DISEASES DUE TO NON-PAEASITIC OR DOUBTFUL CAUSES. 



CHLOROSIS. 



Chlorosis of sugar-cane has been noted only in the southern and 

 southwestern portions of the Island, the irrigated sections. It is found 

 in varying degree of severity from cases with absolutely white leaves 

 through various shades of yellow to those in which the affected leaves 

 show only yellow stripes. Affected areas vary in size from a fraction 

 of an acre to several hundred acres. It has been especially noted 

 near Ponce, Yaueo, and Santa Isabel. 



Studies of the phenomenon from a chemical standpoint, have been 

 conducted by Mr. P. C. Gile, (33, 34) of the Mayagiiez Experiment 

 Station. He made a soil survey of affected spots, analyses of the 

 soils, and a series of experiments with manure and ferrous sulphate. 

 He ascertained that bleached cane occurred where the soil was exces- 

 sivel}^ calcareous, but that the real cause of the trouble lay in lack 

 of sufficient assimilated iron. Plants treated with a solution of ferrous 

 sulphate either when applied around the roots or painted on the 

 leaves, regained a normal green color. 



As a result, however, of the field experiments, the conclusion 

 was reached that while increased yields and a measure of control 

 were secured by applications of iron, the amount necessary made its 

 use on a practical scale, prohibitive. 



Field observations show the presence of fungi on chlorotic canes, 

 l)ut to the same extent as on normal cane, so that they have no direct 

 relation with the disease, nor do insects. Earle (21) observed chloro- 

 sis near Ponce, confusing it with root disease with which it was 

 associated. Chlorosis of sugar-cane has not been reported from other 

 countries. 



YELIiOW STRIPE. 



Yellow stripe is more or less of a chlorotic condition in which 

 tile chlorosis is restricted to stripes in the leaves. In Porto Rico 

 this has never been seen in more than isolated stools of a tield, with 

 the exception of those cases where it occurs in connection "sWth chlo- 

 rosis on the south side of the Island. 



In Java mucli lins been made of this disease, l)ut with no other 

 conclusion than that it was a physiological condition, varying with 

 the different varieties of cane. 



MOTTT;ING. 



About tw(i ycais ago thci'c was brouglit to the attention of the 

 junior author a situation in tlic cane fields of tlie Arecibo-Aguadilla 



228 



