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 Fie. 46. — Blackberry leaf-spot. 
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, 
45-50, 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. 
