What is brown rot?

Brown rot is a fungal disease that can cause real trouble on apples, pears, apricots, cherries, nectarines, peaches, plums, greengages and damsons, when fruit is ripening, as well as during blossom time. It is caused by three different fungi: Monilinia fructigena, Monilinia laxa and Sclerotinia fructigena. It also infects blossoms of fruit trees, which become brown in appearance; the problem may persist in the trees well into early summer.

It is when the fruits are beginning to ripen, whether they be apple, pear, plum, cherry, peach, nectarine or apricot, that the brown rot fungus becomes really active. The conidia spores enter the fruit through small wounds or bird pecks, and germinate. The spores soon develop and the fungus spreads over the fruit. Affected fruit shows small spots of rot that get larger and eventually cover the entire surface, with lighter-coloured spore spots. If the weather is favourable it is able to destroy a very significant proportion of the fruit crop. Warm and humid days suit the fungus best. It may even affect young shoots.

Brown rot
Brown rot, photo courtesy of Barockschloss/flickr.com

How to treat brown rot

The principal methods of treating brown rot are preventive measures and orchard hygiene.

  1. Choose varieties resistant to brown rot if possible, such as Harglow Apricot and Venture Peach.
  2. Plant trees in full sunshine, and ensure that soil drainage is good.
  3. Summer prune the trees to ensure that the canopy remains open to light and with a good circulation of air.
  4. Irrigate underneath the tree, and try not to wet blossom, foliage and fruit.
  5. Always remove all fruit from the tree after harvest, and remove all fruit and twigs that have fallen to the ground. Burn or dispose of safely and definitively.
  6. Remove affected branches, fruit and shoots. Disinfect secateurs before, during and after the process.
  7. Seal any large cuts and wounds.
  8. Place all pruned material into the non-recycling bin, or burn it.
  9. Remove infected fruit, and dispose of it in the same way, non-recycling. Do not try to compost fruit or prunings.
  10. If you are considering spraying with fungicide, choose an environment-friendly product, and spray at a time when there is no risk of harming beneficial insects. Spray only in dry weather conditions. We recommend seeking expert help in such cases.

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