366 Minnesota Plant Diseases. 



several years is necessary to hold it down to a minimum of dam- 

 age. Spraying with bordeaux has been found very beneficial. 

 Spraying should commence early and continue at intervals of 

 about two weeks until a few weeks before the ripening of the 

 fruit. In these later sprayings, ammoniacal copper carbonate 

 should be substituted for the bordeaux. 



Powdery mildew of vines [Uncinula necator (Schw.} Burr.]. 

 This is one of the most destructive of the powdery mildews or 

 blights. It attacks grape vines and causes much damage, not 

 only to the leaves but also directly to the fruit. The summer 

 spores are formed in the usual manner for powdery mildews and 

 appear in great numbers spreading the disease very rapidly. The 

 spread is particularly rapid in moist weather. The mycelium 

 first appears in whitish areas, under which the cells of the leaf 

 are killed, leaving brown spots. The leaves usually wither. The 

 grapes dry up in the attacked region and often become split open 

 and subsequently wither or decay. The summer spores are 

 formed throughout the summer; and in the fall the sac spore 

 capsules appear as dark-brown bodies o<f minute size. The cap- 

 sule is provided with a crown of numerous thread-like append- 

 ages, the tip of each of which is bent back in the form of a stout 

 terminal hook. When broken open each capsule is found to con- 

 tain four to ten sacs, each of which contains four to eight spores. 

 The disease winters over in the capsular stage and infection is 

 accomplished in the spring from the sac spores, which alight on 

 the leaves. Here they send out a small tube with a flattened 

 disc, which serves to attach the parasitic plant to the leaf. A 

 short sucker branch is then sent out into a cell of the host and 

 the growth of the mycelium proceeds. From this mycelium the 

 summer spores arise. 



"Treat as for downy mildew with perhaps a late spraying in 

 the fall after gathering the berries, to destroy the winter spores. 

 Potassium sulphide is also used effectively against this fungus." 

 (Conn. Ag. Ex. Sta. Bull. No. 142 1903.) 



"The sprayings with bordeaux mixture, that are generally 

 applied for other diseases, will do much to hold it in check, during- 

 the early part of the season ; but later on, *as the fruit approaches 

 maturity, the weak copper ,sulphate or the ammoniacal carbonate 

 of copper will be preferable. The application of flowers of sul- 



