400 



MANUAL OF FRUIT DISEASES 



developed. In their full maturity they appear as black specks. 

 The tissue about them is yellowish. These bodies are not 

 found on all leaves nor on all leaflets of a given leaf. Two or 

 three weeks after the appearance of these structures evidence 

 of rust is seen on the lower surface of the leaves. When mature, 

 these bodies (sori) break open and expose an orange-colored 



mass of spores ; 

 whence the name 

 orange-rust. Ordi- 

 narily these sori 

 with their spore- 

 masses practically 

 cover the lower sur- 

 face of the leaf. 

 Affected leaves are 



"*_! tf^vaB* dwarfed and rolled, 



ij*fc^ Vyf ^^3JHC" somewhat exposing 



the orange-colored 

 lower surf aces. Rust 

 is rarely found on 

 the canes. This 

 stage gradually dis- 

 appears during the 

 latter part of June, 

 until by July it is difficult to find in northern United States. 

 Farther south, on a parallel with Maryland, orange-rust may 

 be seen in late summer and sometimes in the fall. Affected 

 plants are noticeably stunted (Fig. 117) but are not killed. 

 Plants once affected are almost certain to be diseased again 

 the following year. Some rusted plants show a reduced 

 number of prickles. 

 Cause. 



The bramble fungus, Gymnoconia interstitialis, is the cause 

 of this disease. Its mycelium lives from year to year in the 



FIG. 117. Orange-rust ; healthy plant on right, 

 diseased on left. 



