EXPERIMENT STATION BULLETINS. 369 



surface of the leaves which are induced to fall off prematurely. This disease is 

 troublesome in the southernmost states. 



PEACH MILDFAV. 



( Sphaerotheca pannosa Lev. & Podosphaera oxyacanthae (D. C.) D. By.) 



Mildew attacks leaves and twigs and later the fruit also, covering the former 

 with a whitish coating and on the latter producing spots of a light color, harden- 

 ing of the flesh and an abnormal development of hairs or fuzz. Only those 

 varieties which have serrate margined leaves and do not possess glands on the 

 leaves seem to be affected. It is readily controlled by copper sulphate solution and 

 Bordeaux mixture. 



BROWN OR PUSTULAR SPOT. 



(Helminthosporium carpohilum Lev.) 



This disease was first noticed in Michigan in 1893 as being most common on 

 the Wager variety. Affected fruit shows small, rusty spots which gradually 

 increase in size after the fruit begins to ripen. The disease is confined to the 

 surface of the fruit hence is readily controlled by spraying with fungicides. 



COXSTRICTIOX DISEASE OF STEJI AND BRANCH. 



(Phoma persicae Sacc.) 



A disease which causes a groove-like constriction of the stems and branches 

 of peach trees, due to a fungous parasite has been described as occurring on 

 nursery stock and on young shoots of older trees in Ohio. The portions of the 

 stem or branch above the constriction die back. Cutting off the affected parts 

 below the constriction is recommended, the removed portions to be burned. 



SHOT HOLE FUNGUS. 



(Cylindrosporium padi Karst) (See Plum). 



LEAF SPOT FUNGI. 



Several fungi of a more or less parasitic nature have been noticed as occurring 

 on peach leaves, being associated with spotting of the foliage. Among these are 

 Macrosporium commune Rabh.. recorded as frequent in Ohio, and Cercosporella 

 persica Sacc. The latter fungus produces a frosty growth on the under surface 

 of the spots. It is more common in the south than here. Neither of these fungi 

 is to be regarded as serious in its effects. 



Cercospora circumscissa Saac, also causes spotting of the leaves of the leaves 

 of peach, cherry, almond and apricot, the pieces of dead tissue falling out later 

 thus giving rise to a shot-hole effect. 



PLUM DISEASES. 



BLACK KNOT. 



(Plowrightia mqrbosa (Schw.) Sacc.) 



Black knot of the plum and cherry is one of those destructive fungous diseases 

 the effects of which are quite liable to be mistaken for the attacks of some insect 

 parasite. In fact, for a long time it was believed even by scientists that the 

 peculiar black, knotty growths which often appear on these trees were due to 

 this cause. It is definitely known, however, that these knots are the direct result 

 of the presence of the mycelium of a fungous parasite in the tissue of the branches 

 and that insect larvie when found are merely feeding on the swollen tissues. 

 The first evidence of the presence of this disease is the formation of irregular, 

 knotty swellings on the young growth, the knots often extending along the 

 branch more on one side than on the other, in such cases the branches being 

 frequently much curved or distorted. At first these knots possess a dark olive 



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