WHITE-PTXE BLTSTl^.E RUST. 73 



CONTROL OF THE WHITE-PINE BLISTER RUST. 

 Significant Factors Which Determine Control. 



* FACTORS IN THE FUNGUS. 



The significant features in the life history of Cronariium rihicola 

 are as follows: The pycnospores are apparently functionless ; the 

 aeciospores are not known to infect pines, but they do infect Ribes 

 readily; the urediniospores are not known to infect pines, but they 

 do infect Eibes; the sporidia produced by the teliospores are not 

 laiown to infect Ribes, but they do infect pines. 



The spores are all distributed by the wind much more than by any 

 other agency. The seciospores are carried and are capable of infect- 

 ing Ribes leaves miles away from their source. The urediniospores 

 are distributed a number of hundred yards, but appear to lose their 

 viability soon, so that infection by them is rather limited in extent. 

 The sporidia produced by the teliospores appear to be distributed 

 to a distance of a few hundred yards, but they are so frail that they 

 soon lose viability. Infection by them is limited to 100 to 600 3^ards 

 as a general thing, and more commonly the former than the latter 

 distance. 



The fimgus lives over winter most commonly by means of the 

 mycelium, presumably in the needles and certainly in the bark of 

 infected white pines. It occasionally overwinters by means of the 

 asciospores in cankers of pine bark or by the urediniospores on Ribes 

 leaves. The seciospores produced by the overwintered mycelium 

 in the pine bark are the principal source of infection of the Ribes 

 leaves each spring. The seciospores carry the disease far and wide 

 for miles to the new Ribes leaves. The urediniospores intensify 

 the disease in the vicinity where it is started by the seciospores. 

 The sporidia carry the disease back to those pines which are rela- 

 tively near infected Ribes bushes. 



High humidity of the air is necessar}^ for any of the spore forms to 

 germinate and to produce infection. 



FACTORS IN THE ENVIRONMENT. 



CLIMATIC FACTORS. 



Climate may be reduced to the three most potent factors — mois- 

 ture, sunshine, and wind. Cronartium rihicola is absolutely de- 

 pendent upon abundant moisture for its development. Drought, 

 especially if prolonged, apparently may hinder the development of 

 the secia (49, 135). Lack of moisture prevents germination of all 

 the different forms of spores. It prevents or very greatly reduces 

 the extent of infection on Ribes plants by reciospores. It prevents 

 the production of new generations of urediniospores, ^^ and conse- 

 quently prevents the abundant formation of uredinia as well as 



i^ PemiinRton, L. 11. Op. cit. 



