EXPERIMENT STATION BULLETINS. 



375 



DISEASES OF THE CHERRY. 



POWDERY MILDEW. 



(Podosphaera oxyacanthae (D. C.) De By.) 



Fig 25. — Powdery mildew of the cherry, etc. A, a winter spore case (perithecium) magni- 

 fied, showing the appendages with peculiarly branched tips; b, the one large spore sac 

 (ascus), containing eight spores, which is contained in the spore case, a; c, the summer 

 spore form of the fungus showing [the formation of spores (conidia), by the dividing of a 

 spore stalk (conidiaphore) ; d, a spore germinating in water. (Magnified, original.) 



The powdery mildew is a superficial fungus, that is, it spreads over the surface 

 of the host plant merely sending short sucker-like growths (haustoria) into the 

 epidermal cells. These serve alike the purposes of hold-fasts and feeding organs 

 for the parasite. This disease appears on the foliage producing a white, moldy 

 appearance due to the numerous mycelial threads which form a delicate felt- 

 like layer. From these threads arise minute, erect stalks which divide into a 

 number of cells each of which becomes an egg-shaped spore. The great number 

 of these spores forming on the surface of the leaf gives a powdrery appearance 

 suggestive of the common name. These are the summer spores. They germi- 

 nate as soon as they fall into a drop of moisture and if in contact with a young 

 cherry leaf set up the disease. Later in the season dark brown specks appear 

 among the matted threads of mycelium, each armed with a number of thread- 

 like appendages furnished with peculiarly branched ends. These dark bodies 

 are the resting spore cases which remain dormant through the winter and give 

 off several spores in the spring to start the disease anew. 



The powdery mildew, while not often serious on large trees, may cause much 

 damage to the leaves and tender shoots of seedling cherries in the nursery. The 

 same disease is common also on the foliage of the plum, young apples and haw- 

 thorn. 



Treatment. — Trees which are treated for shot-hole and brown rot with Bordeaux 

 mixture will need no further treatment for this disease. For seedl'ing trees the 

 sulphide of potassium solution or the ammonium copper carbonate mixture may 

 be used. 



BUST. 



(Puccinia pruni-spinosae Pers.) (See on Peach.) 



SCAB. 



(Cladosporium carpophilum Thum.) (See Peach Scab.) 



The cherry is subject to a number of diseases common to the plum. Among 

 these the following are described under the head, — 

 Black Knot { Plotcrightia morbosa (Schw.) Sacc). 



Brown Rot, Fruit Mold (Sclerotinia fructigena (Kze. & Schm.) Norton). 

 Shot-hole Fungus, Leaf Spot {Cylindrosporium Padi Karst). 



