Cankers – paints
Wounds do provide entry points for Neonectria and if used correctly paints can provide protection. Canker paints contain chemicals active against Neonectria and are applied to pruning wounds or pared back cankers to provide temporary protection against infection while the tree develops its own protective callus layer. The value of treating pruning wounds with paints is often questioned, for if they are not treated rapidly the paint can act as a seal on fungal infection that has already occurred.
Other coatings (e.g. BlocCade) contain no fungicides but provide a physical coating to protect wounds against infection by fungi such as Neonectria. To be effective, they must be applied immediately after pruning.
- Treat pruning wounds on trees, especially those in cankered orchards and in young orchards where it is essential that the scaffold branches remain canker free.
- Paints must be applied to the wound or pared back canker immediately, and at the very least within one hour of pruning.
- Apply to larger cankers after paring back, especially those on the trunk or scaffold branches.
- Time of application is not specified but should be applied as soon as possible after the pruning or paring wound is made.
- In AHDB Project TF 223 (Improving integrated pest and disease management in tree fruit), research assessed the effect of applying control products to treat pruning wounds using secateurs which incorporate a chemical dispenser. This technique achieved significant reductions in canker number. Applying Folicur (tebuconazole) either alone or in combination with BlocCade (a physical acting barrier to spore germination) gave best results.
Canker – sprays
Fungicides with good activity against Neonectria are limited.
- Copper fungicides (e.g. Funguran Progress) give good prolonged protection against Neonectria, but are phytotoxic and can only be used pre-bud burst. 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.
- Fungicides that are mainly active against apple scab such as dodine, dithianon and captan, also have some protectant action against Neonectria.
- Similarly pyraclostrobin + boscalid (Bellis) and cyprodonil + fludioxonil (Switch) are active against scab and storage rots and will also give some control of canker and Neonectria rot.
Control of Neonectria in orchards presents a particular challenge. Entry points for infection are available all year round, inoculum (either conidia or ascospores) is available all year round and the rain, essential for Neonectria sporulation and infection, often makes timely spraying impossible. Therefore the strategy for control, especially in cankered orchards, must be to protect at key times to limit infection.
- In canker risk orchards, apply a spray of a copper fungicide (check status of current authorisation) before bud burst.
- Apply a dodine or dithianon based spray at bud burst and mouse ear to provide protection on bud scale scars.
- 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.
- In orchards with low canker incidence at autumn leaf fall, it used to be commonplace to apply a spray of a copper fungicide at 10% leaf fall and repeat at 50% leaf fall. However, the last authorisation for copper hydroxide (Funguran Progress) was only permitted in the spring (pre bud-burst) on organic orchards up to 5 years old. Copper also speeds up leaf fall and reduces the time when trees are susceptible to infection.
- In orchards with moderate to high canker incidence, apply a spray of tebuconazole (Fathom, Folicur) before the end of leaf fall, 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.
- Tebuconazole applied post-harvest but before leaf fall is reported to harden the wood of apple shoots and reduce their susceptibility to Neonectria infection.
Fruit rot – sprays
Recent inoculation experiments have shown that fruit is most susceptible to infection at blossom and petal fall. Therefore it is important to apply protectant sprays at this time.
- Apply sprays of captan or dithianon + potassium phosphonate (Delan Pro) or pyraclostrobin + boscalid (Bellis) or cyprodinil + fludioxonil (Switch) 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.
The recent inoculation studies indicate a slight increase in fruit susceptibility to Neonectria ditissima pre-harvest, but it is not known whether there is any benefit from additional sprays at this time and there is the risk of fungicide residues in fruit from the late applications.
- 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.
Avoiding fungicide resistance
- The risk of resistance developing to fungicides is minimal as either the fungicides are multisite compounds, such as captan, or they are rarely sprayed intensively.