DISEASES OF COTTON 275 



though the indications are that when once the disease has made 

 its appearance it is hable to recur on the lower bolls under cir- 

 cumstances less extreme than are needed to induce the iirst 

 attacks. 



Mode of Infection. 



Nothing is known as to the carrying over of the fungus 

 from year to year, but the assumption is made that, as in other 

 members of the group, resting spores are retained in the soil. 

 The means by which infection is conveyed from boll to boll 

 have not yet been studied, but may be assumed to be the same as 

 in other Phytophthora diseases (p. 21). 



Resistance. 



S. C. Harland reports that the Montserrat strain H23, when 

 introduced in 1919 into the wetter climate of St. Vincent, proved 

 so highly susceptible that practically all the bolls were destroyed. 

 Another Montserrat strain D.i. was more resistant under the 

 same conditions, approaching nearer in this respect to the ordinary 

 St. Vincent strains, and gave a fair crop. The St. Vincent 

 strains A.B. and A.N., developed from the Superfine type, show 

 considerable resistance to soft-rot as well as to the angular spot 

 disease. 



No type has been found sufficiently resistant to avoid loss of 

 the lower bolls in wet weather, the difference being expressed in 

 the survival of the bolls on the upper parts of the plant. 



The control of soft-rot by spraying with Bordeaux or Burgundy 

 mixture has not yet been sufficiently tested. No cases occurred in 

 the sprayed plots in St. Vincent in 1918-19, while a fair number 

 appeared on the unsprayed plots. It may be possible to show, 

 when an opportunity occurs, that spraying at the outset of a 

 threatened epidemic can arrest the progress of the disease, 

 which at such times is liable to destroy most of the visible crop 

 of bolls. 



DiPLODiA Boll Rot. 

 History and Distribution. 



The existence of a species of Diplodia on cotton bolls has been 

 several times recorded in the United States since M. C. Cooke 

 described Diplodia gossypina from Indian material in 1879. C. 

 W. Edgerton, in 1912, seems to have been the first to attribute a 

 definite boll disease to its agency. He reports that considerable 

 loss from this cause occurs throughout the State of Louisiana, 

 averaging perhaps 2 per cent, on the whole crop, but occasionally 

 in small areas reaching 10 per cent. The present writer has long 

 been familiar with the envelopment of rotted West Indian Sea 

 Island bolls with masses of black Diplodia spores, but only in 



