THE CHERRIES OF NEW YORK 89 



Black-knot looks more like the work of an insect than a fungus and was 

 long supposed to be such even by those who were studying the trouble. 

 The knots begin to form early in the summer and are of characteristic 

 color and texture — dark green, soft and velvety, but in the fall, as the 

 fungus ripens, the color changes to coal-black and the knots become hard 

 and more or less brittle. The excrescences usually form on one side of 

 a twig or branch so that death seldom follows quickly. The disease attacks 

 both wild and cultivated plants in every part of this continent where 

 cherries are grown but is epidemic only in the East, the cherry regions 

 of the West being practically free from the disease. Up to the present 

 time the fungus has not been found elsewhere than in America. Happily, 

 black-knot may be controlled by cutting out the diseased wood. To 

 completely eradicate the fungus, if it is especially virulent, however, the 

 orchard must be gone over several times during a season. In New York 

 the removal of black-knot is ordered by law, the results showing that 

 when the law is obeyed, especially if there be hearty co-operation among 

 growers, eradication is usually possible. Sweet Cherries are much less 

 attacked by black-knot than the Sour sorts but the differences in immunity 

 between varieties in either of the two species are not very marked — at 

 least such is the case on the grounds of this Station where the disease 

 is always present and is often very prevalent. 



Exoascus cerasi Fuckel ' is the cause of a very striking deformity of 

 the cherry in Eiu"ope, both Primus avium and Primus cerasus being 

 attacked. The disease has been reported in America but has not yet 

 become virulent. The fungus attacks the branches, causing a clustering 

 of the twigs in the form of a broom, giving it the name witches' broom. 

 The leaves on the diseased twigs usually take on a crinkled shape and a 

 reddish color. The malady may be readily prevented by the destruction 

 of affected branches. 



In common with other species of Prunus the foliage of cherries is 

 attacked by several fungi which produce diseased spots on the leaves, the 

 dead areas usually dropping out leaving holes as if punctiired by shot. 

 Thus we have " shot-hole fungus," " leaf-spot " and " leaf -blight " as 

 effects of these diseases. Three fungi are in the main responsible for these 

 leaf troubles; these are Cylindrosporium padi Karsten,^ MycosphcBrella 



• Duggar, B. M. Fungous Diseases of Plants 185, fig. 68. 1909. 



'Higgins, B. B. Contributions to the Life History and Physiology of CyHndrosporium on Stone 

 Fruits, Am. Jour. Bot. 1:145-173. 1914. 



