1905.] 



Larch Canker. 



309 



The general appearance of the fungus and the injury and 

 resin-flow following its attack are clearly shown in the 

 accompanying illustration. 



As a broad rule, it may be stated that when trees under ten 

 years of age are attacked by canker, they are either killed out- 

 right, or are so deformed that if they continue to grow they are 

 of very little value for timber. The reason is that in the case of 

 seedlings or very young trees, the main stem is the part usually 

 attacked, whereas in older trees the bark of the trunk becomes 

 so rigid that it is impervious to the punctures of aphides or to 

 injury by late frosts ; and the only chance of infection is when 

 branches are broken off, or more or less cracked at the point 

 where they leave the trunk. 



When a young tree is once attacked it very rarely recovers, as 

 the mycelium spreads in the tissues and starts new wounds at 

 some distance from the original point of infection. 



As a safeguard against inoculation taking place through 

 fissures in the bark caused by late spring frosts, it is advisable 

 not to form seed-beds nor plant larch in low-lying damp posi- 

 tions, where not only are the plants most exposed to frost, but 

 the conditions favour the presence of the aphis. 



Seedlings and young trees can be protected against the larch 

 aphis by spraying with the following emulsion : — Dissolve half 

 a pound of soft-soap in two gallons of hot water, then add two 

 gallons of paraffin, and mix thoroughly until the ingredients do 

 not separate on standing. One gallon of this stock emulsion 

 should be diluted with fourteen gallons of water ; it is then 

 ready for use. 



The rank growth of grass and weeds round young trees 

 greatly favours the development and spread of canker by 

 keeping them constantly moist. 



Trees that are badly diseased should be removed and burned. 



Great care should be taken not to injure the bark of young 

 plants when lifted from the nursery, or in planting, as is often 

 done when the turf is pressed firmly round the stem by the heel 

 of the planter. 



A rather more detailed account of this disease, illustrated by 

 one coloured and two other plates appeared in the Journal in 

 September, 1902. 



