Rootstocks
Rootstocks vary in their susceptibility to P. cactorum.
- M.9 appears most resistant, but reports suggest regional differences in rootstock susceptibility.
- M.2, M.7, M.26 and MM.111, which are very resistant under UK conditions are susceptible in parts of North America.
- Rootstocks MM.104 and MM.106 and Merton 789 are considered in general to be very susceptible.
- Rootstocks available from abroad also vary in susceptibility to Phytophthora.
Scion varieties
- Collar rot is predominantly a disease of Cox and occasionally James Grieve in the UK, but in New Zealand and Europe has been recorded on other varieties including Laxton’s Superb, Ribston Pippin and Ellison’s Orange.
- In the UK collar rot rarely occurs on trees less than 10 years old.
- Cox on M.2, M.9 and M.26 are particularly prone to attack.