GRAPE DISEASES 



255 



the Delaware variety. The Pocklington, although not exten- 

 sively grown, is apparently most susceptible. 



The disease appears to be of American origin, and there is 

 little doubt but that it is still confined to this country. It 

 was unknown until 1909, when its prevalence and cause were 

 discovered. Losses from dead-arm are estimated at 1 to 

 5 per cent annually for New York vineyards, while the total 

 for all states concerned is unquestionably of considerable im- 

 portance. 



Symptoms. 



The arms, trunks, green shoots, petioles, peduncles, leaf- 

 veins and fruits are affected. As the name indicates, the disease 

 exhibits itself chiefly through the death of the arms (Fig. 67). 

 Frequently, however, the whole vine dies, in which case suckers 

 usually grow up at the base. The affected vines may die at any 



FIG. 67. Dead-arm of the grape-vine, general appearance. 



