140 DISEASES OF CROP-PLANTS 



fungus is established in the soil and surface infection is taking 

 place, an examination of the trees, involving no more than an 

 initial clearing and periodic inspection of the crown and collar, 

 will directly save many lightly infected trees, and, indirectly, 

 by preventing the formation of new centres of distribution, save 

 very many more. All that is needed is to have the lower branches 

 pruned sufficiently for access to the trunk, a couple of labourers 

 to go on ahead and clear away weeds and earth for a foot or so 

 around the junction of roots and stem, preferably using their 

 hands or a blunt instrument to avoid wounding the bark, and 

 then to make a few minutes* investigation of each tree so pre- 

 pared. In addition to saving trees, such a system enables the 

 hopeless cases to be detected long before they otherwise would 

 be, and makes it possible to deal promptly with them. It is 

 justifiable to insist that in every clearing in which the disease 

 has become established such an inspection ought to be made at 

 least twice a year. 



The principles of the actual treatment are two in number 

 and very simple : {a) complete excision of diseased tissues ; 

 (b) exposure as complete as possible of the affected part and 

 its surroundings to freely circulating air, with the object of making 

 the conditions too drj^ for the fungus to exist. 



The cases which repay treatment are those arising from 

 surface infection, in which on inspection the local nature of the 

 infestation appears to be clearly defined. Severed roots should 

 as far as possible be removed ; cut surfaces should be cleanly 

 trimmed and treated with wound dressing ; excavations made 

 to get at the seat of injury should be left open. It should be 

 hardly necessary to say that the material removed must be 

 carefully disposed of. In many cases a few cuts with a sharp 

 knife will save a tree from an infection which would have meant 

 its certain death. 



Where the disease has been detected advancing along one or 

 more large roots but has not reached the collar, and it is desired 

 to give the tree a chance of recovery, after the diseased roots 

 have been cut away as much soil as possible should be dug out 

 about the junction of the main roots and as far back as they can 

 be conveniently followed, leaving the tree more or less on stilts. 

 This prevents the crossing over of the fungus at or near the collar, 

 and may very considerably delay the loss of the tree ; but if the 

 fungus, as is probable, exists on the outer roots, it will in time 

 get round in that region and come up each of the main roots 

 in turn as far as the point to which it has been bared. It is not 

 a measure to be recommended. It is better to have the tree out 

 and be rid of the fungus, but the temptation to get an additional 

 crop or two from some specially fine tree is sometimes hardly 

 to be resisted. 



The directions here given as to treatment apply equally to 

 limes and cacao, but as has been previously indicated, with the 



