488 INSECTS AFFECTING VEGETATION 



DISEASES OF SMALL FRUITS. 



Anthracnose of Berries Nature and Cause. This disease 

 which is commonly known by the popular name of anthracnose, 

 is caused by a very small form of fungus (Gloeosporium venetum). 

 consisting of two parts the mycelium and the spores. The way 

 in which the fungus passes the winter is not known. It probably 

 lives in the canes and fragments of leaves that remain in the field 

 after pruning is done. From field observation on the blackberry, 

 the disease attacks the stems, leaves and fruit during the spring. 

 The spread of the disease is caused by the distribution of the spores. 

 Some of the spores lodge on the host plants. When the climatic 

 conditions are favorable, the spores germinate and form the my- 

 celium, which penetrates the tissue of the stems, leaves and fruit, 

 causing spots on them. The mycelium soon gives rise to a large 

 number of short branches just beneath the thin outer coat (epi- 

 dermis). Spores are borne on these branches. When they form, 

 they cause the epidermis to break open. These spores are held 

 together by a mucilaginous substance which is soluble in water. 

 In the presence of moisture, the spores are set free and are carried 

 about by the wind and other agents. Some of them are sure to 

 lodge on the various parts of the host plant. 



The spots in the stems of plants affected are found to be 

 elliptical in shape and have somewhat irregular margins. They 

 vary in size from less to three or four times larger than a pin head 

 usually about twice as large. The center is a light grey to 

 nearly white in color, while the margin is a deep brown. When 

 these spots are mature in size they are sunken, and oftentimes split 

 open lengthwise with the cane. They usually extend nearly 

 through the bark. When abundant, irregular patches of consider- 

 able depth are formed, which act as a partial girdle on the stem. 



The spots in the leaves are round and smaller than those in 

 the canes usually about half as large as the head of a pin. The 

 centers are nearly white in color, while the borders are wider and 

 of a reddish-brown color. These spots usually extend through the 

 leaf, and when they are abundant run together, forming large 

 patches. These dead areas drop out, leaving holes or slits in the 

 leaves, causing them to appear as if whipped by the wind. The 

 injury done the stem and leaves is very little as compared with 

 the injury done the fruit. 



When young drupels become infested, a small brown dot ap- 

 pears on the surface on the end. These areas increase rapidly in 

 size and soon involve the entire surface. In the meantime, the in- 

 fested portion stops growing, the surface becomes rough and 

 marked with nearly white lines, caused by the epidennis splitting 

 open. As the fruit matures and the amount of water increases in 

 them, the infested areas become more or less shrunken. The spot 

 becomes deeper brown in color. The center of each may become 

 white, owing to the development of masses of spores. At this stage 

 the fruit is nearly red in color, and the spots are very conspicuous. 



