can delay the rise in ethylene production in stored apples.

Conventional breeding techniques

This strategy is essentially for the longer term and is not relevant to the improvement of existing commercial cultivars.

Biotechnology

This strategy has been demonstrated to be effective on the cultivar Greensleeves. Transformed clones grown in glasshouses at East Malling were found to have markedly lower ethylene production rates than untransformed control trees. However, further work is required to transform cultivars that are important commercially in the UK and to restrict altered gene expression to the fruit only. There are important issues to be resolved as regards public perception and acceptance of this technology.

Pre-harvest bioregulants

This strategy presents an opportunity for the control of ethylene based on chemical inhibition. Earlier trials (1997-2006) carried out with ReTain^R as a pre-harvest spray to delay the onset of ethylene production and to delay the harvest window for long-term storage.  While ReTain^R was never registered in Europe, it is used in North and South America, New Zealand and South Africa.

Advances in formulation of 1-MCP has led to the development of Harvista^TM for pre-harvest sray application for apples as a single spray or split application to extend the harvest window for up to several weeks. It is currently undergoing the process of registration in the EU.

Post-harvest bioregulants

SmartFresh^TM, a commercial formulation of the potent ethylene inhibitor 1-MCP, has been used increasingly by UK growers since the product was registered for use in 2003. Efficacy of the product was tested extensively at EMR from 2000 to 2003 and there is now considerable commercial experience of using the product.

Other formulations of 1-MCP are being developed commercially in the USA and include  FYSIUM^TM (PACE). Recent developments with 1-MCP have seen the active ingredient incorporated into packaging and as slow release sachets (Fruitbrite^TM) that can be added to cartons of fruit during the supply chain. These are not currently available for use in the EU.

Ethylene removal

This strategy can provide commercially important benefits to CA-stored apples although there are concerns that the technique may not provide consistent improvement and that scrubbing systems currently available may not be cost effective.

Prior to the advent of 1-MCP the possible use of ethylene scrubbing technologies had a greater significance. Whilst both these technologies are intended to maintain a low rate of ethylene production by the fruit in the case of 1-MCP the fruit is insensitive to ambient ethylene for a significant period after treatment whereas with ethylene scrubbing fruits remain sensitive to ethylene at all times.

More recently, a range of ethylene scrubbing devices based on ozone or cold-plasma have been or are in the process of being commercialised. Some of these claim to have dual activity, both in terms of destroying ethylene and surface sterilising or scrubbing out air-borne pathogens. The capacity of the scrubber to remove the high evolution rates of ethylene from apples needs to be considered before adopting any particular technology. Other scrubbing technologies based on ambient temperature catalytic removal using palladium based catalysts and absorbers have been used to reduce ethylene in consumer packs in the retail chain.

The physiology of flower and fruitlet drop in apples

The natural abscission (drop) of flowers and fruits

Fruitlets were traditionally thought to drop off in response to the death of their seeds (embryos) and the cessation of the supply of auxins from the live seeds across the abscission zone in the fruit stalk.

• Although embryo death possibly explains a significant proportion of natural fruitlet abscission, [hyperlink 18] it does not explain it all.
• Fallen fruitlets can often be found which have live plump seeds within them.
• Also, research has failed to explain conclusively the causes of the embryo abortion itself.

Hormones occurring naturally within the tree that are associated with flower and fruitlet abscission

• Several natural plant hormones [hyperlink 19] have been implicated in the tree processes leading to flower and/or fruitlet abscission (drop), particularly auxins and ethylene.

Application of plant growth regulators to induce flower and fruitlet abscission

• Various chemicals [hyperlink 20] have been shown to have thinning action when sprayed onto apple trees including, auxins, carbaryl, ethylene releasing chemicals, photosynthesis inhibiting chemicals and cytokinins (benzyl adenine – BA).
• Recent studies have shown that jasmonic acid and n-propyl dihydrojasmonate (PDJ) may have potential as a fruitlet thinner in certain fruit crops (Fujisawa et al., 1997) see Further reading [hyperlink]).

Apples supplied to the market need to be free from internal or external disorders and should have limited potential to develop disorders during the period from retailing to consumption. Growers need to recognise early symptoms of disorders during the monitoring of their stores and to determine the likely progression by examining after a simulated marketing period.

Proper diagnosis of disorders is important in order to take remedial action in the future thereby preventing a recurrence of the problem. Images of the disorders of the flesh and of the skin, described elswhere in this Guide were also included in a wall chart (‘Apple Storage Rots and Disorders’) produced by the HDC and distributed to all registered growers in 2005.

