CHAPTER XVI 



STEM AND LEAF DISEASES 



Pink Disease. 



This is a disease in which twigs and small branches appear as if 

 they had been dusted over with pink powder, and sustain damage 

 which commonly leads to their defoliation and death. In the 

 later stages the pink colour fades to grey, and the thin coating 

 cracks irregularly. In some cases the fungus assumes the form of 

 white or pink pustules arranged more or less in lines parallel with 

 the branches. 



West Indian records show that pink disease occurs in Porto 

 Rico, Dominica, St. Lucia and Trinidad on cacao, and has been 

 also seen on lime, grapefruit, pigeon pea, oleander and Amherstia. 

 The fungus to which it is due has been found to be identical 

 with that of the pink disease of the Eastern Tropics, which has a 

 very wide range of hosts and gives serious trouble in rubber 

 plantations. 



That the disease has not assumed anything like the same 

 importance in the West Indies would appear to be due to difference 

 in climate. The fungus is dependent on a very considerable 

 amount of humidity for vigorous growth. In even the wettest of 

 these islands there are few places opened up to cultivation which 

 are not penetrated more or less by wind and sun all the year 

 round ; it is notable that the disease on the lime in Dominica 

 is still known to exist only in one specially wet and sheltered 

 district, although it was recorded from the same place nearly 

 twenty years ago. On cacao in Dominica and St. Lucia the 

 disease has been known the same length of time and remains a 

 rarity. In Trinidad, according to J. B. Rorer, it has been found 

 on cacao only at rare intervals in the northern and eastern 

 districts and has not proved a serious trouble. 



Causation. 



The causative fungus Corticium salmonicolor B. et Br. (C. 

 javanicum Zimm.) was referred to for several years in West 

 Indian publications as C lilacino-fuscum B. et C., owing to a 

 mistaken identification by Massee of material from Dominica. 

 The infection probably comes in the first place from some forest 

 plant. The spores germinate on healthy bark and develop 

 a superficial mycelium of cobweb-like texture. The fungus later 

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