BLACKBERRY DISEASES 



167 



But the successive activities of Septoria Rubi have not been care- 

 fully studied ; this is probably due to the fact that the disease 

 which it produces has never been of great economic importance. 



The mycelium of the fungus growing in local areas within the 

 leaf-tissues causes the color changes and finally their death. 

 The fungus forms fruit- 

 ing bodies pycnidia 

 just beneath the upper 

 surface of the cuticle. 

 These, as they mature, 

 break through the cuti- 

 cle and stand exposed 

 over the affected area. 

 Within the pycnidia 

 spores are developed 

 which at maturity, under 

 moist weather condi- 

 tions, ooze out and are 

 scattered to other leaves. 

 Here they germinate in 

 water and the result is 

 a germtube which in 

 some way gets into the 

 leaf-tissues. A spot is 



the outcome. Little is known of the winter condition and 

 of the manner in which the first infections in the spring are 

 brought about. 



Control. 



In cases in which the leaf-spot disease becomes a menace it 

 may be kept in check fairly well by the use of bordeaux mixture, 

 4-5-50, or lime-sulfur 1-50. The spray should be applied as 

 follows :. (1) shortly after the leaf-buds unfold, (2) subsequent 

 applications at intervals of two to three weeks until the fruit is 

 about two-thirds grown. 



FIG. 46. Blackberry leaf-spot. 



