Blossom wilt

What is blossom wilt?

Blossom wilt is a fungal disease of trees, especially fruit trees, 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 more commonly causes the disease known as brown rot in the fruit.

Many top fruit are affected, including apples, pears, plums, cherries, nectarines, peaches, apricots, and ornamental varieties.

The damage begins at flowering time in mid-spring, but becomes more obvious as shoots die back in late spring and early summer.

Symptoms

You may see the following symptoms:

• Brown and shrivelled blossoms and leaves on the fruiting spurs at flowering time
• Small, buff-coloured pustules of the causal fungi on dead tissues. Usually seen under wet conditions
• Severity varies greatly from year to year, depending on weather conditions at the time of flowering

Control

Non chemical control

• Minimise carry-over of the pathogens by removing all brown, rotted fruit promptly and composting. 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
• Prune out and burn infected spurs and blossoms to reduce the amount of fungus available to infect fruit
• Choose resistant cultivars: apricots ‘Monique’ and ‘Moorpark’; plums ‘Jefferson’, ‘Marjorie’s Seedling’, ‘President’ and ‘Reine Claude Violette’ are resistant. Apple ‘Lord Derby’ is very susceptible

Chemical control

Difenoconazole (Westland Plant Rescue Fungus Control) is labelled to control blossom wilt on cherries, plums, prunes, gages, damsons and ornamental trees. Fungicides applied for other purposes, such as scab control, may give some incidental control though this is not claimed by the manufacturers.

Download

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

Biology

Fruit becomes infected through wounds, particularly bird damage. Affected fruits exhibit brown rot, mummify and remain hanging on the tree and, where they touch the bark, 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.