A Study of Meadow-Crop Diseases in New York 119 



and not easily included in this table are: (1) the results of laboratory 

 tests of fungicides vary with the dosage of material on the slide, especially 

 if the chemical in question is diluted to or near to the point of minimum 

 toxicity; (2) sulfur dust is no more effective at higher temperatures than 

 at lower ones, which indicates that it does not act through volatilization 

 or, if it does, it volatilizes with sufficient rapidity at low temperatures 

 to be effective in the cases recorded; (3) hydrated lime apparently has 

 no fungicidal effect on any of the fungi tested except Puccinia phlei- 

 pratensis, but it appears to inhibit markedly the germination of the spores 

 of this fungus, being as toxic as the copper sulfate in copper-lime dust; 

 (4) talc has no visible effect upon spores of Helminthosporium vagans, 

 H. triseptatum, or Macrosporium sarcinaeforme; (5) staling products 

 accumulate in moist chambers used for germinating spores, so that the 

 dishes should be washed carefully after each test. 



Most of the essential facts about each disease are summarized in table 35 

 to avoid a lengthy summary and to facilitate reference. 



Some additional facts regarding certain of the pathogenes that do not 

 appear in table 35 may be stated briefly: (1) spore production in culture, 

 induced in Helminthosporium vagans and Pseudoplea trifolii, by exposure 

 to out-of-door conditions is due to the effect of light; (2) culture mutations 

 in Helminthosporium vagans are stable as a rule after passage through the 

 suscept, although work with fungous mutations reported prior to the time 

 this work was initiated had not taken this factor into account; (3) spores 

 of Macrosporium sarcinaeforme germinate equally well at all temperatures 

 from 3° to 35° C; (4) no cicatrice is laid down in red-clover leaves to 

 halt the invasion of this pathogene; (5) powdery mildew has been shown 

 to be very deleterious to red clover, contrary to most opinions; (6) by 

 removing the water from the leaves, the fungus causes them to be deficient 

 in photosynthetic ability, which results in stunting, the most significant 

 symptom of powdery mildew; (7) clover extract stimulates the germination 

 of the conidia of Erysiphe polygoni and Dothidella trifolii; (8) cool nights 

 and warm days appear to be conducive to the spread of E. polygoni; 

 (9) the pathogene causing the Cercospora leaf spot of clovers and alfalfa 

 is Cercospora zebrina Pass.; (10) the writer agrees with Petrak that Pseu- 

 doplea trifolii is the cause of similar diseases of the clovers and alfalfa, 

 and that Stagonospora meliloti also causes diseases that are similar to each 

 other on the same suscepts; (11) girdle of alfalfa, sweet, and red clovers, 

 and bacterial leaf spot of clovers, have been found in New York; 

 (12) Cercospora graminis is the name that should be applied to the fungus 

 commonly called Scolecotrichum graminis; (13) Helminthosporium vagans 

 attacks orchard grass as well as blue-grass (producing mutations which 

 pass unchanged through the suscept) , consists of physiologic forms, has been 

 induced to sporulate in culture by exposure to light, and overwinters as 

 mycelium in living leaves. 



