24l' NEBRASKA STATE HORTICULTURAL SOCIETY. 



young trees and should be carefully watched for in all nursery 

 stock. 



How spread: As long as we do not know the cause we can not 

 tell how it is spread. It is undoubtedly spread from orchard to 

 orchard while the trees are young by planting affected trees. 

 The disease also spreads from tree to tree in the nursery. W. 

 B. Alwood of the Virginia Station says: 



"The organism undoubtedly attacks the seedling apple trees 

 in the nursery. The organism gaining entrance to the radicle 

 or main root stock soon after germination, by entering through 

 one or more of the main root hairs." 



HEART ROT. 



Cause: There is much difference of opinion as to the cause of 

 this disease, but it is certain that some pore fungus causes 

 the trouble. The threads of these larger fungi are found ram- 

 ifying through the tissue. 



Deso'ipt'ion: There are two kinds of heart rot. In one case 

 the heart wood becomes soft, punky, and brown and is known 

 as wet rot; in the other case it becomes dry, brittle and white, 

 and is known as dry rot. The tree, when the disease is well 

 advanced, is easily snapped off by the wind, or broken by any 

 small force. The processes of nutrition are stopped and the 

 tree dies. The fruits of the fungus are produced on the tree 

 trunks in the form of brackets, but do not appear until the dis- 

 ease is well advanced. 



How spread: The spores borne on the brackets are carried by 

 the winds and insects to other trees, where they germinate 

 and enter the tree through any wound they may find. 



Treatment: Great care should be exercised in the manage- 

 ment of the orchard to prevent wounds. In pruniug, or when 

 the trees are injured in any way, the wound should be painted 

 or covered with wax. The fruits should be destroyed as soon 

 as they appear, and as soon as the tree is so badly affected as to 

 be worthless, it should be removed from the orchard and burned. 



POWDERY MILDEW. 



Cause: Powdery mildew is caused by a sac-fungus {Podos- 

 phaera oxycantha) which grows over the surface of the leaves 



