34 



ANTHRACNOSE. 



Anthracnose (Sphaceloma ampelinum De By.) has also been called 

 "bird's-eye rot," on account of the peculiar spots it produces upon 

 affected grapes. Like most of the other diseases of the grape, it 

 attacks the leaves and shoots as well as the fruit. 

 On the leaves it at first appears as minute, irregular, 

 dark brown, slightly sunken spots, having a darker 

 margin. These spots usually become lighter colored 

 when old, and frequently crack or fall out, leaving 

 irregular holes in the leaves. This disease presents 

 much the same appearance on the shoots as on the 

 leaves, though the spots are frequently larger and 

 more sunken (fig. 16) . They also tend to run together 

 and form irregular patches. 



The disease is most characteristic and conspicuous 

 upon the fruit. The spots are usually brown at first 

 and surrounded by a narrow, dark purplish margin ; 

 they increase in size and gradually become grayish 

 white and somewhat sunken. Frequently two or 

 more spots unite and cover a considerable part of 

 the berry (fig. 17). The affected tissues do not be- 

 come sortened, as in the 

 case of the downy mil- 

 dew, but the fruit be- 

 comes hard and more or 

 less wrinkled. If only a 

 small part of the berry 

 is affected it may con- 

 tinue to grow, causing 

 the diseased area to rupture and the seeds 

 to become exposed. The bursting of the 

 berries and the exposure of the seeds may, 

 however, be produced by other causes. 



Fig. 17. — Portion of a bunch of grapes, 

 showing the effect of anthracnose. 



such as the powdery mildew and 

 certain physiological disturb- 

 ances. 



On the diseased areas the min- 

 ute spores or germs of the fungus 

 are frequently produced in im- 

 mense numbers. The way in 

 which these spores are borne is shown in figure 18. No special 

 winter form of spore is known to be produced by this fimgus. The 

 fine, thread-like filaments which constitute the vegetative part of 

 the parasite live during the winter in the tissues of the vines and 

 are ready for active growth in the spring. 



The anthracnose is quite widely distributed in this country, but 



284 



Fig. 16.— Grape shoot, 

 showing spots pro- 

 duced by anthrac- 

 nose {Sphaceloma 

 ampeHnum) . 



Fig. 18. — Section of an anthracnose spot, highly 

 magnified: a, Showing the way in which the 

 spores are borne; 6, three of these spores more 

 Iiighly magnified. 



