CITEUS DISEASES. 



95 



cett ' that melanose is more serious in the more northerly citrus dis- 

 tricts of Florida, decreasing to the south, and practically lacking 

 in Cuba. For this reason it will probably never assume any im- 

 portance in Porto Rico. 



Melanose is a disease of the fruit, leaves, and young twigs. It is 

 characterized b}^ numerous, very small (seldom over one-sixteenth 



of an inch in diameter), raised 

 corky areas, yellow to deep 

 brown in color, and often de- 

 scribed as having the appear- 

 ance of masses of burnt sugar- 

 j These corky projections are su- 

 perficial only, never penetrating 

 the inner tissues of the organ at- 

 tacked. They may be scattered 

 irregularly, oi- in the case of the 

 fj'uit. be arranged in lines or 

 partial circles. They have the 

 additional characteristic on the 

 fruit of being encircled by a 

 break in the epiderm, giving a 

 scaly appearance. Melanose-affected fruits have a russeted appear- 

 ance and feel rougli to the touch. 



Leaves and twigs are subject to attack only while very young 

 and before they have hardened. The fruit is susceptible until prac- 

 tically mature. 



Melanose is due to surface infection by the spores of a fungus 

 known as Pliomopsis citri. Tt develops in dead twigs, producing 

 very minute, black, immersed fruiting bodies, and the spores are 

 carried by rain or other agencies to the new growth. The melanose 

 riiarkings themselves contain very little fungus growth and never 

 produce spores. 



In Florida the same fungus causes a rot in the mature fruit. 

 almost exactly similar in outward appearances to the stem-end rot 

 of Porto Rico, but this phase has not been noted here. 



The disease can be satisfactorily controlled under local condi- 

 tions by pruning out all dead wood. If at any time the disease should 

 become more serious, a spraying schedule can be outlined for liold- 

 ing it in check. 



Fig. 35. — Melanose markings on orange 

 leaves. 



' Bui. 262, Cal. Ex. St; 



