PLUM DISEASES 379 



winter-over, are viable in the spring, and can cause new infec- 

 tions after several months' rest. 



After the uredospores have been developed they are replaced 

 in the sori by other spores, known as teliospores. These follow 

 closely the development of uredospores ; they are said to appear 

 in five to twenty days after the uredospores. The teliospores 

 germinate in the spring, producing small, light sporidia which do 

 not infect the stone-fruits, but must go to species of Anem- 

 one, Thalictrum and Hepatica, all common wild flowers. 

 On any of these flowers germination and infection occur. The 

 mycelium developed in these hosts lives over until spring, when 

 fruiting sori-bearing seciospores are produced. Just preceding 

 these bodies sterile structures known as pycnia are developed 

 on the upper surface of the leaves as black dots. The mycelium 

 in the leaves may live over in these wild flowering plants for 

 several years in succession, so that the stone-fruits are not 

 absolutely necessary to the perpetuation of the fungus on these 

 wild flowers. In this connection, however, it should be noted 

 that the wild flowers already enumerated are necessary to the 

 perpetuation of the fungus on stone-fruits. The seciospores 

 developed on Anemone and others are wind-borne to the plum, 

 where infection occurs on the leaves. Within three weeks after 

 inoculation uredospores are mature and ready for summer dis- 

 semination of the fungus. Plum-trees are not generally attacked 

 until sometime after the month of June, except in Australia, 

 where infection occurs in February and March. 



Control. 



In those sections where plum-rust is troublesome it is probable 

 that spraying will reduce the injury. The treatment as advised 

 for peach leaf-curl, that is, spraying before the buds open with 

 some standard fungicide, is recommended. In southern Cali- 

 fornia it appears that early fall pruning performed to such an 

 extent that fall growth is stimulated is not advisable. The 

 difficulty involved lies in the fact that such foliage remains alive 



