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Mycologia, BASIDIOMYCOTINA, APHYLLOPHORALES, STEREACEAE .

Crops attacked: apricot, .

Silver-leaf disease

Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images

[R]Description
As early as spring the leaves may turn pale green and show a metallic sheen (leaden-grey or silvery).
The affected leaves curl up and become necrotic. A red area occurs around the necrosis.
Symptoms are irregularly distributed on the tree : a part of the tree may stay healthy while the other is infected.
The disease spreads randomly in the orchards and it may affect up to 50% of the trees.
Carpophores, which can be seen on the trunks of dead trees, are fructifications of the fungus and appear as imbricated hard blades with a brown lower face, pale lilac on the margins.
This fungus may also occur in forests : birch ( Fagus silvatica ) and poplar ( Populus spp. ).

[R]Biology
Carpophores appear during the first autumn rains and generate basidiospores which are disseminated by the wind. When they set on wounds (eg. pruning wounds) the spores are carried through capilaries into the wood where the fungus develops and colonizes the branches and the trunk.
The resulting toxins are spread by the sap and cause the sheen aspect of the leaves which shows the following spring or even after several years.

[R]Epidemiology
Carpophores are formed in conditions of high relative humidity.
Basidiospores can germinate at 10 °C. in the presence of free water.
Development of the disease is favoured by the oceanic climate with mild winters and cool springs.

[R]Treatement
Pruning should be done relatively late and the resulting wounds should be treated with fungicidal paints using a brush.
Use special secateurs for pruning which spray a suspension of Thricoderma harzianum conidia on the wound (biological control).
Remove and burn the affected plants before autumn.

[R]Possible misleading
The damage caused by an acaricid.

[R] Images

1. Stereum purpureum , Silver-leaf of fruit-trees (GROSCLAUDE C., INRA)
   Silver-leaf of fruit-trees Silver-leaf disease on peach-tree twigs.
   
2. Stereum purpureum , Silver-leaf of fruit-trees (FAIVRE-AMIOT A., INRA)
   Silver-leaf of fruit-trees Silver like aspect of the plum-tree leaves infected by Stereum purpureum .
   

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