Minnesota Plant Diseases. 



325 



Sulphur dusting, spraying with ammoniacal copper carbon- 

 ate, have all given good results. The ground should not be 

 allowed to become infested with the resting spores (winter 

 spores), hence the diseased plant parts should be burned. 



Powdery mildew of gooseberry \Sphaerotheca mors-uvae 

 (Schwein.) B. & C.]. Gooseberries are not infrequently attacked 

 by this destructive disease. The leaves, fruits and shoots are 

 coated with a fine whitish mycelium. Summer and sac spores 

 are produced as is usual in the true powdery mildews, and the 

 sac capsule is in general like that of the rose mildew, though dif- 

 fering, of course, in minor details. 



There is another powdery mildew (Microsphaera grossu- 

 lariae) which is known to occur on the gooseberry though not 

 as commonly as that described above. It can be distinguished 

 by the many-times forked appendages on the sac-capsule and 

 by the large number of sacs in each capsule. 



"Spray with potassium sulphide as soon as buds break and 

 repeat about every ten days until end of June." (Conn. Ag. 

 Ex. Sta. Bull. 1421903.) 



Powdery mildew of hops(Sphaerotheca castagnei Lev.). This 

 is perhaps identical with the strawberry-leaf powdery mildew, 

 or a biologic form of this species. The mycelium of hop mil- 

 dew, like that of rose mildew, is superficial and forms a whif'sh 

 coat on the surface of leaves of hops. It also inhabits mem- 

 bers of the rose, composite and other families. The fungus 

 threads send sucker branches into the epidermal cells withdraw- 

 ing from the latter their nourishment. The sac-capsules are 

 similar also to those of rose mildew. Summer spores are also 

 similarly produced in chains. Where hops is raised in abund- 

 ance the mildew may cause very serious damage. 



Bordeaux or ammoniacal copper carbonate can be used as 

 a spray. 



Powdery mildew or blight of roses [Sphaerotheca pannosa 

 (Wallr.) Lev.]. See Diseases of Greenhouse and Ornamental 

 Plants. (See Figs. 203 and 204.) 



Powdery mildew of vetch and crowfoot [Erysiphe corn- 

 munis (Wallr.) Fr.~\. This is sometimes found on cultivated 

 plants of the pea family. See Diseases of Wild Plants. 



