DISEASES OF LIME AND OTHER CITRUS TREES 215 



the green fruit, finally becoming dark. Trees heavily infested 

 have been successfully treated by heading back and spraying 

 with Bordeaux mixture. 



Scab. 

 Nature and Distribution. 



Citrus scab is an affection which produces corky raised areas 

 and warts on young growing leaves, fruits and sometimes twigs, 

 resulting commonly also in some deformation. In the tropical 

 and sub-tropical regions of the New World it occurs with great 

 frequency, in some districts quite regularly, on sour orange and 

 rough lemon. From these hosts, in common use as stocks, it 

 appears to have developed strains virulent to grape-fruit, and it 

 is in connection with the important business developed in Florida, 

 Cuba and Porto Rico for the supply of the American market 

 with this fruit that scab has assumed great importance. The 

 lemon industry, so far as it exists in the places mentioned, has 

 also been seriously affected by it. The sweet orange and most 

 of the mandarin group show little susceptibility to the disease 

 The lime is reported to be attacked in the Isle of Pines (Cuba) 

 and in Ceylon. In Porto Rico and in the Lesser Antilles this 

 host has not been noted as susceptible. 



The disease occurs on the sour orange in these islands, but 

 owing to the scattered distribution of its appropriate hosts and 

 their small commercial importance has received little attention. 



In addition to the localities already mentioned, scab of the 

 type under notice is recorded from Japan, Australia, and South 

 Africa. It fails to develop any virulence in the dry climate of 

 California. 



The disease is reported to have made its appearance in Florida 

 in 1884, and to have spread rapidly through that and the adjoining 

 States. It is conjectured to have been introduced from Japan. 



Appearance and Effects. 



It is advisable to describe the disease in some detail owing 

 to the liability to confusion between scab and canker. As 

 met with by the writer in these islands the affection has usually 

 consisted of small roundish raised corky spots on leaves and green 

 twigs. The following description quoted from J. A. Stevenson 

 refers to the more virulent form occurring in Porto Rico. 



" The first signs of infection are circular, minute, trans- 

 lucent areas followed by a rapid production of the corky out- 

 growths so characteristic of the disease. On the fruit these 

 corky outgrowths, wartlike in appearance, are produced, 

 and vary much in size and shape, often running together 

 or occurring in such numbers as to cover a large percentage 

 of the surface o^ the infected fruit. At times plateau-like 



