Amputation Only Treatment For Silver Leaf

Press, Volume CVII, Issue 31499, 13 October 1967, Page 6

Amputation Only Treatment For Silver Leaf

The incidence of the fungus disease silver leaf, or silver blight as it is often referred to, frequently necessitates the removal of part or all of a plant, perhaps of long standing in the garden. It could be a most beautiful flowering ornamental, or a prolific fruit tree, for the host range is very wide as is indicated by the list compiled from records kept by the Plant Diseases Division of the Department of Scientific and Industrial Research, Auckland. Silver leaf is first noticed when the leaves turn a silvery colour, giving them a metallic lustre, and early attacks are usually confined to the smaller branches, spreading from there. If the disease is left unchecked at this stage, the whole tree or bush steadily succumbs, showing a gradual decline of vigour, and eventually dying.

Leaf structure and other factors influence the appearance of the disease symptoms in particular host species. The presence of fructifications of the fungus on dead wood does not necessarily mean therefore, that silver leaf disease is apparent or even occurs in that species. Nevertheless recently dead or dying wood of all the following species can be invaded by it and if the wood remains moist, fructifications or fruiting bodies are produced. These look like brackets and are produced on the external surface from which spores are liberated. These are released in autumn and dispersed by wind and rain to suitable hosts. Entry is through neglected pruning cuts or damaged wood and infected wood usually shows a brown discolouration. Fructifications can occur oh recently dead wood, including stumps and branches of felled trees, and on dead or dying branches of living trees and shrubs. It never enters through the leaves, being confined to woody tissues. As ye. there is no control and once the presence of silver leaf has been verified the only remedial measures possible. providing the subject is not too badly affected, is the removal of the infected limb. This must be cut back 1 at least a foot below the last owtwardly-visible symptoms as the disease does not remain localised at these points but may be well down in the healthy wood. The cut should be immediately pared and the surface sealed.

Wood on which brackets of this fungus are observed should not be left lying around, but should be burnt at once.

There is no risk of spreading the disease by tools as, for instance, in the case of fire blight. It has been recorded in the following: Acacia decurrens, Aesculus hippocastanum, Betula alba and Betula papyrifera occidentalis, Casuarina sp., Cotoneaster sp., Crataegus oxycantha and Crataegus monogyna, Cupressus macrocarpa, Cydonia oblonga, Cytisus proliferous and Cytisus scoparius, Eriobotoya japonica, Escallonia macrantha,

Eucalyptus ficifolia, Fagus sylvatica, Fraxinus excelsior, Lupinus aboreus, Malus sylvetris, Nothofagus cliffortoides and Nothofagus solandri, Pittosporum crassfolium and Pittosporum tenuifolium, Populus nigra italjca and Populus tremuia, Prunus amygdalus, Prunus armeniaca, Prunus avium, Prunus domestica, Prunus lusitanica, Prunus persica and Prunus salicina, Pyrus communis, Rhododendron species, Ribes grossularia, Ribes nigrum and Ribes sativum. Robinia \pseudocacia, Rubus tdaeus, Salix fragilis and Salix capraea, Syringa vulgaris, Ulex europaeus, Prunus ceraseus.