3o2 THE RUSTS OF NOVA SCOTIA. FKASEK. 



probably tend to reduce the fungus by devouring the spores, 

 but they may aid in their distribution by spreading them as 

 they crawl about. 



Economic Aspects of the Rusts. 



The rusts are true parasites and unable to live except in 

 the tissues of their hosts. They attack many valuable trees 

 and shrubs as well as field and garden crops, and, as they live 

 at the expense of their hosts, often cause serious damage. They 

 cannot be combatted with much success by spraying with the 

 Bordeaux or other mixtures. Usually a knowledge of their 

 life history will alone suggest some method of holding them in 

 check. 



Rusts of the Conifers : Many rusts of the genus Coleo- 

 sporium and Cronartium have their aecial stages on some 

 species of pine, but no rusts were found on the pine in Nova 

 Scotia and none are likely to occur, unless the European 

 currant rust (Cronartium rubicola) should be introduced. The 

 aecial stage is found on the white pine (Pinus strobus) and is 

 said to be very destructive in Europe. The uredinial and 

 telial stages on currant bushes does not seem to be of much 

 importance. An outbreak occurred at Geneva, 1ST. Y., in 1906, 

 and in 1909 pine seedlings which were imported from 

 Germany and were distributed through the north eastern 

 United States and Canada were found to be diseased. The 

 only way to control the fungus would seem to be to destroy 

 the wild species of Ribes in the neighbourhood of the pine 

 forest areas. 



The leaves of the balsam fir (Abies balsamea) are attacked 

 by the aecial stage of the blueberry rust (Calyptospora column~ 

 am) by Peridermium balsameum and by a Caeoma. The 

 spores are formed on the under side of the leaves which turn 

 yellowish. Peridermium, elatinum, the aecial stage of 

 Melampsorella elatina, forms the rather conspicuous witches' 

 brooms on the same host. These may be removed in the spring 