 

Classification of disorders

Symptom expression varies according to variety and storage conditions but in most cases it is possible to make an accurate diagnosis on the basis of the photographs provided in this section.  The disorders have been grouped arbitrarily into those that are visible externally and those that are visible on cutting the fruit. It is accepted that some disorders could be placed in either category e.g. water core develops internally but in some cases, particularly in Bramley apples, the disorder is visible externally.

Within each of the two main categories three further categories of disorders are recognised. Firstly, those that occur as a normal consequence of storage; secondly those induced by the storage conditions and usually due to incorrect concentrations of carbon dioxide and/or oxygen and thirdly, disorders associated with mineral deficiencies in the fruit at harvest (internal only).

It is recognised that some disorders could be placed in more than one category e.g. bitter pit and related disorders occur naturally during storage but are induced by mineral deficiencies in the fruit at harvest. Despite this the following classification should be helpful to growers to recognise the disorders and determine the likely cause. The list is not fully comprehensive. Disorders that do not generally affect the more important commercial cultivars in the UK have been omitted.

 

% Starch (blue-black)	Starch score (Streif chart)
100	1
78-99	2
70-77	3
58-69	4
40-57	5
28-39	6
18-27	7
8-17	8
3-7	9
0-2	10

 

The Ctifl chart is particularly useful for estimating starch patterns. The chart shown here is for cultivars that show a progressive clearance of starch from the centre of the apple.

 A second chart is available (not shown) for cultivars that lose starch progressively from all regions of the flesh (radial type). An approximate conversion of score to % black is as follows: 1-100%, 2-94%, 3-88%, 4-82%, 5-73%, 6-69%, 7-63%, 8-47%, 9-33%, 10-13%.

The summer fruit tortrix moth is an important secondary pest of apples and pears, especially in eastern and south-eastern England. The life cycle involves two generations a year in the UK.

Short stalked varieties such as Bramley and Discovery are most susceptible, but all varieties of apple and pear may be attacked.

Damage to foliage is unimportant but damage to fruits occurs at three different times during fruit development.

Larvae of several leaf-rolling tortrix moths are very similar and are difficult to distinguish  from each other. The pest should be monitored with pheromone traps weekly from petal fall of apple to the end of August.

The need to treat for the pest should be determined by high trap catches (>30 moths per trap per week) or damage the previous season, or by the presence of high populations of caterpillars in blossom trusses in spring before bloom.

Control  

Various insecticides that are approved for control of colding moth, totrix moths or for general caterpillar control are likely to control summer fruit tortrix moth.

• The pest may be controlled with indoxacarb (Steward or Explicit), spinosad (Tracer) or with Bacillus thuringiensis (Dipel DF), applied to coincide with egg hatch usually in June.
• Bacillus thuringiensis is considered to be of only moderate efficacy. The first spray should be applied at the onset of egg hatch of the first generation.  Further sprays should be applied at 7-10 day intervals until the egg hatch period has ended.
• Synthetic pyrethroids are highly effective but their use should be avoided as they are harmful to predatory mites and other beneficial insects.
• Chlorantraniliprole (Coragen) is also thought to offer incidental control when applied against codling moth.
• Pyriproxyfen (Harpun) may also offer incidental control of summer fruit tortrix moth when applied for codling moth control. It inhibits egg hatch, metamorphosis of nymphs to adults and reduces the fecundity of adult females. However, as a new product to the UK in 2020, further experience is required to inform growers and agronomists of its efficacy at controlling summer fruit tortrix.
• The summer fruit tortrix ganulovirus (Capex) is another option. Highly specific to summer fruit tortrix, it is ideal for use in organic and IPM production systems and has no harvest interval or buffer zone requirement.
• The onset of egg laying is taken as the date when the pheromone trap catch exceeds 5 moths/trap/week. If traps are only examined weekly, the date when this occurred can often be pin-pointed more accurately by examination of daily temperature records.
• The moths fly when dusk temperatures exceed 15 °C. The onset of the egg hatching period occurs 7-21 days later, depending on temperature. It can be accurately forecast from daily maximum and minimum air temperatures using the look-up table provided.
• The daily percentage egg development amounts are summed from the date of the onset of egg laying. When the sum reaches 90%, egg hatch is imminent and the first spray should be applied.
• A second generation occurs in August and September which can be damaging on later harvested varieties. The second generation may be controlled in the same way.

Sex pheromone mating disruption  

RAK 3+4 is a combined pheromone control system which reduces fruit damage from codling moth (RAK 3) and summer fruit tortrix (RAK 4). Both pheromones disrupt mating behaviour and therefore prevent populations from developing. The pheromones are released from sealed chambers by volatilisation, preventing male and female moths from locating each other and reproducing.

