178 FUNGOUS DISEASES OF PLANTS 



Losses. The losses from leaf curl may not be so readily esti- 

 mated as with many other fungous diseases, for the injury to the 

 fruit is usually indirect, through the loss of leaves and the gener- 

 ally impaired vitality of the tree. Before the adoption of any 

 rational preventive measures the losses in the United States were 

 estimated at about three million dollars. In general, heavy losses 

 in the South, on the Atlantic seaboard, and in the Southwest are 

 infrequent, yet occasionally the damage is severe ; while in the 

 two regions previously mentioned as more severely visited, the 

 losses are more nearly annual, and the entire crop may occa- 

 sionally be destroyed. 



Symptoms. The idea generally prevails that the leaf curl oc- 

 curs only upon leaves and young branches, but the flowers and 

 young fruit are likewise subject to attack. Since in the latter case 

 the deformations are less conspicuous, and dropping of the parts 

 affected is more prompt, it has often escaped attention. Leaves 

 of the peach affected by this fungus may be detected as soon as 

 the leaf buds have become slightly upfolded. The coloring of the 

 young leaves is somewhat heightened, and as they unfold a curl- 

 ing and arching of the blades becomes prominent. The distortion 

 may be confined to a small area on one leaf as one extreme, or it 

 may occur on all leaves and petioles, as well as on the young stem 

 which bears these (Fig. 64). As the leaves mature the green or 

 reddish color is lost and the hypertrophied areas become pale or 

 slightly discolored. Diseased shoots may attain more than twice 

 their normal diameter and become pale in color. Further changes 

 in the external appearance have been noted in a gray or mealy 

 appearance of the surface, which occurs as a result of the produc- 

 tion of the fungus superficially. Later the affected leaves turn 

 brown and are finally defoliated. When defoliation is extensive 

 the fruit crop will either be lost entirely or so stunted as to be of 

 little value. Under favorable conditions a new crop of leaves will 

 be promptly developed, but there is little or no evidence that this 

 second crop of leaves may be affected even to a very limited ex- 

 tent. Gummy exudations sometimes appear on the enlarged twigs, 

 particularly when the enlargement is not terminal. In case the 

 terminal bud is not affected it may continue to grow later in the 

 season, thus leaving the injured or swollen portion at the base of 



