70 THE LARCH CANKER 



laid stress on preventing wounds when planting young 

 trees ; and Massee, on finding that infection could take 

 place through the punctures made by Ghermes dbietis, 

 declared that, if this insect could be suppressed, canker 

 would cease to be an epidemic disease. 



All these suggestions have proved useless in obviating 

 the disease, and foresters have been forced to adopt other 

 means for reducing the pecuniary loss for which canker is 

 responsible. One doctrine is that larch-growing should be 

 confined to situations and soils which have proved capable 

 of bearing healthy plantations. But since this rules out the 

 majority of districts in which larch is at present grown, it 

 is a confession of failure except in a few favoured localities. 

 Sir Donald Munro Ferguson has adopted, at Novar, a method 

 of treating larch which was described by Somerville (1906) 

 in the Journal of the Board of Agriculture. He plants pure 

 larch at 3,500 to the acre, the vast majority of which become 

 cankered. At the age of 16-20 years he cuts out all but 

 300-500 of the best trees, and is able to sell the 3,000 or so 

 thinnings for 20 .to 25. The lateral dead branches are 

 removed and the remaining larch are underplanted with 

 beech, or preferably such conifers asPicea sitchensis, Pseudo- 

 tsuga Douglasii, Tsuga albertiana, Thuja plicata, Cupressus 

 lawsoniana, and Abies grandis. 



In most plantations it will be possible to select 10 per cent, 

 of healthy trees, and the 300-500 trees that are left may 

 be exempt from canker during the remainder of their lives. 

 But obviously the treatment will be impossible in woods 

 where, as sometimes happens, even the best trees have three 

 or four cankers apiece. Nisbet (1907) criticizes the system 

 on the ground that the pure larch woods make an excellent 

 breeding-ground for the fungus, and become a source of 

 danger to all the intermixed larch woods in the district. 



We need therefore some method by which canker can be 

 prevented, and the method of infection which I have described 

 as accounting for the greater number of dangerous cankers 

 suggests a treatment which may possibly prove helpful in 

 preventing the disease. Until successful experiments have 



