96 Diseases of Economic Plants 



purely upon the surface its development may be prevented 

 by spraying. Selby reduced the injury from 16 per cent to 

 1 per cent by three applications of Bordeaux mixture. 



Rust {Transchelia punctata (Pers.) Arth.). — A true rust 

 exists upon the peach, plum, and cherry and near kin. While 

 more common upon the plum, it very frequently does damage 

 to the peach, in some cases being so serious as to cause almost 

 complete defoliation. The alternate stage is not uncommon 

 upon the hepatica in the spring. 



This malady will be recognized by the presence of small, 

 round, dusty sori on the lower surface of the leaves and on 

 the young shoots, while in the inunediate region of these 

 spore-bearing pustules, the leaf, seen from above, often 

 presents a reddish or reddish yellow color. 



Stem-blight (Phoma yersicce Sacc). — A fungus on the 

 bark which fructifies in minute pustules sometimes causes 

 twigs to die. The disease may be recognized by the dead 

 bark thickly studded with small pycnidia. Burning the 

 diseased branches will prevent spread of the pest. 



Frosty-mildew (Cercosporella persica Sacc). — In damp, 

 shaded localities, especially on trees of dense foliage, a disease 

 occurs in the form of pale-yellowish leaf spots. These show, 

 on the underside, a delicate frostlike appearance, due to the 

 growth of white spore-bearing hyphse. It is not usually 

 serious, though widespread, and sprays recommended else- 

 where suffice to hold frosty-mildew in check also. 



Cercospora shot-hole {Cercospora circumscissa Sacc). — 

 This is very widespread, producing spots, or, when the 

 diseased tissue falls out, oval holes, in the leaves. It also 

 infects small branches. The chief injury lies in destruction 

 of leaf tissue and of valuable shoots. Dormant spraying 

 recommended for the curl is useful here. Phyllosticta shot- 

 hole {Phyllo.siida circumscissa Cke.). — Similar in appearance 

 and effect to Cercospora shot-hole, it responds to like treat- 

 ment. Armillaria and Clitocybe root-rots, see apple; Silver- 

 leaf, see plum. 



