Pre-harvest
- In orchards at risk from Phytophthora rot, particularly where orchard rot history has indicated a significant incidence of Phytophthora rot in store following a wet harvest, two fungicide sprays of captan or Bellis (pyraclostrobin + boscalid) to low hanging fruit, one month and 14 days pre-harvest will give some protection to fruit from Phytophthora rot.
- Alternatively Fubol Gold WG (mancozeb+metalaxyl-M) has off-label approval for use as a spray to the orchard floor for control of Phytophthora fruit rot, up to two treatments per season applied after leaf fall but before green cluster.
- Captan or Bellis are the preferred orchard treatment at present.
- Use of mancozeb + metalaxyl-M in this way has a high risk of Phytophthora species developing resistance to it.
- This would affect not only control of Phytophthora fruit rot but also of other Phytophthora diseases of apple such as crown and root rot.
Avoiding fungicide resistance
- The risk of resistance to captan is very low, however the risk of resistance to metalaxyl-M is high.
- Monitoring for resistance in P. syringae isolates has detected isolates which are slightly less sensitive, however there was no evidence of reduced control of the fruit rot.
- Resistance of P. cactorum to metalaxyl has been demonstrated in other crops such as strawberry crown rot but none has been detected in apple.
- The resistance status of Phytophthora spp. to Bellis (pyraclostrobin + boscalid) is not known.