A Study of Meadow-Crop Diseases in New York 97 



The copper sulfate might be diluted in water to determine the minimum 

 point of toxicity. 



No studies with copper-lime dust in the field have been made, but the 

 evidence in hand indicates rather clearly that sulfur dust at least may be 

 depended upon to control timothy rust in the field and that copper-lime 

 dust if not altogether inefficient, would certainly be less satisfactory than 

 the sulfur. 



Investigators have maintained that the only hope of combating the 

 trouble successfully lies in the development of disease-resistant plants. 

 Timothy varieties do vary in their susceptibility to the disease, as indicated 

 under varietal susceptibility, and, since no specialization of the fungus 

 seems to occur, the development of disease-resistant varieties of timothy 

 is not such an unpromising method as it seems to be in the breeding of 

 resistant varieties of wheat. 



Barker and Hayes (1924:370) show that resistance or susceptibility 

 seems to depend upon a single factor pair. " Resistance appears to be 

 dominant, and a close approximation to a 3:1 ratio was obtained in the 

 progeny of self-fertilized resistan plants." Proytchoff (1928) confirms the 

 conclusions of Barker and Hayes in general, but he thinks that he has some 

 evidence of modifying factors influencing the degree of resistance. The 

 nature and the number of these factors were not determined. 



CERCOSPORA LEAF SPOT OF GRASSES 



Stiscepts 



According to the writer's collections, Cercospora leaf spot attacks 

 timothy, orchard grass, red top, blue-grass, and Alopecurus geniculatus 

 in New York. In published records the following additional species of 

 grasses are recorded as suscepts: Bromus unioloides, Harden m jubatum 

 (Spegazzini, 1911:436), Bromus marginatus, Bromus sitchensis, Horde um 

 nodosum, Elymus glaucus, Elymus robustus (Johnson and Hungerford, 

 1917: 69), Alopecurus fulvus, Oryza clandestina, Milium effusum, Poa 

 nemoralis, Glyceria fluitans, Glycerin plicata (Schroeter, 1908:498), An- 

 thoxanthum odoratum, Arrhenatherum elatius, Avena elatior, Avena saliva, 

 Brachypodium sp., Cynosurus cristatus, Glyceria aquatilis, Poa compressa, 

 Poa trivialis, Secale cereale (Lindau, 1907:794), and Avena bulbosa (Tracy 

 and Earle, 1895 b:115). 



The disease 



The malady, for which the name Cercospora leaf spot is proposed, prob- 

 ably is the most important disease of timothy in the State at the present 

 time. It is serious also on orchard grass. It seems to have been recorded 

 first in America by Trcleasc (1887). The writings indicate that it is very 

 widely distributed, at least in America and Europe. 



