BLACK ROT OF GRAPES 
The black rot is an American disease, known as a destructive malady 
in our vineyards for nearly a century before its appearance in Europe in 
1885. It is markedly epiphytotic in its occurrence on cultivated grapes. 
SYMPTOMS 
All green parts of the vine, including the young canes, may exhibit 
lesions of the black rot. Old woody parts are never affected. 
On the leaves. Spots on the leaves are reddish brown and more or 
less circular. The spot at first appears as a small blanched area. The 
spread is concentric but not perfectly circular. Study the material 
before you and OBSERVE :— 
1. The size and distribution of the lesions over the surface of the 
leaf. Note the color. 
2. The shape of single spots and their relation to the finer vein- 
lets. Study the margin closely; even or crenulate? 
3. That certain spots show minute black bodies,—structures of 
the pathogene. Are they superficial or sunken in the leaf-tissue? What is 
their arrangement on the lesion? On which surface are they found? 
Make such SKETCHES as are necessary to bring out the character of the 
spots on the leaves available. (See photograph 1.) 
On the berries. The first signs of the disease on the berries are not 
readily detected except by careful observation. The lesions rapidly 
become apparent, however. Study the diseased berries provided. oB- 
SERVE :-— 
4. The different stages in the development of the lesion from a 
small blanched or brown discoloration to the black and shriveled mummy. 
(See photographs 2 and 3.) 
5. The characteristic black fruit-bodies in the lesion; position 
and arrangement. At what stage in the development of the lesion do 
they appear? (See photographs 3 and 4.) 
DRAW to show the development of the symptoms on the berry. 
On the canes and tendrils. In the material prévided, oBSERVE:— 
6. The character of the lesions. Compare and contrast, with 
those on the leaves; with those on the fruit. 
7. The extent of the lesion on the cane; on the tendril. Are 
the lesions limited and definite? Is there a tendency to girdle? 
8. The number of lesions; their form, size, and the presence of 
the black fruit-bodies of the pathogene. 
Study photograph 5, noting lesions on canes, petioles, midribs and 
tendrils. 
Make prawincs to illustrate these studies. 
ETIOLOGY 
The pyrenomycetous fungus, Guignardia Bidwellii (Ellis) Viala and 
Ravaz, is the cause of the black rot of grapes. Its conidial form has been 
given the genus name Phyllosticta, when occurring on the leaves but when 
on the canes, Phoma. A variety of specific names have been applied. 
to it. (See Cornell Bul. 293:307.) 
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