There are no recommended chemical control measures and so cultural control measures are equally applicable to organic production and conventional systems.
However, the growth regulator Regalis (prohexadione-calcium) used to control shoot growth can also reduce the incidence and severity of fireblight shoot infection. Regalis is applied in late bloom to suppress shoot growth so its main effect is on secondary fireblight rather than on primary blossom infection.
Control is dependent on understanding the disease, vigilant monitoring, prevention and rapid action when symptoms are seen.
- Make routine inspections for fireblight symptoms soon after leaf fall, during winter pruning, soon after bud break, about mid-June and in late July to early August.
- Inspect young trees more frequently.
- Make additional inspections: if there is frost damage to blossom, following damaging storms, following warnings of fireblight, or following reports of fireblight elsewhere.
- Remove and burn diseased parts of young apple trees as soon as possible. Cut through healthy wood well below diseased wood to ensure thorough removal. On mature apple trees this might not be cost effective and is less urgent.
- On twigs or shoots cut out 12 ins below stain; on branches (of 1 in or more in diameter) cut out at least 18 ins below stain. Start exploratory knife cuts in healthy tissue first and move up.
- Disinfect tools between cuts and between trees preferably using a recommended disinfectant (3% Hycolin, Sudol or Clearsol). Thorough removal of plant residues from the tools is essential for maximum effectiveness of disinfectants.