Apple varieties vary somewhat in their susceptibility to woolly aphid (e.g. Bramley is more susceptible than Cox) but commercially-grown apple varieties are not resistant. The relative susceptibility of varieties has not been characterised adequately.
- Resistant rootstocks have been bred by crosses between Northern Spy, which is highly resistant, and various Malling rootstocks which resulted in the Malling-Merton (MM) series of apple rootstocks which are highly resistant to woolly aphid. However, the rootstock does not confer resistance to the scion.
- The Malling-Merton rootstock MM106 is a semi-dwarfing woolly aphid resistant rootstock which is widely grown in the UK.
- The MM rootstocks have been very valuable in countries where root infestation occurs (Australia, South Africa and North America) but the resistance of rootstocks is of limited benefit in the UK where root infestation does not occur.
- In other countries, isolated cases of infestation by local races of woolly aphid occur on resistant rootstocks.