BLACKBERRY DISEASES 163 



infected, show little external indication of disease. It has been 

 observed that affected plants are freer from prickles than normal 

 plants. Healthy and diseased canes may be found in the same 

 stool. All affected canes should be destroyed. The same dis- 

 ease also occurs on raspberries (see fuller discussion, page 399). 



DOUBLE-BLOSSOM 

 Caused by Fusarium Rubi Winter 



This is primarily a disease of the dewberry, although the cul- 

 tivated blackberry is affected. The trouble occurs to some ex- 

 tent on the high-bush blackberry. Among the dewberries the 

 Lucretia and Rathbone are notably susceptible, while the Black 

 Diamond and other varieties are less liable to attack. 



Double-blossom is most common in the Delaware-Maryland 

 peninsula. It has been observed, however, in Illinois, Tennessee, 

 Texas, New Jersey, North Carolina and Alabama. The first 

 record of the disease comes from Illinois about 1885, although 

 the important writings on the subject of double-blossom are 

 recent. 



The history of the disease shows that it does not vary in 

 abundance in a given region from year to year. But, as would 

 be expected, it continues to increase in severity until affected 

 plants are worthless. If diseased plants are allowed to go un- 

 treated, their life is shortened by two or more years. In the 

 Delaware-Maryland peninsula double-blossom has been so se- 

 vere on Lucretias that half of the growers have discontinued 

 dewberry culture. 



Symptoms. 



Evidences of double-blossom appear early in the spring just 

 as the leaf-buds are opening. The trouble may be detected 

 previous to this by the enlargement of the diseased buds. When 

 affected leaf-buds open there is produced, in place of normal 

 leaves and shoots, a witches'-broom. This abnormal develop- 



