DISEASES OF COCONUT 193 



DiEBACK. 



In Jamaica the pinnae of the older leaves die back succes- 

 sively from the tips and the crown of the tree may be reduced 

 slowly or rapidly to a few expanding leaves. The name dieback 

 has been given to this affection and a Diplodia is in most cases 

 found fruiting behind the advance margin of the dead zone. 

 This affection is regarded by Ashby as primarily a root deteriora- 

 tion, possibly of the same kind as those reported recently on cane 

 and other crops in Hawaii and on cane in Porto Rico, 



Leaf Blight. 



A condition of the leaves in which they prematurely take 

 on a more or less general yellow colour, while the individual 

 leaflets have yellow, brown, or grey patches scattered over them 

 and dead areas at their tips and along their margins, may be 

 designated by this name. Such a condition arises from un- 

 suitable cultural conditions, of which lack of drainage is perhaps 

 the most common, but packed soil, root competition with other 

 plants, and undue exposure under conditions of low rainfall and 

 absence of available subsoil water will produce it. 



Usually the condition is accompanied, and in the immediate 

 sense caused, by infestation with scale insects and weakly para- 

 sitic fungi. It is on old and failing leaves, and on younger leaves 

 in a condition of debility that Pestalozzia palmarum Cke. has 

 been commonly observed in the West Indies. This fungus has 

 been reported from Java as being on occasion a serious leaf- 

 parasite on newly planted trees. Fetch has stated that in Ceylon 

 it occurs as a rule on old leaves and does no appreciable harm, 

 and that its appearance on younger leaves is a sign that something 

 is wrong with the conditions and should be met by manuring. 



The fungus is found in yellow or brown oval spots which come 

 to have a diameter of a centimetre or more, and dry up in the 

 centre. The conidia are formed in pustules on both sides of the 

 leaf. Each has 5 cells, of which the 3 median ones are brown 

 with thicker walls. The terminal cells are hyaline, the superior 

 one bearing 3 threadlike appendages and the inferior one being 

 prolonged by a portion of the slender conidiophore. 



A Diplodia, D. epicocos Cke. is also found occupying dried-out 

 spots on the leaves, and has been recorded from Jamaica, Trini- 

 dad and British Guiana. Its pathogenic relations are not 

 established. 



