Cankers
Fungicides with good activity against Neonectria are limited.
- Copper fungicides e.g. Cuprokylt FL give good prolonged protection against Neonectria, but are phytotoxic and can only be used post-harvest and 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 Bellis (pyraclostrobin + boscalid) and Switch (cyprodinil + fludioxonil) are active against scab and storage rots and will also give some control of canker and Neonectria rot.
Control of Neoctria 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 before bud burst.
- Apply dodine or dithianon 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 cyprodinil + fludioxonil (Switch) will also give some control.
- In orchards with low canker incidence at autumn leaf fall, should it be approved, apply a spray of a copper fungicide at 10% leaf fall and repeat at 50% leaf fall. Copper also speeds up leaf fall and reduces the time when trees are susceptible to infection. 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.
- In orchards with moderate to high canker incidence apply a spray of tebuconazole (Fathom) before the end of leaf fall, 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. 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
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 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. Orchard trials are planned to investigate this.
- 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.