188 SEVENTEENTH REPORT. 



AN EPIDEMIC OF CROXARTIUM OOMrTONIAE AT THE 

 ROSCOMMON STATE NURSERIES. 



BY C. H. KAUFFMAN AND E. B. MAINS. 



During the first week of August, 1914, information came to hand 

 that the pine plantations at Roscommon were seriously affected by 

 a rust. At the request of the Public Domain Commission, Mr. E. 

 B. Mains was sent to investigate conditions there. It was found 

 that 12 to 15 acres devoted to Western Yellow Pine (P. po)iderosa) 

 and Lodgepole Pine (P. contorta) already five year old seedlings, 

 were infested with one of the blister rusts : Cronartium Comptoniae. 

 Almost every seedling was attacked, some dead, the majority in the 

 last stages of the disease. The stems of the seedlings were strongly 

 hypertrophied so that fusiform SAvellings resulted. Breaking 

 through the bark of the swollen parts were large clusters of the 

 aecidia. This stage is Periderniiuni Comptoniae. Large plantations 

 of Scotch Pine bordered the affected areas, but were not affected. 

 In the nursery the rust had also destroyed or was destroying the 

 younger seedlings. Here it had attacked also some Austrian Pine 

 seedlings but these had been pulled up by that time. The disease 

 was first noticed in 1911 in the nursery. Diseased s^eedlings and 

 those which had died were occasionally pulled up by the men in 

 charge, but as the serious nature of the disease was not realised no 

 especial attempt was made to eradicate it. 



As these rusts are heteroecious, before any certainty concerning 

 the species could be arrived at. it was necessary to determine what 

 the teleutos])ore host might be. This was comparatively ea.sy, since 

 merely a glanc/3 at the leaves of the Sweet Fern (Mijrica aspleni- 

 folia) which grew abundantly throughout the plantations and over 

 all the surrounding country, showed them to be badly infected with 

 a rust. Examinati(ui showed the leaves to be covered in places by 

 the pustules of the uredospore and teleutospore stage of Cronartium 

 Comptoniae. The Sweet Fern in both the nursery and the two 

 fields of Yellow and Lodgepole Pine was densely rusted. The pre- 

 vailing winds here are from the west. On examination of the Sweet 

 Fern In^yond the edge of the ])lantations, Mr. Mains found the rust 

 al)sent from the Sweet Fern on the west side and the north-west 

 side; but on the east where the wind had carried the spores from 



