552 GROWING BUSH FRUITS 



An affected plant never recovers and parts taken for propaga- 

 tion are also diseased. 



In red varieties the disease appears as a mottling and 

 puckering of the leaves and dwarfing of the canes (Fig. 235) ; 

 in black varieties the growing tips and young leaves are also 

 killed. Plants of red and purple varieties are seldom killed 

 outright, but the yield and quality are greatly reduced. Black 

 raspberries are frequently killed. The diseases, which are car- 

 ried by aphids or plant lice, 

 are disseminated chiefly by 

 winged forms and ants. They 

 may also be carried on till- 

 age implements. The streak 

 or blue stem of black and 

 purple raspberries is one of 

 the virus diseases. Some 

 varieties are resistant to the 

 virus diseases; others are 

 very susceptible. Cuthbert, 

 June, Marlboro, Ranere, Co- 

 lumbian, and Cumberland 

 are susceptible. Herbert, 

 Latham^ and Plum Farmer 

 are less so, at least under 

 many conditions. 



Plant resistant varieties 

 or those from disease-free 

 fields. Use ''certified'^ stock, that is, stock that has been rogued, 

 and kept free as attested by competent plant disease inspectors 

 representing a public agency. In some sections it will pay to 

 eliminate or rogue the diseased plants during at least the first 

 two years of the plantation. Take up the affected plants and 

 remove at once. Do not leave them in the rows or about the 

 field as the aphids will desert them for other plants as soon 

 as they begin to wilt. Plant the rows far enough apart so that 

 horses and tools do not brush the plants in tillage operations. 



{W, B. Rankin) 



Fig. 235. The red raspberry plant on 

 the left shows typical mosaic symp- 

 toms; the one on the right is normal. 



