104 Diseases of Economic Plants 



Crown-gall {Pseudomonas tumcfaciens). — Frequently 

 swellings are noticed on the stems near the roots, or even on 

 the higher parts of stems, of the raspberry or blackberry 

 sufficiently numerous to injure the health of the plant. 

 These galls are apparently of the same nature as the crown- 

 gall of the peach, almond, apple, etc. It is desirable to 

 pull up and destroy diseased plants and avoid placing black- 

 berries and raspberries on ground which is known to be 

 infected. 



Leaf-spot (Septoria ruhi West.).- — Upon the leaves of 

 blackberries, raspberries, and dewberries small spots fre- 

 quently appear, having a central region white or ashen in 

 color, and the border brown or often of reddish tint. These 

 spots are about 3 mm. in diameter. Close examination of 

 the central, ashen area, especially with a hand lens, reveals 

 exceedingly small, black pycnidia scattered throughout. 



While this disease is exceedingly common and of wide 

 distribution, it does not often develop an epidemic and usually 

 does but little injury, though its damage has been estimated 

 as high as 20 per cent in Florida and Ohio. No treatment 

 has yet proved of sufficient value to warrant its use. 

 - Orange-rust ^-^ (Gijmnoconia inter stitialis (Schlecht) 

 Lager.). — In the early spring the under sides of the leaves 

 of blackberries and raspberries often present a livid red or 

 orange color. This rust was observed as early as 1817, in 

 Kamchatka, and is very widely distributed in the LTnited 

 States, Europe, and Asia, upon some nine species of Rubus, 

 both cultivated and wild. It is known from Maine to 

 Minnesota and Florida to California, and is in some cases 

 very destructive. 



Examination of a diseased plant shows that its growth 

 has been much retarded by the fungus; the leaves are curled, 

 distorted, unusually small, and lacking in green color. Plants 

 so affected never recover, and are useless. Preceding by 

 some two or three weeks the conspicuous red rust, above 

 referred to, occurs another stage of the disease that is often 

 overlooked. This consists of a thick growth of small colum- 



