Brown rot fungal disease affecting fruit trees
Question: I have an Annie-Elizabeth apple tree which I planted next to a Victoria plum tree. After three good years, this time the apples grew to tennis ball size then went bad all through while still on the tree. They dropped off eventually. What went wrong? (E Teverson, via email)
The problem you have is a fungal disease called brown rot, which affects apples, pears, plums, cherries and other fruit and ornamental trees, causing a brown, spreading rot in fruit. It is caused by the same fungi that cause blossom wilt of the flowers and fruit spurs.
Brown rot is a fungal disease of top fruit, caused by the fungi Monilinia laxa and M.fructigena.
Many ornamental and fruit trees are affected, including apples, pears, plums, cherries, nectarines, peaches, apricots, including ornamental varieties.
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Rotting fruit are found from mid-summer onwards. Fruit becomes infected through wounds. Affected fruits mummify and may remain hanging on the tree and where they touch the bark they cause small infections (cankers).
The fungus remains in the dead fruit and cankers over winter and releases spores in the spring to cause the blossom wilt phase of the disease. These infections in turn release spores to infect wounded fruit.
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The main symptoms are what you have already seen: brown rot in the fruit, spreading out from wounds, especially those made by birds, codling moth (see next item) and apple scab infection.
Buff-coloured pustules of the causal fungi on the fruit surface, often in concentric rings, usually seen under wet conditions.
At flowering time the same fungi cause blossom wilt, where blossoms and leaves on fruiting spurs turn brown and shrivel Severity varies greatly from year to year, depending on weather conditions.
Minimise carry-over of the pathogens by removing all brown rotted fruit promptly and composting. Don't keep it on the tree.
Brown rot infects through wounds, especially those caused by birds, so if possible, net to reduce bird damage.
Prune out and burn infected spurs and blossoms to reduce the amount of fungus available to infect fruit.
The fungicide difenoconazole (Westland Plant Rescue Fungus Control) is labelled to control brown rot on cherries, plums, prunes, gages and damsons. Spraying susceptible trees at the beginning, peak and end of flowering may reduce the severity of the disease. Fungicides applied for other purposes, such as scab control, may give some incidental control though this is not claimed by the manufacturers.
•This article was first published on December 10, 2011.