THE DISEASES OF FRUITS. 231 



Remedies. Owing to the fact that the fungus lives from year 

 to year in tae growing layer of the branch, it is evident that 

 when once a tree is infested, ordinary spraying is not effective 

 as a cure. The only successful method of treatment thus far 

 determined is the knife and saw, by which the diseased parts 

 are removed, care being taken to cut several inches below any 

 signs of the knot, or otherwise a new excrescence will form 

 upon the stump. The spores are abundant in such knots, and 

 they need to be burned, for if thrown into a brush heap the 

 germs will escape as well from there as when upon the tree. 

 All similar knots upon wild plants should be treated in the 

 same way, and this is not the only case where the fruit grower 

 needs to go beyond the garden fence to stay an enemy lurking 

 close at hand. 



Experiments have been made with some success in checking 

 the fungus by using fungicides. Spraying at a time when the 

 trees are most susceptible in early spring, and the painting of 

 the knots with a destructive liquid, have given some encour- 

 agement ; but the only reliable method thus far suggested is 

 that of cutting away the diseased parts as soon as they are 

 found by careful search. 



Plum Pockets {Exoascus pruni Fcl.) are well named abnormal 

 fruits that become many times their natural size and usually 

 very spongy and often hollow (see Fig. 289). The same 

 fungus attacks the twigs sometimes so extensively as to de 

 stroy all the young branches. These affected tips become like 

 the young fruits above noticed, and dying give the tree an ap- 

 pearance similar to that caused by the fire blight upon the 

 apple. The " pockets " are often abundant during moist or 

 wet springs, and some varieties seem more susceptible than 

 others. 



Remedies. Experimental tests for the control of this fungus 

 have not been extensive, and while spraying may prove suc- 

 cessful it can only be suggested for trial. The fungus is of 

 the same class as that causing the black knot, and like it may 

 require the heroic method of severe pruning. As the Exoascus 

 attacks the young portions, the removal of the parts is an easier 

 matter than with the black knot, especially if the latter has 

 been upon the tree for some years. ^ 



The Leaf Blight (Cylindrosporium /W/Karst) produces brown 



