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Storage rots

Introduction

Fungal rots are responsible for significant losses in stored apple in most seasons.  They can be divided into two broad groups:

  • Those causing rots primarily after harvest (store diseases)
  • Those that also cause rots in the orchard (orchard diseases). 

Rotting in store due to the latter group mainly results from fruit infection that occurred before harvest, but remained symptomless and subsequently developed in store.  The store diseases are usually wound rots which gain entry to damaged fruit at harvest. 

Cox is most susceptible to rotting.  Losses in other varieties such as Bramley, Braeburn, Gala or Jonagold are usually much lower, but occasionally certain fungi e.g. Phytophthora syringae, can cause significant losses in these varieties. Orchards differ considerably in actual losses due to rots and the main fungi responsible. 

Information on losses in store and the rots responsible for an orchard is important if losses are to be minimised and the appropriate control measures applied.  This information can be obtained from assessment of rots in the packhouse during grading.

Factors affecting fruit susceptibility to rotting

Fruit maturity:  correct harvest date is important as overmature fruit are more prone to damage and rotting.

Handling:  poor handling of fruit at harvest increases the risk of wound fungi such as Botrytis, Penicillium and Mucor.

Mineral composition:  fruit low in calcium and high in potassium and nitrogen are more prone to rots particularly Gloeosporium in Cox.  Therefore, correct mineral composition is important for varieties such as Cox and Bramley.

Weather:  rainfall is the most critical factor in determining infection of apples by fungi.  Wet summers and harvests usually result in high rot incidence in store.

Storage rots (orchard diseases)

Disease

Varieties

Source

Entry

Weather factors

Cultural control

Fungicides

 

Brown rot (Monilinia fructigena)

 

All varieties

Cankers, mummified fruit on orchard floor and tree

Initially by wounds.  Spread by contact

Warm summer + rain

Prune out cankers

Remove/collect mummies

Good control of P&D

Avoid fruit damage

Close supervision of pickers to ensure no damaged fruit is stored

 

Pre-harvest spray depending on risk

 

Black rot

(Botryosphaeria obtusa)

See images below

 

Cox

Fiesta

+ others

Cankers, mummified fruit, dead twigs, prunings, weeds

Direct and wounds

Warm (20ºC) + rain, humid

Prune out cankers and dead wood

Remove/collect mummies

Avoid piles of prunings in orchard

 

At present not important enough to require special measures

Gloeosporium rot

(Gloeosporium spp)

 

Cox, Gala

Jonagold

Egremont Russet

Cankers, pruning snags, mummified fruits

Direct, through lenticels, eye, stalk, russet cracks

Warm weather + rain

Prune out cankers, dead stubs and die-backs

Remove mummies

 

Pre-harvest sprays July-September

 

Phytophthora rot

(Phytophthora syringae)

 

All varieties

Soil splash

Direct entry, spread by contact

Wet especially near picking

Maximum width grass strip

Mulching to cover soil to reduce soil splash

Removing low hanging branches

Selective picking

Not muddying bulk bins

Encouraging earthworms to             remove leaf litter

Post-harvest urea to trees to encourage leaf rot when fall

Pre-harvest sprays

 

 

Botryosphaeria rot on apple fruit in orchard showing characteristic concentric zones of rot growth

 

 

 

 

 

Botryosphaeria rot around calyx end of Cox apple, associated with insect damage

 

 

 

 

 

 

 

 

Botryosphaeria rot at eye end of Cox apple after CA storage showing characteristic purple colour

 

 

 

 

 

 

 

 

Storage rots (orchard diseases)

Disease

Varieties

Source

Entry

Weather factors

Cultural control

Fungicides

 

Nectria rot

(Nectria galligena)

 

Cox, Bramley, Gala

Egremont Russet

Cankers

Direct through lenticels, stalk end, eye end

Wet autumn at leaf fall.  Wet spring, summer

Removing cankers and macerate with prunings

Post-harvest copper sprays to protect leaf scars, sprays at bloom and petal fall

Pre-harvest sprays

 

Diaporthe rot

(Diaporthe perniciosa)

 See image below

Cox, Bramley,

Jonagold, Gala

Cankers, dead wood, mummies

Direct on mature fruit long-term stored

Warm and wet

Remove cankers, dead and weak wood during pruning

Rot usually not important enough to merit special control measures

 

Botrytis eye and core rot

(Botrytis cinerea)

Cox

Ubiquitous especially dead plant material, e.g. flowers

Direct from dead petals to eye or to core.  May require mature fruit to rot

Humid or wet

None

Possibly sprays during bloom

 

 

 

Diaporthe rot on Cox

 

 

 

 

 

 

 

 

 

 

 

 

 

Storage rots (orchard diseases)

 

Disease

Varieties

Source

Entry

Weather factors

Cultural control

Fungicides

Fusarium rot

(Fusarium spp)

 

 

Cox, Bramley, Cameo

Orchard soil, plant debris, cankers, dirty bulk bins

Wounds

Core rot

Rain, warm weather

Prune out old Nectria cankers and pruning snags.

Usually not important enough to merit special attention on most varieties.  On Bramley and Cameo apply fungicide sprays at blossom and petal fa

 

 Storage rots (store diseases)

Disease

Varieties

Source

Entry

Weather factors

Cultural control

Fungicides

Botrytis rot

(Botrytis cinerea)

 

All varieties

Plant debris, orchard soil, dirty bulk bins

Wounds. 

Infected stems

Store disease rapid growth at low temperatures

Careful picking to avoid wounds

Good control of pest and disease

Avoid muddying bulk bins and introducing debris such as leaves

Clean bulk bins

Pre-harvest sprays may give some control

Blue Mould

(Penicillium expansum)

 

All varieties especially Bramley

Plant debris, orchard soil, dirty bulk bins

Wounds, direct entry on over-mature fruit

Store disease

Careful picking and handling to avoid damage

Good control of pest and disease

Avoid muddying bins and introducing debris such as leaves

Clean bulk bins

Post-harvest dips/drenches aggravate the problem

Mucor rot

(Mucor spp)

 

All varieties

Orchard soil, dirty bulk bins

Wounds or through open eye in drench solution

Store disease rapid growth at low temperatures.

Wet harvesting

Avoid muddying bins and introducing debris

Clean bulk bins

Removing fallen fruit from orchard after harvest to reduce fungus population in soil

Store dry fruit

No fungicides are effective against Mucor

Post-harvest dips/drenches aggravate the problem