186 DISEASES OF ECONOMIC PLANTS 



spots, with well-defined margins, characterize this disease. 

 The bark cracks and forms scales. The spots are at first 

 scattered, but in time coalesce and form large areas upon the 

 larger branches and trunk, giving it a scaly appearance. 



Sweet oranges are most affected, the fruit ripening 

 prematurely. It is claimed by Fawcett ^ that the disease 

 may be due to the wither-tip fungus. 



Top working is recommended, also heading back and 

 painting the trunk and the stumps of the branches with 

 carbolineum, one part to one part of water. 



Gum disease. — Several diseases recognized by the exuda- 

 tion of gum from the trunks and branches of the trees are 

 called '' gum diseases." Their causes are not definitely 

 known; by some they are attributed to mechanical injury 

 alone; by others to poor cultivation or water injury in ir- 

 rigation ; by others to the presence of soil around the trunk. 



Sooty mold (Meliola Camelliae (Catt.) Sacc.). — Sooty 

 mold has been known in Florida for twenty or twenty- 

 five years, but was at first considered to be of but little 

 import, though it is now regarded as injurious to both fruit 

 and trees. The disease covers the fruit and leaves with 

 a black, velvety, membranous coating which may be stripped 

 from the leaves. 



As the disease follows certain insects that exude a honey- 

 dew, it may be successfully combated by destroying these 

 insects. Fumigation or thorough spraying with a resin 

 wash or kerosene emulsion is recommended. 



Blue mold (Penicillium italicum (Wehm.), and Penidllium 

 digitatnm. (Fr.) Sacc). — This decay of citrus fruits in transit 

 from California causes a loss estimated at from $500,000 



1 Fawcett, H. S., Fla. Agr. Sta. Bui. 98, Mch. 1909. 



