POPULAR BULLETIN REPRINTS. 



PRUNING FAILS TO CONTROL A CURRANT DISEASE.* 



F. H. HALL. 



More than twenty years ago, a disease was 



An old, obscure discovered which has become today a very 



disease. destructive trouble in the currant plantations 



of the Hudson Valley. The cause of this 



disease remained long unknown ; but careful study by botanists 



of this Station and the Cornell Station proved it to be due to a 



fungus which has three distinct spore forms. Of these, the basal 



form is Botryosphoeria ribis, so that this stands as the scientific 



name of the fungus which causes currant blight, currant cane 



blight, or currant cane necrosis. Usually, the discovery of the 



cause of a disease soon leads to a remedy, but in this case no 



preventive or remedial treatment can yet be recommended. 



On certain canes, or portions of the canes, 

 Symptoms of the leaves wilt, turn brown and die. An 

 the disease. affected cane will show a section of dead 

 wood from one to four inches long where the 

 bark has been killed and wood and pith invaded by the mycelium 

 of the fungus. This hinders the ascent of sap and thereby causes 

 all the upper part of the plant to wither and die. The general 

 appearance is very similar to that caused by borers in the canes, 

 but when this insect is responsible, a distinct burrow will be found 

 and the larva, itself, may be present. In fungus-blighted canes, 

 neither burrow nor larva can be found, but on careful examina- 

 tion, especially with a microscope, fine, whitish, cobwebby threads 

 may be discovered in the discolored pith at the point of attack. 



This localization of the injury made it seem 

 An unsuccessful possible that summer pruning to remove the 

 remedy. diseased wood, with destruction of the affected 



portions, might check the progress of the 

 disease. Accordingly, two experiments with this apparently prom- 

 ising method of control were begun in the spring of 1907. Within 

 a year or two it was found that the method offered no chance of 

 success in an old plantation. However, the second test, begun 

 in a plantation only one year set, has now been continued for 

 six years, all canes showing signs of the disease being pruned out 



* Reprint of Popular Edition of Bulletin No. 357; see p. 143 for Bulletin. 



[725] 



