DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 49 1 



the bark and into the bark crevices, causing the bark to crack and 

 peel. Later a new bark forms under the old. The new bark is not 

 sufficiently resistant to the attacks of species of Diplodia and Nectria, 

 so that these fungi may enter and complete the work of destruction. 

 Corticium Hlaco-fuscum gtows more rapidly in damp, shady places, 

 and it usually refuses to grow in sunny places, hence opening up the 

 growth is beneficial. 



Cherry (Prunus spp.) 



Leaf-curl {Exoascus cerasi (Fckl.), Sadeb.). — This fungus produces 

 witches' brooms out of the twigs of the cherry, and when the leaves on 

 affected twigs are parasitized, they become somewhat reddish and 

 curled. The asci develop on the leaves and measure according to 

 Sadebeck, 35 to $ofi by 7 to lo^, or in specimens studied by Atkinson, 

 25 to 33/i by 6 to 9/i. The asci are naked and arranged in rows over the 

 leaf surface. Spraying, if done at all should be done when the buds 

 begin to develop in the Spring, and again when the asci are mature 

 and ready to discharge their spores. 



Powdery Mildew (Podospkara oxyacanthcR (DC), deB'y). — This 

 disease, although found on a number of other rosaceous plants, 

 such as plums and hawthorns and the like, is especially destructive to 

 apples and cherries. The leaves become mildewed with large spots 

 of white mycelium from which arise the perithecia, which are 65 to 90/i 

 in diameter surrounded by the dichotomously branched hyphal append- 

 ages four to thirty in number, which are usually five times as long as 

 the diameter of the perithecium. A single ascus usually contains 8 

 ascospores. It is recommended to spray with lime sulphur (1-40) 

 or dust with powdered sulphur in combating this disease. 



Chestnut {Castanea dentata (Marsh.) Borkh.) 



Blight {Endothia parasitica (Murrill), Anderson).' — When the chest- 

 nut blight fungus was first described by Murrill he called it Diaporlhe 

 parasitica, but by the studies of Anderson and others it has been trans- 

 ferred to the genus Endothia, where it seems rightly to belong.^ On 

 account of its virulency and its rapid spread through the chestnut 



1 Shear, C. L., Stevens, Neil E., and Tiller, R. J. : Endothia parasitica 

 and Related Species. Bull. 380, U. S. Dept. Agric. 



