Phytophthora rot (Phytophthora syringae; Phytophthora cactorum)

Phytophthora

The characteristic symptoms are a firm rot, mid-dark brown in colour and often marbled or blotchy

The life cycle and epidemiology of this soil-borne fungus involves survival in the soil as resting spores (zoospores).

These germinate in wet weather releasing swimming spores (zoospores) which splash onto low hanging fruit causing rotting.

Symptomless infected fruit are picked and stored and initiate rotting and spread in store.

No forecasting methods have been developed for Phytophthora fruit rot but rot risk assessment should be undertaken pre-harvest. This risk of Phytophthora rot pre-harvest for an orchard can be determined from the orchard rot history, the % bare ground, the proportion of the crop less than knee-height above the soil and hence at risk from soil splash, and the accumulated rainfall 15 days pre-harvest.

Control

The risk of rotting in store can be reduced by a combination of cultural and chemical control  measures including:

• Mulching the soil surface, selectively picking so only fruit above knee-height are stored
• And/or fungicide sprays – captan or Bellis (pyraclostrobin + boscalid) sprays at one month and 14 days pre-harvest.
• Alternatively, the decision on action on Phytophthora risk can be made at harvest and fruit scheduled for early marketing to minimise losses where a risk has been determined.

Control in organic orchards

• In organic orchards, control of Phytophthora rot in stored fruit is based on cultural measures and the use of pre-harvest risk assessment to determine the storage potential of the fruit.

Fruit rot in store in the UK is caused mainly by Phytophthora syringae. The rot occurs sporadically and significant losses in store are associated with wet harvests.  All apple varieties are susceptible.

Phytophthora rot - additional information