255 



Careless pruning, unsatisfactory drainage and a deficiency ut 



lime are especially to be avoided. The application of artificial 

 fertilizers, particularly those of highly nitrogenous character, 

 induces ".soft" growth, with its greater liability to injury by 

 frost and by insects. It is evident from the observations here 

 put forward that those stone-fruit trees and other trees and shrubs 

 annually subjected to pruning are much more likely to fall 

 victims to Silver leaf than those which are not so treated. In- 

 discriminate pruning, and the cutting off of old branches for 

 fire-wood, as was done in war-time, pave the way for the entrance 

 of the fungus if the cut surfaces are not immediately treated. 

 The following primary preventive measures are recom- 



m 



1. The destruction of Stereum pur pur earn wherever it occurs, 

 whether it is growing as a parasite or as a saprophyte. 



2. If localised silvering in the upper set of branches of a 

 tree is noticed, the silvered branches should be cut off without 

 •delay below the limit of discoloration of the wood. Many trees 

 have been saved from total destruction where this method has 

 been followed. Should, however, the lowest branches of a tree 

 be affected, there is little hope of recovery, since the fungus is 

 then present in the main stem. Such trees should be grubbed 

 up before the fructifications develop, usually about September. 



3. Whenever a branch is amputated, it is essential that the 

 branch should be cut off as near as possible to the main stem or 

 to the point of origin in order to encourage more rapid 

 " callusing/' A clean cut with a knife should follow the saw, 

 especially where a jagged surface has been left. When pruning 

 branches of the hosts mentioned on pp. 242, 243 of this paper, the 

 cut surface should be protected immediately, thus preventing the 

 .spores of the fungus, which are blown about by the wind, from 

 penetrating the host. Stockholm tar or its equivalent being one 

 of the cheapest substances for protecting the wounded surface 

 can be used for commercial purposes, whereas on a small scale, 

 grafting-wax may be employed. 



4. Kemovai of all dead and diseased wood from the plan- 

 tation, since the fungus in the wood will soon develop fructifica- 

 tions, the spores from which are a great danger to the trees in 

 the vicinity. Diseased branches should not be used for fencing, 

 as this involves the same danger as when left in piles in the 

 orchards. Storing of the wood under such dry conditions as 

 prevent the development of the fungus should be aimed at. 

 An alternative method, which may be adopted in large planta- 

 tions, is the conversion of such cut off branches into charcoal in 



the field. 



5. In plantations where the plough is used for catch crops, 

 it is difficult to prevent injury to superficial roots, but additional 

 injury by the spade may be minimised by a careful use of that 

 implement, and by the pulling up of suckers. 



6. Varieties of plums grown on their own roots produce only 

 a few or scarcely any suckers, and hence the planting of such 

 Tarieties is advisable whenever circumstances permit. 



7. The planting of resistent or less susceptible varieties of 



