28 FIELD STUDIES OF THE CROWN-GALL OF THE GRAPE. 



SUMMARY AND RECOMMENDATIONS. 



The disease of grapes in this country designated as black-knot, 

 crown-knot, root-knot, crown-gall, and as root tumors has been 

 known for many years. In Europe it has been known for a longer 

 period as "Grind,'' "Kropf," "broussins," "rogna," " tuberculosi," etc. 



Two forms of the disease occur commonly on varieties of Vitis 

 vinifera in the southwestern and western United States. One form 

 occurring as rough, often hard, excrescences on the canes of grape- 

 vines is designated as cane galls in this bulletin and is also known as 

 "black-knot," "Grind," "broussins," "rogna," etc. (PL II, fig. 2.) 

 The other form, occurring at or below the surface of the ground on 

 the crowns and roots of the vines in the form of soft galls, is designated 

 as root galls in this paper, but is also known as "tumors," "Kropf," 

 "rogna," and "tuberculosi." (PL III, fig. 1.) 



The crown-gall, or a similar disease, is widely disseminated in many 

 parts of the world, especially where varieties of Vitis vinifera are 



grown. 



The entrance of the disease in vines is favored by injuries, such as 

 those due to freezing and late frosts, to priming, etc. The effect of 

 the disease is very destructive, often killing or stunting nearly all the 

 vines in a vineyard in a few years, resulting in a heavy loss in many 

 localities, especially in the western United States. 



The galls usually develop annually, rotting away at the end of the 

 growing season, the rot killing the adjacent tissues and cutting off 

 the circulation of the vine, having much the effect of a cancer. 



A great variation in the resistance to the disease is shown by many 

 varieties of European and American grapes. Of European grapes 

 the Muscat of Alexandria and the Mission of California were found 

 to be the most susceptible varieties. No species of Vitis vinifera 

 was found to be entirely immune. Some hybrids with American 

 varieties possess a high degree of resistance. Among these are the 

 Hupestris St. George and other similar varieties. The Lenoir pos- 

 sesses a high degree of resistance and is in many ways desirable as a 

 grafting stock. 



In Xew Mexico the varieties found most resistant were Feher 

 Szagos, Sweetwater, Seedless Sultana, Carignane, Grenache, Gros 

 Colman, Mataro, Black Malvoisie, Burger, and Lenoir. These vines 

 are more or less resistant on their own roots and are recommended 

 for planting in infected vineyards. A higher resistance to the disease 

 can be obtained by grafting these or other desirable varieties on such 

 stocks as the Rupestris St. George and the Lenoir, which are also 

 resistant to phylloxera. 



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