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.
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 Neonectria 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 Neonectria 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 (check status of current authorisation) at 10% leaf fall and repeat at 50% leaf fall.
- In orchards with moderate to high canker incidence apply a spray of tebuconazole (Fathom, Folicur) before the end of leaf fall, followed by a spray of a copper fungicide at 10% leaf fall, then a spray of tebuconazole (Fathom, Folicur) at 50% leaf fall with a second copper spray at 90% leaf fall. At the time of up-dating this information in January 2024, copper was not approved for use on apple, but various products have been authorised for use as 'emergency authorisations' in the past, so growers and agronomists should continually check the latest status of copper products.
- Should copper be approved for use, 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 400, Syllit 400 SC) or a dithianon based product (Dithianon, Delan Pro) to protect bud scale scars against infection. Repeat at mouse ear.
- Thereafter use dithianon based products 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, Clayton Core | phthalimide | P | safe | scab, Neofabraea |
| cyprodinil + fludioxonil | Switch | anilinopyrimidine + cyanopyrrole | P | u | scab, Monilinia spp., Neofabraea, Alternaria, Botrytis, Penicillium, Fusarium, Colletotrichum |
| dithianon | Dithianon WG | quinone | P | safe | scab |
| dithianon + potassium phosphonate | Delan Pro | quinone | P | safe | scab |
| dithianon + pyraclostrobin | Maccani | strobylurin (QoI) + quinone | 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, Neofabraea, Alternaria, Botrytis, Penicillium |
| tebuconazole | Fathom(EAMU 0834/2019), 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 |
| cyprodinil + fludioxonil | a, c | t | u | 3 | 3 | 30 |
| dithianon | h, ir, c | t | u | 42 | 6 | sm |
| dithianon + potassium phosphonate | a, ir, c | t | ir | 35 | 6 | 30 |
| dithianon + pyraclostrobin | h, ir, c | t | u | 35 | 4 | 40 |
| dodine | h, ir | t | u | Dessert: pre-blossom, Culinary: early July | none stipulated | sm |
| pyraclostrobin + boscalid | h | t | 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.
- Should copper fungicides be approved in organic production, they must be applied at autumn leaf fall and pre bud burst in orchards at risk from Neonectria.