VI 



TEA 173 



Thread Blight or Wither Blight. This disease is 

 caused by Stilbum nanum, Massee, and is one of the 

 most destructive of the diseases of the tea. It kills the 

 branches and frequently the entire tree. It is due to 

 the fungus which grows both internally and externally. 

 Internally it is at first most abundant in the cambium, 

 but later passes inward to the tracheary tissues, causing 

 the wood to turn brown. The mycelia also grow out- 

 ward through the bark and spread over the surface, 

 forming a sterile, felted mass which is most abundant 

 on the under side of the branches and leaves. Near 

 the margin of these patches it breaks up into irregular 

 branched slender strands, many of them not thicker 

 than a common thread. It is these small threads that 

 pass to the leaves, forming a very delicate pattern. 

 The fungus rarely forms fruit, and then only on old 

 rotten branches which have fallen to the ground. The 

 fruit is in the form of small pin-like structures of a pale 

 yellow colour ; they are numerous and very small, and 

 give the appearance of a velvety or hairy mass. Since 

 it produces only conidia spores, it is possible that it 

 may be the conidial stage of some higher fungus. It is 

 probable that this fungus, like many others, travels 

 underground from plant to plant, and enters the host 

 through the roots. It is quite common and destructive 

 in India. This disease also attacks the mango, the 

 sapodilla plum (Acleras sapota), and many other plants, 

 both cultivated and wild. The diseased parts should be 

 cut and burned ; trenches may be dug and limed to 

 prevent the underground spread of the fungus. The 

 use of Bordeaux mixture is also said to have given 

 good results in checking the fungus. 



Copper Blight. This disease, which is due to Laestadia 

 tlieae, has been reported from India. It attacks the older 

 leaves, causing irregular copper-coloured spots on the 

 upper surface which finally cover the entire leaf, and give 

 a copper colour to both surfaces. In its advanced stages, 

 the pycnidia appear as very small black spots. Kemoval 

 and burning of diseased leaves and spraying with 



