i68 DISEASES OF CROP-PLANTS 



cost per 100 trees, with materials at pre-war prices, was about 

 $10 per application. An addition of nearly 7,000 pods per 

 1,000 trees, or 635 lb. dry cacao, has been obtained from sprayed 

 as compared with unsprayed trees. 



Van Hall has issued striking figures as to the success attained 

 in the direct treatment of canker on a large and badly infested 

 plantation of Criollo in Java. The practice of deep excision and 

 treatment with carbolineum and tar having failed to arrest 

 the losses, a change was made to a policy comprising (a) reduction 

 of the heavy canopy by thorough pruning ; {b) treatment of the 

 cankers by merely shaving off the outer bark to allow the infested 

 tissues to dry out, the use of tar being avoided as preventing 

 this consummation ; and (c) the more careful control of boring 

 beetles, the tunnels of which afford openings for infection. 

 By these means the number of trees attacked was reduced from 

 4,400 in the first to 318 in the third year, and the annual loss 

 of trees from 5.4 to 0.7 per cent. 



Rorer has pointed out that the collection and destruction 

 of diseased pods, on which a good deal of stress has been laid as 

 a sanitary measure, cannot be held to have much effect on the 

 prevalence of this disease, and has been given up as unremunera- 

 tive by planters who have tried it. There is an early and enor- 

 mous production of spores from the affected pods while they are 

 on the tree which is quite sufficient to maintain an epidemic, 

 and the only feasible means of prevention during its continuance 

 is the protection of the healthy pods by spraying. On fallen pods 

 and husks the parasite seems unable to maintain itself against 

 the competition of numerous fungi more efficient as saprophytes. 

 In this respect it differs from Diplodia. It should be noted 

 however in this connection that marked infestations often exist 

 on the trees in the neighbourhood of the sites to which the pods 

 are brought to be broken. 



The Surinam Witch-Broom Disease. 



The principal feature of this disease is the hypertrophy of 

 young shoots, which assume a monstrous form and shortly die. 

 To this feature are also added (i) the production of hardened 

 (indurated) and malformed pods, which either fail to come to 

 maturity or have a part of their contents spoiled, and (2) star- 

 blooms, which are crowded blossoms developed on hypertrophied 

 cushions and usually resulting only in a few misshapen pods. 



History and Distribution. 



The disease was first reported in the Saramacca district of 

 Surinam, about 1895. It spread by degrees through the colony 

 and caused an enormous amount of damage. The average 

 annual export of cacao for the 5 years 1893-7 was 3^ million 

 kilos, that for the five years igo8-i2 was reduced to i^ million. 



