84 KEPOKT OF THE COMMISSIONER OF AGRICULTURE. 



be made by potato-growers tban leaving dead stems, leaves, and tubers about their 

 fields, especially after a potato crop has suffered from disease. * * * With the ob- 

 ject of prevention in view, hardj'^ varieties wliieli liave not exhibited the disease siionld 

 be selected and reselected. They should be grown where possible in well-draiucd, dry 

 soil, and mineral manure should be used. As darkness, heat, and humidity arc highly 

 favorable to the growth of the Peronospora, all potatoes should be stored in perfectly 

 dry, airy jdaces in positions where light is not entirely excluded. 



The grape-vine Diildcw, which has doue so much injury to the grape- 

 vine in this country, and luore recently to the vines of Europe, is caused 

 by Ferono.sjiora viticoJa. The action of this fungus is well known. It 

 generally shows itself upon the under surface of the leaf, where the 

 conidial spores are produced in great abundance. The winter spores 

 are developed upon the mycelium within the tissues of the leaf, where 

 they remain until spring. The ravages of this fungus are not conllned 

 to^'he foliage, but sometimes extend to the berries themselves, produc- 

 ing a species of rot. Prof. William Trelease, in discussing the various 

 causes of grape rot {see Transactions of the Wisconsin State Horticul- 

 tural Society, vol. xv, p. 196), says that the most destructive form of tbis 

 disease in Wisconsin is a direct result of the growth, in the berries, of 

 the fungus which causes the common leaf disease of the vine. The fun- 

 gus has been found growing with such luxuriance upon wild grapes in 

 iowa as to cover the whole plant with a white velvety gTOwth and so 

 aifecting the vine as to prevent its reaching more than a foot or so in 

 height.* 



The common Virginia creeper {Ampelopsis qninqvcfoHa) acts as a 

 host plant for Peronospora viticola, a fact recently discovered by Br. 

 Farlow and Professor Trelease. 



Writers having little knowledge of fungi have often confounded the 

 Peronospora of the vine with the mildew caused by Uncinula spiralis, 

 already referred to. The latter is confined chiefly to the upper surface 

 of the leaves, and as it is wholly a surface-growing fungus it is far less 

 injurious than the Peronospora, and is, moreover, less difficult to con- 

 tend with. 



Many remedies for the disease of the vine due to the Peronospora 

 have been proposed, but so far the most ellectual specific known is a 

 solution of lime and sulphate of copper. It is made by dissolving 18 

 pounds of sulphate of copper in about 22 gallons of water; in another 

 vessel mix 34 pounds of coarse lime with to 7 gallons of water, and to 

 this solution add the solution of copper. A bluish paste will be the re- 

 sult. This compound, when thoroughly mixed, is brushed over the leaves 

 of the vine with a small broom, care being taken not to touch the grapes. 

 This remedy, it is asserted, will not only destroy the mildew, but will 

 Xjrevent its attacks. 



Without going into a more detailed account of the diseases caused by 

 the Peronosporeo} at this time, we may simply add that onion m'old is dim 

 to the attacks of Peronospora sclileidcniana,] lettuce mold to Peronos- 

 pora gangliformis, the rose rot to Peronospora spar sa^X clover sickness or 

 the mildew of clover to Peronospora trifoUorum ; Peronospora nivca at- 

 tacks the parsnip and allied plants, and Peronospora parasitica is inju- 

 rious to turnips and cabbages as well as lettuce.§ Some of the species 

 here named mitigate somewhat the evil they do by infesting harmful 



* Dr. Halsted, iu Botanical Gazette, vol. x, p. 338. 



tFor an account of this disease of the onion, see first annual report of the Wiscon- 



SLu agricultural experiment station, pp. 36-44. 

 X See The Gardener's Monthly for July, ISdo. 

 $ See American Agriculturist, 1880, p. 148. 



