Minnesota Plant Diseases. 365 



The branch should be cut six inches below the canker and 

 care should be taken to keep the knife clean, since it is an easy 

 matter to transfer the bacteria on the knife blade to healthy 

 trees. The blade should therefore be dipped in a corrosive sub- 

 Hmate solution. All diseased twigs should be promptly burned. 

 Since an abundance of moisture in the plant favors the develop- 

 ment of the bacteria, an avoidance of a too succulent condition 

 has been recommended, e. g., draining the moisture from around 

 the base of the tree. This procedure has aided in keeping the 

 disease in check. 



Downy mildew of seedlings (Phytophthora omnivora DeBy.). 

 See Diseases of Greenhouse and Ornamental Plants. 



Vineyards. 



Black rot of the vine \Guignardia hidwellii (Ell.) Viola et 

 Rav.']. This fungus has often proved a very destructive disease 

 and vine growers in the United States have suffered great losses 

 from it. The extent of damage in Minnesota is as yet unknown, 

 though the fungus is probably not uncommon. It has caused 

 considerable trouble in Iowa. The first indication is the produc- 

 tion of small reddish or brownish spots on the leaves. On these 

 spots arise minute, black, capsular fruiting-bodies. These cap- 

 sules do not contain sac-spores, but produce one kind of summer- 

 spore. These spores are formed on threads in the capsule and 

 escape in a sticky mass from the apical opening. They are 

 washed apart by the rain and distributed to other parts of the 

 plant. The berries are also attacked and brownish spots appear 

 on them. Capsular summer spores are formed here similar to 

 those on the leaves and in addition to these two other spore-forms 

 may appear. The berry shrivels and dries up and becomes black, 

 but still clings to the vine. Late in the fall the sac-spore cap- 

 sules appear on the shriveled grapes. They are small black 

 bodies with an opening, through which the sac spores escape in 

 the following spring. These sac spores probably recommence 

 the infection. All diseased portions should be promptly removed 

 and burned. All infected grapes should be destroyed and in no 

 case should the shriveled grapes be left on the vine until spring. 

 The disease needs prompt and persistent attention and a fight of 



