296 THE PARASITIC DISEASES OF PLANTS. 



plant in such a way as to render it best able to resist the disease. 

 This involves the matter of cultivation, fertilizing, controlling weeds 

 that serve as hosts of the parasite, etc., and demands a knowledge 

 of the methods and seasons for the spore distribution of the fungi, 

 and each disease has to be studied as a separate problem. 3. By 

 the use of fungicides. These are properly selected chemicals that 

 act as powerful germicides upon the fungi, but do not injure the host- 

 plant. They are mostly applied by spraying, and the spray reaches 

 the surface of the plants only, being, therefore, of little or no value 

 after the mycelium has actually entered the plant tissue. Hence 

 to be useful they must be applied at just the right time, and each 

 disease must be carefully studied as to its time of sporing in order 

 that spraying may be a success. A majority of the successful 

 fungicides contain copper that seems to be especially efficient upon 

 this class of fungi. 4. With some of these diseases a rotation of 

 crops is efficient, since a fungus that attacks one host may be without 

 influence upon another species of plant. 5. Clean seed selection; i.e., 

 selection of seed free from disease. 



To describe the various fungoid diseases is impossible in this 

 work. A list of the more important ones is given below, classified 

 according to their host plant, with the popular name and the name 

 of the fungoid parasite. 



Alfalfa. Leaf spot, Pseudopeziza Medicaginis (Lib.) Sacc. 



Apple. Bitter rot, Glomerella rufomaculans (Berk.) Sp. and 

 von Schr. Black rot, Sphceropsis malorum Pk. Canker, Nectria 

 ditissima Tul. Leaf spots, Phyllosticta. Powdery mildew, Podo- 

 sph&ra leucotricha (Ell. and Ev.) Salm. Rust, Gymnosporangium 

 macropus Lk. Scab, Venturia inaqualis (Cke.) Aderh. Sooty 

 blotch, Phyllachora pomigena (Schw.) Sacc. 



Asparagus. Anthracnose. Fusarium, Rust, Puccinia asparagi 

 DC. Rust, Cladosporium herbarium Link. 



Beans. Anthracnose, Colletotrichum lindemuthianum (Sacc, and 

 Magn.) Bri. and Cav. Downy mildew, Phytophihora Phaseoli 

 Thax. Leaf blotch, Isariopsis griseola Sacc. Rust, Uromyces 

 appendiculatus (Pers.) Lk. 



Beet, Leaf blight, Cercospora beticola Sacc, 



