The actual risk of attack on a particular host or variety is dependent on the season’s weather and on the growth stage (e.g. spring blossom, late blossom, soft shoot growth coinciding with damaging storms) as well as inherent susceptibility. Young trees are particularly susceptible.
Susceptible hosts include:
- All the major pome fruits, including pear, apple and quince
- Ornamentals, including hawthorn, contoneaster, pyracantha, stransvaesia (Photinia), white beam and mountain ash.
The high risk apple varieties are:
- Braeburn, Gala, Egremont Russet, Fuji, Ida Red, James Grieve, Jonagold.
- Late flowering cider apples e.g. Vilberie, Brown Snout.
Susceptible rootstocks include M.9 and M.26.
- In some warm climates, Gala on M.9 and M.26 is particularly susceptible with rapid stem invasion reaching to the rootstock.