462 



DISEASES OF ECONOMIC PLANTS 



in 1896 in Massachusetts. It was rapidly spread through- 

 out this country by diseased stock, and is now known 

 in nearly all localities where the chrysanthemum is culti- 

 vated. The loss occasioned by the diminution in vigor 

 of the plant and consequent imperfection of blooms is 

 large. 



The sori, 2-3 mm. in di- 

 ameter, which are diagnostic, 

 first appear as small blisters 

 covered by the epidermis. 

 The rupture of this covering 

 discloses a dark brown mass 

 of spores. The sori are usu- 

 ally very numerous upon the 

 lower leaf surface, less abun- 

 dant above, and the spores as 

 liberated form dusty coatings 

 upon the leaves. Badly af- 

 fected leaves curl, shrivel, and 

 die. The plants are dwarfed 

 and fail to produce flowers of 

 value. 



All new stock introduced to the houses should be care- 

 fully inspected and all diseased stock destroyed by fire. 

 New stock should be isolated and watched for a month or 

 more to be sure that no rust develops. If disease appears, 

 all affected leaves should be picked and burned with pre- 

 cautions to avoid scattering the spores. If the rust con- 

 tinues to appear, all aboveground parts must be destroyed 

 by fire at the end of the season, and plants for the next year 

 raised in uncontaminated soil and house. 



Fig. 199. — Chrysanthemum leaf sliow- 

 ing rust sori. Origina 



