FUNGI IMPERFECTI 327 



Control. Adequate methods of control have not been devel- 

 oped. It is important, however, to select varieties which permit 

 the access of light to the bolls. Seed selection from healthy bolls 

 may prove of value. 



XXVIII. WITHER-TIP AND SPOT OF CITRUS FRUITS 



Colletotrichum Glxosporioides Penz. 



Rolfs, P. H. Wither-Tip and Other Diseases of Citrus Trees and Fruits. 

 Bureau Plant Ind., U. S. Dept. Agl. Built. 52: 1-20. ph. 1-6. 1904. 



Host relations.. In practically all parts of the world in which the 

 orange and other citrus fruits are cultivated this fungus is more 

 or less common. The diseases or injuries produced by it are vari- 

 ously known as wither-tip, leaf spot, anthracnose, canker, and lemon 

 spot, depending upon the effects upon the host. The fungus is a 

 far more active parasite in humid regions, and in Florida, particu- 

 larly, the disease appears to be growing in importance from year 

 to year. In 1891 it was casually noted by Underwood, and since 

 that time it has rapidly come into prominence as a destructive 

 agent to the citrus industries. 



On orange. The wither-tip effect is particularly characteristic of 

 orange trees. It may be found upon trees of all ages, affecting and 

 killing back the tips of the branches. On large trees this neces- 

 sarily prevents the setting of a heavy crop of fruit. The varieties 

 of the orange seem to be about equally affected. The disease is 

 easily distinguished from dieback (a disease not associated with 

 a specific organism) by unmistakable characters, especially by the 

 ashen color of the twigs where dieback effects are brown ; by 

 the line or ring separating injured from healthy tissue, which is 

 absent in the other disease ; by the absence of any resinous de- 

 posit; and by the frost-like killing of twigs, where in dieback 

 twisted branches and the development of twigs with brown-stained 

 bark are common. 



On lemon. Upon the lemon it causes not only a wither-tip, but 

 also a very definite leaf spot, and from the diseased areas of the 

 leaf the fungus may extend into the twigs, thus resulting in the 

 wither-tip, the more acute form of the trouble. The mature fruit 

 may also be affected in the form of a fruit spot. It would appear 



