100 VEGETABLE PARASITES AND EPIPHYTES 



" Diplodia cacaoicola {Thyridaria tarda) was described 

 by Hennings in 1896 on the wood of the cacao plant from 

 Kamerun. It has since then been shown to occur in 

 Tropical America (including the West Indies), Java, 

 Samoa, Ceylon, the Philippines, and San Thome. It ranks 

 among the most injurious of the pests of cacao and also 

 possesses the widest area of geographical distribution. 



" The fungus attacks the stem and fruits of the cacao 

 plant. On the stem the disease is popularly known as 

 ' die-back.' The young shoots first show symptoms of 

 disease ; they commence to die at their tips and proceed 

 to die back toward their bases ; if the disease is allowed 

 to proceed unchecked the older branches and finally the 

 trunk usually become affected. In some cases the growth 

 of the fungus has been known to be limited to a definite 

 area on the trunk or on a branch ; it then produces a 

 canker-like spot on this area. 



" On the fruits the disease is known as ' brown-pod ' ; it 

 makes its appearance in the form of a discoloration at 

 one or other end of the fruit. The discoloured area 

 extends until the whole, or nearly the whole surface 

 of the pod becomes dark brown in colour. The fungus 

 spreads through the tissues of the ' shell ' to the mucila- 

 ginous coat surrounding the beans and finally attacks 

 the beans themselves. 



" The fungus can only effect an entrance into the stem 

 through a wound ; in the case of the fruit, however, it 

 appears to be capable of entering through the unwounded 

 basal or stigmatic ends. All wounds made on the stem 

 by pruning, or such as have arisen from other causes, 

 should be sealed with coal-tar or with a mixture of coal- 

 tar and clay. Care should be taken not to confuse the 

 disease caused by Diplodia (Thyridaria) with the dying 

 off of the tips of young shoots which commonly occurs on 

 cacao plantations from drought, want of shade, etc. 

 Diseased shoots should be cut off at a distance of 6 in. to 

 1 ft. from the nearest dead end ; diseased fruits should be 

 removed from the tree. All diseased material should be 

 buried in pits with lime. A vigorous growth of the plant 

 induced by good sub-soil drainage, green manuring, and 

 careful pruning has been shown to render it less liable to 

 attack. Spraying of the fruits with ' Bordeaux Mixture ' 

 has yielded good results in some countries. Spraying 



