MYCOLOGICAL SECTION. 99 



face assume a brownish hue, which gradually becomes more intense, 

 finally having all the characters of completely dried and dead tissue. 

 These spots may be quite small. Late in the season the older leaves 

 attacked are often covered all over with minute brown spots, which 

 are usually sharply defined, being limited by the nerves in the leaf ; 

 again, they may be so large as to nearly cover the whole surface, in 

 which case the destruction of the leaf is quickly accomplished. 

 Under the final action of the fungus the leaf becomes thoroughly 

 dried and shriveled, as if burned, and the tissues are particularly 

 brittle. It very rarely occurs that the mildew itself appears on the 

 upjDer surface of the leaf. 



On the shoots. — In severe cases the fungus extends to the young 

 shoots, and, although the conidia-bearing filiaments do not appear 

 excepting upon the youngest and most tender of these, the action of 

 the mycelium checks their further development, and finally the tis- 

 sues are killed. The effect upon the shoots is often to produce dark- 

 colored, slightly depressed markings as a consequence of the sinking 

 away of the tissues beneath. These markings are quite distinct from 

 the deep and lacerated lesions of Anthracnose. 



On the berries. — Berries when attacked early by the Peronospora 

 rarely attain more than one-fourth their full size, often remaining no 

 larger than small peas. They soon turn brown, or, when the fungus 

 fruits upon them, gray in color. There is thus produced a kindof 

 "rot," which is popularly named ''brown rot," or "gray rot." 



The berries of some of the varieties of grapes cultivated on the 

 Department grounds were severely infested with the Downy Mildew 

 last sumnier (1886). In some instances the peduncle was much swol- 

 len and distorted through the action of the mycelial growth within, 

 and the fructiferoiis filaments or conidiophores of the Peronospora 

 whitened here and there with a downy coating, the berries as well 

 as the stalks supporting them. 



REMEDIES. 



Since the appearance of the Downy Mildew in France, in 1878, its 

 ravages have increased in that country and extended throughout 

 the grape-growing regions of Central and Southern Europe to such 

 an alarming extent as to call for the exercise of every effort on the 

 part of individuals and Governments to check or destroy it. Ex- 

 perments with remedies and preventives, begun in 1882, have been 

 continued systematically in European vineyards, and the results 

 obtained in 1885* were so satisfactory, that you considered them worthy 

 of trial in this country, and for this purpose distributed last May the 

 following circular to parties thought most likely to be interested in 

 the subject: 



U. S. DEPARTMENT OF AGRICULTURE. 



Treatment of the Downy Grape Mildew {Peronospora viticola) and the Black-Rot 



{PJioma uvicola). 



In view of the fact that Mildew and Black-Rot have been so destructive to the vine 

 in this country that in some sections grape culuire has become unprofitable and for 

 this reason many are abandoning the business, the importance of making special 

 efforts to discover effective remedies for these diseases will not be questioned. 



With this object in view, the remedies which have recently been employed in 



* For a detailed account of the use of these remedies in France and Italy in 1885, see 

 special bulletin No. 2, Botanical Division, on the ' ' Fungus Diseases of the Grape- Vine. " 



