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CONTROLLING THE HOLLYHOCK RUST 1 



Now that the hollyhock season is over it is time to begin opera- 

 tions designed to control the rust disease that is so often prev- 

 alent in our flower gardens. This parasite is one of the simplest 

 of the rust fungi. It is now known that the brown spores found in 

 tbe rusty spots on the leaves and stems germinate just as soon as 

 they are mature if provided with moisture. During germination 

 the spots turn color from brown to ash gray. As many thousands 

 of sporidia, each capable of initiating a new infection, are developed 

 on the spots, one understands how it is that the leaves become so 

 heavily infected and how difficult it is to prevent the spread of the 

 infection once the rust has become established. 



Since the rust appears early in the spring with the first leaves, 

 one might suspect that the parasite overwinters in the roots or 

 crown. A noted Scandinavian pathologist always claimed that 

 the hollyhock rust is perennial in its host, appearing with the new 

 growth in the spring. This claim has been thoroughly disproved, 

 however. Every spot on a leaf is the result of a new and separate 

 infection. Very late in the season the new crown leaves may be- 

 come infected. This new infection may carry the fungus through 

 the winter, as the plants are dormant. 



The brown spores may also remain viable all winter and so in- 

 fect the first spring leaves anew. In either case it shows how im- 

 portant it is to destroy all of the old infected plants, stems as well as 

 leaves, after the blooming period. Otherwise, the infected parts 

 bearing spores collect on the ground over the crowns and thus 

 they either bring infection to the tips of the late fall crown leaves, so 

 that the fungus goes into a dormant condition along with these leaf 

 primordia, or the spores, living over winter, cause the early leaves 

 to become infected. 



It is often stated with some confidence by authors that tbe 

 hollyhock rust can be controlled by dusting tbe plants with a fine 

 grade of sulphur. Any one who has tried this after the infected 

 plants have reached some height knows that such measures are not 

 always successful. It requires only about twenty-four hours for 

 the spores to germinate and penetrate the host tissues, and some 

 six to ten days for new pustules to mature. Xew leaves are con- 



1 Puccinia malvacearum. 



