A Bulletin on Orchard Practice 19 



nearly black. They increase slowly in diameter but the fun- 

 gus penetrates the bark into the sap wood beneath. When the 

 tree begins to leave out the cankers increase rapidly in diam- 

 eter and are mature in size by the last of -June or a little later. 

 Mature cankers are usually oblong and vary in size from % 

 of an inch to 6 inches long by % of an inch to 5 inches in 

 width. Frequently they appear to be 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 brit- 

 tle and separates from the living, leaving a fissure. It re- 

 mains on the tree for a time and then falls out, leaving a 

 scar. 



About the time the cankers are full grown the epidermis 

 (skin) on the cankers become slightly roughened by the for- 

 mation of pustules just beneath it. Each of these pustules 

 contains numerous spores which when distributed 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 that the way to pre- 

 vent the disease is to prevent the germination of the spores. 

 This can be done by spraying the trees with double strength 

 Bordeaux mixture about the first of November to kill the 

 spores on the bark. Under ordinary weather conditions there 

 will be sufficient spray on the bark 'to kill spores that may 

 lodge on it for a short period of time if the work has been 

 done properly. To catch the spores that are distributed later 

 in the season spray a second time with double strength Bor- 

 deaux mixture making the application thorough so that the 

 entire tree is covered with the spray. The second spraying 

 should be done two or three weeks after the first. In rainy 

 weather three or more sprayings may be necessary to keep the 

 bark protected. 



CROWN-GALL AND HAIRY-ROOT. 



A report of investigations by Mr. George G. Hedgcock of 

 the U. S. Department of Agriculture on Crown-Gall and 

 Hairy-Root, indicates that they are two separate and dis- 

 tinct diseases, which is contrary to the belief by some that 

 these are two forms of the same disease. Much remains yet 



