Brown rot - disease cycle and epidemiology

  • Monilinia fructigena overwinters in the orchard either on cankers or as mummified fruit on the tree or ground under the tree.
  • These produce spores after rain in the summer sometimes as early as May but more usually in June, depending on temperature.
  • The spores are spread by wind to infect young fruitlets through wounds.
  • The fungus can only infect through wounds, but once in, can then spread from infected to healthy fruit in a cluster by mycelial spread.
  • Wounds can be caused by insects (especially codling moth), russet cracks, scab, growth cracks.
  • Free water is required for spore germination but once in the wound, further development is not dependent on rain.
  • Wounds are most susceptible when fresh and susceptibility declines with age.
  • Conversely, fruit is most resistant when young and susceptibility increases as the fruit matures.
  • Infected fruit rapidly become covered with buff-coloured pustules which serve as inoculum for other fruit, and are spread by wind and by insects attracted to the juicy rotting fruit.
  • Fruit infected near harvest remain symptomless and are harvested along with healthy fruit and stored.
  • The rot subsequently develops in store and spreads by contact to healthy fruit.
  • In the orchard, the fungus can spread from the rotted fruit into the fruiting spur forming a canker.
  • Rotted fruit may drop and form mummies on the ground or remain attached to the tree and mummify in situ.
  • The sexual state of the brown rot fungus occurs on overwintered mummified fruit, but is very rare in the UK and is not important in the epidemiology of the disease.
  • The fungus is favoured by warm humid weather.
  • Rain is essential to initiate sporulation, but not essential for fruit infection as fresh wound surfaces are moist.