210 DISEASES OF CROP-PLANTS 



Grey Blight. 



A fungus identified by G. Massee as Thelephora pedicellata, 

 Schwein, now placed in the genus Septobasidium, forms a dense 

 slightly raised layer of felted mycelium, slaty-grey when fresh, 

 changing to brownish grey, on leaves and twigs of lime in St. 

 Lucia, Dominica, and Montserrat. The same or a very similar 

 fungus has been seen in large patches on pigeon pea stems in 

 St. Vincent and Trinidad. S. Langloisii Pat., which may very 

 well be the species above referred to, is recorded by E. A. Burt 

 from Grenada. A brown species occurs in Dominica. 



According to T. Petch, the genus Septobasidium, made up 

 of species all of similar encrusting habit, is parasitic on scale 

 insects, and this is so far borne out by local experience that the 

 fungus is found in association with colonies of purple scale on lime, 

 and mass infestations of a white scale (Chionaspis ?) on pigeon 

 pea. In the former case the mycelium has been found growing 

 under the scale and attacking the body of the insect. 



An effect which may be accidental but is none the less real 

 is sometimes produced on the enveloped twigs and small branches 

 of lime. There is a free production of gum from raised swellings 

 where the bark is covered by the fungus, and this in a number of 

 cases seen has resulted in the death of the portion of the branch 

 lying beyond the invested part. 



No evidence of penetration has been found, and the most 

 probable explanation of the effect is that it is due to suffocation. 

 It has no serious importance. 



Leaf Spots, 



Brown patches extending from the tip or margin of the leaf, 

 or smaller spots, occur occasionally, and are infested with Col- 

 letotrichum glceosporioides. (See Citrus Anthracnose). 



Roundish raised spots, foxy red or black, caused by Cephal- 

 euros mycoidea are common in some localities. (See Algal 

 Disease, p. 152). 



Citrus Trees in General. 



Citrus Anthracnose. 

 A position of some uncertainty exists with regard to the extent 

 of the parasitism of the very generally distributed fungus Colleto- 

 trichtim gloeosporioides on citrus trees. It has been widely 

 regarded in the United States and some parts of the West Indies 

 as the cause of wither-tip, spotting and streaking of fruit, and 

 spotting of leaves on citrus trees generally. With the separation 

 from it of the active parasite Glaosporium limetticolum (see 

 Anthracnose of Limes) which has been shown to be responsible 

 for the blossom blight, wither-tip, and fruit canker of limes. 



