430 Diseases of Economic Plants 



the entire leaf is more often involved than in the above 

 diseases, and definite spots are more rare. Dark acervuli are 

 present. 



Gray-mold {Botnjtis sp.). — This occurs upon leaves and 

 flowers much as upon lettuce. 



Bordeaux mixture is useful with all of these primrose 

 diseases. 



PRIVET 



Anthracnose ^"^ {Glomerella cingulata, Gloeosporium). — 

 Twig blight superficially resembling that of the pear is a 

 character of this disease in its later stages, terminal parts of 

 the twigs 2-5 cm. long being affected. The line of separation 

 between diseased and healthy tissue is sharp through shrink- 

 ing and depression of the diseased part. In early stages de- 

 pressed, oblong, diseased spots, at first very minute, are seen 

 upon the bark. These spots enlarge, eventually girdle the 

 twig, and cause the death of the distal part. Minute black 

 elevated acervuli, visible to the naked eye, are scattered over 

 the surface of the original disease spots. 



Affected branches should be cut well below the diseased 

 portion and burned. A spring spraying, before the buds 

 swell, with any good dormant spray will still further reduce 

 infection. 



ROSE ^^^ 



Black-spot ^^^ (Diplocarpon rosce Wolf, Actinonema) . — 

 Both in and out of doors, this is a widely known and destruc- 

 tive rose disease. It was first described in 1824, and is now 

 widely distributed throughout Europe and the United States. 

 It consists of irregular circular or oval indefinitely bordered, 

 black spots upon the upper surface of leaves that are mature 

 or nearly so. The larger spots are a centimeter or more in 

 diameter, and they frequently coalesce so as nearly to cover 

 whole leaflets. 



With age the spots turn gray at the centers, at which part 



