RASPBERRY DISEASES IN MINNESOTA. 



237 



of insect pests and plant diseases causes a high percentage of 

 the reduction in quantity and quality of the fruit produced. 

 The following diseases are the most important in Minnesota, 

 Gray Bark, or Spur Blight. This is a fungous disease popu- 

 larly so named because of the visible external effects on canes and 

 spurs. I class it of first importance because of its widespread 

 occurrence, the extent of the damage and, until recently, the 

 slight attention that it has attracted. 



The Hopkins, Long Lake, Maple Plain and Excelsior dis- 

 tricts, in Hennepin county, are all infested, some fields show- 

 ing as high as 100% of the canes diseased. The districts about 

 Mankato, Bay Lake and Aitkin are all suffering from the de- 



Gray bark, or spur blight, of red raspberries. 



structive effects of this disease. It has been reported from 

 Douglas, Pine, Wabasha, Mower, Washington, Renville, Ram- 

 sey and Cottonwood counties as well. 



Not only has the reduction in yield been great in the last 

 few years, but in many places the effects are so marked that 

 the growers are seriously considering the abandoning of pres- 

 ent plantings altogether. 



Some growers believe gray bark to be most severe in older 

 plantings or on canes weakened by winter injury. There has 

 not been enough opportunity to collect conclusive evidence on 

 this and other points under our conditions. The effect of winter- 

 killing on various varieties, and the susceptibility of these same 

 varieties to disease, must be investigated. Correspondence on 

 this point with the Experiment Station will doubtless be of 

 mutual benefit to grower and investigator. 



The first appearance of the disease, early in July, is char- 

 acterized by bluish or brownish patches, either at the base of 