• RAK 3+4 is most effective in orchards with a low pest population density. It should not be used in orchards where more than 1% of fruits (including fallen fruits) were damaged by codling and tortrix moths in the preceding year, unless the first generation of moths is treated with a control product to reduce initial populations.
• In AHDB Project TF 223 (Improving integrated pest and disease management in tree fruit), RAK 3+4 provided similar control of codling, fruit tree tortrix and summer fruit tortrix moths when compared to conventional spray programmes in field trials. It did not provide complete control and it may be necessary to employ additional sprays should monitoring trap catches of moth pests exceed damage thresholds, especially in early ripening apples and pears, which are more vulnerable.
• Best results are achieved in isolated orchards, i.e. those which are 100 m or more away from other orchards or high trees.
• Optimum results are also achieved in grouped orchards containing trees of similar size and shape.
• RAK 3+4 will not be effective if there is a high density of codling moth and/or tortrix moth in the area adjacent to the orchard being treated. It will not be effective in orchards less than 1 ha in area.
• RAK 3+4 is specific to codling and tortrix moths. Other moth pests such as Blastobasis lacticollela can increase in population where other lepidoptera control agents are not being used.
• Further details on time of application, dose and positioning of dispensers.

Insecticides approved on apple for control of codling, tortrix moths or caterpillars on apple which are likely to control summer fruit tortrix moth or offer incidental control when applied to control other pests

Choice of insecticides – efficacy factors

Active ingredient

Trade name (examples)

Class1

Selectivity

Label rec’s2

Safety to Typhs

Suggested intervalbetweensprays(days)

adoxophyes orana granulovirus

Capex

microbial biocontrol

highly selective

sft

safe

u

Bacillus thuringiensis var. kurstaki

Dipel DF

bacterialinsecticide

selective to caterpillars

c

safe

7

chlorantraniliprole

Coragen

anthranilic diamide

selective

c

safe

14

deltamethrin

Decis Forte etc.

pyrethroid

broad spectrum

cm, t

harmful

none stipulated

E8, E10-dodecadienol, Z11-tetradecenylacteate, n-tetradecylacetate

RAK 3+4

sex pheromone mating disruption

highly selective

cm, sft

safe

none stipulated

indoxacarb

Steward, Explicit

oxadiazine

selective

c, cm, ftt, sft, wm

u

varies with product

pyriproxyfen

Harpun

metamorphosis inhibitor

selective

cm

safe

none stipulated

spinosad

Tracer

neural blocker

selective

C, cm, ftt,sft

safe

u

Choice of insecticides – Safety factor Read and and follow the label before applying any sprays

Hazards2

Harvest interval(days)

Max. no. sprays

Buffer zoneWidth (m)

Anticholin-esterase?

Humans

Fish & aquatic life

Bees

adoxophyes orana granulovirus

no

u

u

u

0

u

0

Bacillus thuringiensis

no

u

u

u

Varies with product

Varies with product

5

chlorantraniliprole

no

h

ed

h

14

2

10

deltamethrin

no

h, i

ed

d

7

u

50

E8, E10-dodecadienol, Z11-tetradecenylacteate, n-tetradecylacetate

no

u

t

u

None stipulated

1

u

indoxacarb

no

h

ed

u

7

3

15

pyriproxyfen

no

d

t

u

fruit diameter up to 40mm

2

20

spinosad

no

u

ed

h

7

4

40

Keys:    1CSI=chitin synthesis inhibitor, JHA=juvenile hormone analogue2c=caterpillars, cm=codling moth, ftt=fruit tree tortrix, sft=summer fruit tortrix,  t=tortrix, wm=winter moth 3d=dangerous, ed=extremely dangerous, h=harmful, i=irritant,  t=toxic, u=no hazard specified

 

Control in organic orchards

Summer fruit tortrix moth should be less problematic in organic orchards because populations are regulated by natural enemies, especially parasitic wasps and probably also because tree vigour is lower in organic orchards (see ‘Cultural control’).

• If control measures are necessary, sprays of Bacillus thuringiensis or spinosad (Tracer), should be applied in the same way as in conventional orchards (see above).
• In addition, the granulovirus (Capex) that is available to control summer fruit tortrix is highly specific to this pest. It is ingested by larval feeding. The larvae subsequently die and break down. Capex is ideal for use in organic and IPM systems of production. Approval should always be sought from organic certification bodies before use in organic production systems.

 

 Further reading