453 



There are also a number of other organisms which produce Root- 

 rot of fruit trees, but American plant pathologists have given these 

 diseases very little attention. No satisfactory line of treatment can 

 be recommended. (B. 16, Mo. State Fruit Exp. Sta.) 



European Apple Canker. This disease is reported as serious in, 

 the orchards of Europe, and is apparently becoming widely distrib- 

 uted in America. It is not of so common occurrence as the black rot 

 canker, but is more destructive where found. The fungus seems to 

 be dependent upon wounds for entrance to the host tissue. It attacks 

 the inner bark and the cambium, and to some extent the young wood. 

 The mycelium is perennial in the host. As the new growth develops 

 around the wound it is attacked and killed by the fungus; thus a 

 series of ridges may be developed, giving a characteristic appearance 

 to the disease. 



Apple Tree Canker. This fungus is very common on both apple 

 and pear trees and during the past season a number of cankered 

 apple-tree limbs were found on which the injuries were evidently due 

 to its attack. All cankered limbs should be destroyed. Wounds 

 should be thoroughly coated with Bordeaux or paint. (N. H. E. S. 

 B. 144.) 



Blackspot Canker. This is a disease of the apple tree. In im- 

 portance it ranks next to the apple scab. It is very prevalent and 

 destructive in Western Washington in localities where the rainfall is 

 considerable during the latter part of autumn and early winter. The 

 disease is caused by a parasitic fungus. The fungus lives in the bark 

 for about a year and then dies. Before it dies it forms spores the 

 greater number of which are distributed from October to late Decem- 

 ber or a little later. These spores are carried about by the wind and 

 some of them lodge on the bark of apple trees. The moderately low 

 temperature and plenty of moisture usually present in November and 

 later are conditions most suitable for germination. On germinating 

 the fungus enters the bark. Occasionally 'by the end of a week new 

 cankers make their appearance. They are about the size of a pin 

 head circular, somewhat sunken and nearly black. They increase 

 slowly in diameter but the fungus penetrates the bark into the sap 

 wood beneath. When the tree begins to leave out the cankers in- 

 crease rapidly in diameter and are mature in size by the last of June 

 or a little later. Mature cankers are usually oblong and vary in size 

 from y of an inch to 6 inches long by ^ of an inch to 5 inches 

 in width. Frequently they appear to oe much larger. As a rule, 

 these larger ones are the result of two or more smaller ones merging 

 together. The cankered bark becomes dry and brittle and separates 

 from the living leaving a fissure. It remains on the tree for a time 

 and then falls out leaving a scar. 



About the time the cankers are full grown the epidermis on 

 the cankers become slightly roughened by the formation of pustules 

 just beneath it. Each of these pustules contains numerous spores 

 which when disturbed will cause the new cankers to appear. 



Since the spread of the disease is caused by spores and the spores 

 germinate in November it follows the way to prevent the disease is to 



