214 Silver-Leaf Disease, HI 



rate, modified methods of injecting trees invaded by fungi in the wood, 

 might be tried with some prospect of success. 



While the above experiments were being carried out with dyes, 

 other toxic substances also were injected in the roots of silvered trees in 

 the same way, but with little or no success. Of two trees injected with 

 a weak solution of ferrous sulphate (made up 1 in 1000) one doubtfully 

 recovered and the other remained silvered. Solutions of corrosive subli- 

 mate and quinine sulphate (made up 1 in 1000) were without effect. 

 Sodium arseniate, on the other hand, made up at the same strength, 

 had a rapidly toxic effect upon the injected tree and although the 

 strength of the solution was quickly reduced to 1 in 20,000 all the 

 leaves withered except on one branch low down on the side away from 

 the place of injection. These leaves remained silvered but by the fol- 

 lowing year all the upper part of the tree was dead and only a few sucker 

 shoots, which were healthy, remained. 



7. TREATMENT IN FRUIT PLANTATIONS. 



In the light of the foregoing statement it will be recognised that 

 'there is at present no known curative treatment for this disease that 

 can be apphed on a commercial scale with prospect of success. The 

 only sound method of control is along the lines advocated in the previous 

 paper and advised in the leaflets recently issued by the Board of Agri- 

 culture. Where silvered branches have been properly cut back and 

 dying trees have been grubbed so that Siereum ftirpureinn is not allowed 

 to fructify in the plantations, the disease has been kept under control 

 and its spread has been so greatly checked that it has ceased to be a 

 menace in some of the largest commercial plum gardens in the country, 

 in which silver-leaf disease was formerly common. On the other hand, 

 if the fungus is allowed to fructify with impunity the disease spreads 

 with alarming rapidity in Victoria plums. 



The following table kindly supplied by Mr E. Neaverson is an 

 illustration of the rapid spread of silver-leaf disease in a Victoria plum 

 plantation near Wisbech, even where conditions were not specially 

 favourable for the extension of the disease. Some of these trees were 

 plugged with sulphate of iron as described earlier in the paper and the 

 most severely afiected trees were cut down each winter though Stereum 

 purpurenm often developed on them before the trunks were removed 

 from the plantation : 



