136 DISEASES OF CROP-PLANTS 



"Wherever a tree has died, unless strict measures have been 

 taken to control the fungus, the adjacent trees almost inevitably 

 contract the disease sooner or later. Such cases may develop 

 years after the origmal tree has been removed and the cause of 

 Its death forgotten, so that they have the appearance of being 

 sporadic. Examination of the position and age of supplies, and 

 the keeping of records of surveyed areas enable them to be 

 linked up with considerable certainty to previous losses. How 

 far such belated cases are evidence of the slow progress of the 

 fungus along the roots, or how far they are due to delayed in- 

 fection has not been ascertained, but the general evidence points 

 to the conclusion that the process of investment of mature trees 

 is a distinctly slow one. In a case definitely recorded a fully 

 infested dead lime tree was removed in October, 1914, and the 

 fungus {R. bimodes) was just coming up round the collar of the 

 next tree in the row, a very large and vigorous specimen, in 

 August, 1916. The variety of circumstances must produce wide 

 difterences, but it is judged that the two years taken in this case 

 is not an unusual period, and is in some cases considerably 

 exceeded. 



Typically an infested clearing in which the disease is of 

 several years' standing shows a few large open patches, each 

 representing perhaps a score of trees, with usually two or three 

 around its margin dead or dying, and several more on which the 

 fungus may be found. Sometimes two or three such patches 

 have coalesced. Scattered about are fresh centres in various 

 stages : a single tree, a gap of two or three trees in a row, with 

 another going, or a group of two or three trees in different stages 

 about a large stump. Of the supplies put in, some are several 

 years old and still thriving, others are dead within a few months 

 of being planted. On one cacao estate in a wet mountain district 

 the loss of about 150 trees appeared to be clearly traceable 

 to two original centres of infection. 



Counter Measures : I. Prevention 

 (a). In New Clearings. 



It would be a counsel of perfection to recommend the removal 

 of stumps or even of logs from new clearings in their earliest 

 stages. In most West Indian plantations such a policy is not 

 economically possible. But, in arranging and planting new 

 clearings for orchard crops, the probability that root disease 

 will occur should be kept in mind, and certain precautions can 

 be taken which will considerably reduce the trouble to be faced 

 when disease appears. 



First among these is provision for the construction, immediate 

 or when occasion and funds permit, of a complete and close 

 system of trench drains. To this end the arrangement of the 

 trees should be planned so that each block shall be isolated from 



