Jan. 1908.] 



23 



Plant Sanitation. 



Numerous instances have been seen where diseased trees just coming into 

 bearing have succumbed, and signs of old stumps surrounding them have been 

 noticed. These examples would bear out the opinion of Mr. Hart that the disease 

 has been present in the colony for a considerable time. 



It is only recently that it has assumed dangerous proportions. On one estate 

 alone in the Cedros district, out of a total of 25,000 trees, 3,000 have been cut down 

 within the last twelve months, and many more are either dead or in a diseased con- 

 dition, and in many other places the disease is already a serious annoyance- 

 There is undoubtedly danger of further spread. This danger is emphasized 

 by the recent rapid spread through some estates in the Cedros district, and if con- 

 ditions favour its development and proper remedial measures are not taken to check 

 it, the coconut industry of Trinidad will materially suffer. 



Already some of the smaller proprietors are beginning to feel the loss of 

 returns, and this loss will be felt the more severely if the present prices for coconut 

 and their products do not hold. 



Samples of soil from around the roots of diseased trees have been investigated 

 microscopically, and sterile mycelium, which appeared to agree with that found 

 inside diseased roots, was present in them. This would suggest that the mycelium 

 is capable of spreading through the soil. This mycelium may be capable of 

 attacking and killing the younger rootlets and then entering into the larger 

 ones. The entry of the mycelium into the roots is still an unsolved problem, 

 but evidence tends to show that the larger roots first show signs of infection where 

 the small rootlets join them. In no case has the mycelium been noticed on the 

 exterior of the roots, and it would seem that it has to depend upon the rot of the 

 smaller roots for its distribution. 



The roots of several young supplies that were planted upon or near to the 

 place where diseased trees have been removed, showed on examination, the presence 

 of a mycelium within them but not in sufficient quantities to cause their death. 

 This indicates that infection can take place through mycelium. 



It would appear to be probable that the disease may spread : — 



(1) By mycelium through the soil from root to root. 



(2) By spores blown from tree to tree. 



(3) By germinating tubes of spores from petioles attacking either the roots 

 of the same tree or the roots of another. 



(4) By germinating " chlamydospores " from decaying petioles. 



The best conditions for the germination of the spores depend upon the 

 presence of suitable quantities of air and moisture, and the spread of the disease 

 would be expected to be most rapid when the conditions are the most favourable. 

 The distribution of fungus spores by wind and rain will be dealt with more fully 

 under the leaf disease and, therefore, will not be discussed here. 



The spread of mycelium in the soil depends a good deal upon the cultivation. 

 Any condition of the soil that is unfavourable to the coconut may favour the root 

 disease by hindering free root development. Excessive moisture and excessive 

 drought may be favouring conditions for the disease. The latter cannot be re- 

 medied except by irrigation, and does not appear to be a factor of any importance 

 in this disease. The former, excessive moisture, is noticeable in many of the low- 

 lying portions of the States. In these hollows, the soil is often of a clayey nature- 

 impervious to water— and, therefore, many of the air spaces between the soil parti- 

 cles are replaced by water. The normal working and growth of the root i9 

 interfered with, and the destruction of such roots by fungal mycelium may speedily 

 follow. The effects of excessive moisture can be lessened by careful attention to 

 drainage and to the mechanical condition of the soil. 



