82 



Silver Leaf Disease. 



[Apr., 



ance of silvered foliage. By this means it is possible to save 

 the life of the tree, providing that the silvered branches are cut 

 back to clean wood. 



The fungus causing Silver Leaf spreads iii the wood by 

 means of mycelium, which may be traced by the dark stains in 

 the wood. If infected wood — even though in a living condition 

 — is not removed beyond these dark stains the fungus is capable 

 of spreading to other portions of the tree, and if allowed to go 

 on unchecked will ultimately kill the host. 



A dead plum or other fruit tree killed by Silver Leaf Disease 

 is a source of danger to any other specimens in the orchard, for 

 the fungus then produces fructifications bearing spores 

 which are capable, after being distributed by wind or other 

 agencies, of infecting healthy trees, providing suitable weather 

 conditions prevail, entrance being afforded by means of cracks 

 in the bark, wounds, or unprotected pruned surfaces. 



Since the introduction of the Silver Ijeaf Order of 1919 

 especially the cutting out of infected wood has been practised by 

 fruit growers, and there has been a tendency occasionally to use 

 the infected wood for posts, either to stop gaps in the fence 

 around the orchard itself, or elsewhere on the holding or farm. 

 Unfortunately, however, many growlers are under the impres- 

 sion that if such wood is painted with tar the fungus will 

 be rendered incapable of producing the incrustations or bracket 

 shaped bodies bearing the spores. 



The Ministry therefore conducted experiments to ascertain 

 whether tar really had the power to prevent the fructifications of 

 Stereum purpureum from appearing on infected wood. A 

 preliminary trial was made in an orchard formerly 

 severely attacked by Silver Leaf, l^elongin^' to Mr. T. 

 Hatley, J. P., of West End, near Southampton. It was particu- 

 larly desirable that the experiment should be conducted in the 

 district, since the amount of disease present in the area wa& 

 considerable, and many growers had suffered heavy losses owing 

 to the spread of the disease. 



On 11th November, 1920, three posts were selected for the 

 experiment, which were known to be infected and Had been sawn 

 from plum trees of the Victoria variety. 



The posts were placed in the following order : — 

 Post No. 1, Bark removed. 

 Post No. 2, Bark not removed. 

 Post No. 3, Control. 

 Owing to bad weather it was impractical to paint with tar until 



