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Apple Canker (Neonectria ditissima)

 

Mature canker with perithecia

Apple canker is one of the most important diseases of apple in the UK and parts of Europe and on susceptible varieties can cause serious losses.  as a result of cankers on trees and a fruit rot, both in the orchard and in store.

Symptom recognition in the orchard is generally straightforward.

  • Old cankers show as flaky dark brown strips of bark surrounded by swollen wound tissue.
  • Red (perithecia) or white (conidia) fruiting bodies may be present.
  • Cankers on young shoots generally have white fruiting bodies and result in shoot die back in summer.

 

Nectria rot

Canker control is difficult as the lifecycle and epidemiology allow the fungus to produces spores all year round and there are suitable entry points for infection on the apple tree all year round as well. Although the limiting factor is rain and wet seasons, particularly wet autumns, usually result in significant canker incidence in orchards and fruit, other factors may affect the susceptibility of the tree to canker, including variety, rootstock, soil type, soil water content, pruning and fertilizer regime.

Disease monitoring and forecasting is important.

  • Inspection of orchards for Nectria cankers during winter pruning and for shoot die back in spring/summer due to canker will give an indication of the problem in orchards.
  • In addition assessment of Nectria rot incidence during fruit grading from store will also give an indication of canker incidence in the orchard.

Control

In problem orchards routine treatments are required every year.  Effective control of canker requires an integrated approach with both cultural and chemical treatments.

  • In winter, prune out cankers where possible or pare back cankers on scaffold branches to healthy tissue. Treat with a suitable canker paint immediately after pruning.
  • If possible remove prunings from orchard and burn.  Otherwise pulverise or macerate  pruning debris taking care that pieces do not remain beneath the trees on the herbicide strip.
  • In summer prune out shoot dieback as soon as possible to reduce inoculum for fruit rot.
  • On young trees ensure that wounds are painted.
  • In orchards with low canker incidence at autumn leaf fall, apply a spray of a copper fungicide at 10% leaf fall and repeat at 50% leaf fall.
  • In orchards with moderate to high canker incidence apply a spray of tebuconazole (Fathom) before the end of leaf fall, followed by a spray of a copper fungicide at 10% leaf fall, then a spray of tebuconazole (Fathom) at 50% leaf fall with a second copper spray at 90% leaf fall.
  • Apply a pre-bud burst copper spray in the spring.
  • In planning the use of copper sprays, growers should check the current approval status and permitted number of applications of copper fungicides.
  • At bud burst spray dodine (e.g. Radspor) or dithianon (Dithianon) to protect bud scale scars against infection. Repeat at mouse ear.
  • Thereafter use dithianon or captan as part of the scab control programme. These products will give some protection against canker.
  • Dithianon + pyraclostrobin (Maccani) or pyraclostrobin + boscalid (Bellis) or cyprodonil + fludioxonil (Switch) will also give some control.
  • Orchards at risk from Neonectria rot can be identified in spring based on the incidence of cankered trees in the orchard (<5% = low risk, 5-25% = moderate risk, >25% = high risk) and the rot history from pack house records. The risk of Neonectria rot in store can then be further assessed based on the rainfall between blossom and harvest.
  • Apply sprays of captan or pyraclostrobin + boscalid (Bellis) or cyprodonil + fludioxonil (Switch) to orchards where a moderate to high risk has been identified, during blossom and at petal fall. These will give fruit some protection against Neonectria rot and in orchards with a high canker incidence, are essential if fruit is to be stored without significant losses beyond Christmas.
  • The same treatments can be applied pre-harvest in late July and August.
  • In orchards where a high canker risk has been identified, the best option may be to avoid chemical treatment and schedule the fruit for early marketing before Christmas to minimise losses.
  • The Neonectria risk of fruit from lower risk orchards is based on the volume of rainfall from blossom to harvest. In seasons when rainfall is above average this fruit may also need to be scheduled for early marketing if sprays have not been applied during blossom.

 

Fungicides approved for use on apple which are recommended to control canker or offer some incidental control when applied to control other diseases

Active ingredient   Trade name (examples) Fungicide group Fungicide action Safety to Typhs Other disease controlled or partly controlled
captan Captan 80 WDG, PP Captan 80 WG phthalimide P safe scab, Gloeosporium 
copper oxychloride (120-day authorisation which lasts until 14/07/17) Cuprokylt (EAMU 0832/2017) inorganic P safe scab (pre bud-burst), collar rot
cyprodinil + fludioxonil Switch anilinopyrimidine + cyanopyrrole P u scab, Monilinia spp., Gloeosporium, Alternaria, Botrytis, Penicillium, Fusarium, Colletotrichum
dithianon Dithianon Flowable, Dithianon WG quinone P safe scab
dithianon + pyraclostrobin Maccani strobylurin (QoI) + anilide P safe scab, powdery mildew
dodine Syllit 400 SC, Radspor 400 guanidine P safe scab
pyraclostrobin + boscalid Bellis strobylurin (QoI) + anilide P safe scab, powdery mildew, Gloeosporium, Alternaria, Botrytis, Penicillium
tebuconazole Fathom(EAMU  0712/2017), Folicur (EAMU 2647/2016) DMI P safe Powdery mildew

P          = protectant

SS        = sporulation suppressant

Fungicides for control of Neonectria ditissima – Safety factors

  Active ingredient Hazards  Harvest interval (days)   Max. no sprays Buffer zone
human fish + aquatic life

bees

width(m)
captan h, ir, c t

u

31 10 30
copper oxychloride h d

u

 Pre bb 4 50
cyprodonil + fludioxonil a, c d

u

3 3 30
dithianon h, ir, c d

u

28 See label –varies with product sm
dithianon + pyraclostrobin h, ir, c t u 35 4 40
dodine h, ir d

u

Dessert: pre-blossom, Culinary: early July none stipulated sm
pyraclostrobin + boscalid h d

u

7 4 40 m
tebuconazole h d

u

PH, Pre first leaf 1 sm

d = dangerous; h = harmful; ir = irritating, a = may cause allergic reaction, t = toxic

PH = post harvest; Pre bb = pre-bud burst, sm=statutory minimum of 5 m for broadcast air assisted sprayers

u=uncategorised/unclassified/unspecified, c=closed cab required for air assisted sprayers

Control in organic orchards

  • Cultural methods of control are the most important.
  • Copper fungicides are permitted in organic production at present and should be applied at autumn leaf fall and pre bud burst in orchards at risk from Neonectria.

 

Further reading