What is brown rot?

Brown rot is a fungal disease of tree fruit, caused by the fungi Monilinia laxa and M. fructigena. The two fungi are very closely related and indistinguishable to the naked eye. M. laxa more commonly causes blossom wilt on pears and stone fruit, and a specific form, M. laxa f. sp. mali is restricted to apples. M. fructigena can cause brown rot in most fruit trees.

Many fruit trees and their ornamental varities are affected, including apples, pears, plums, cherries, nectarines, peaches and apricots.

Rotting fruit are found from mid-summer onwards.

Symptoms

You may see the following symptoms:

• Brown rot in the fruit, spreading out from wounds, especially those made by birds, codling moth and apple scab infection
• Affected fruit either fall, or remain hanging on the tree in a mummified state
• 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 at flowering

Control

Non chemical control

• Minimise carry-over of the pathogens by removing and disposing of all brown rotted fruit promptly. To dispose of fruit, you can bury them at least 30cm (1ft) below the soil surface. Do not allow rotted fruit to remain on the tree
• Brown rot infects through wounds, especially those caused by birds, so if possible, net to reduce bird damage
• If practical, prune out and burn infected spurs and blossoms to reduce the amount of fungus available to infect fruit
• The plums ‘Czar’, ‘Jefferson’, ‘Ontario’ and ‘President’ have some resistance

Chemical control

No fungicides are available to amateur gardeners for the control of brown rot.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: storing and disposing safely

Biology

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.