DISEASES OF CULTIVATED PLANTS 467 



twigs blacken and dry up as if scorched by fire. Usually blossom 

 blight accounts for a large per cent of the infected points, still occa- 

 sionally twig infection exceeds blossom infection. If the season or 

 conditions are unfavorable for the growth of the organism it may 

 run only an inch or two on the branch or fruit spur and stop. But 

 if the conditions are favorable for the growth of the organism it may 

 cause vital injury. The organism may finally run down into the 

 thick bark of the larger branches and continue to develop during the 

 entire growing season, frequently producing serious wounds on the 

 limbs. These wounds may be extended down the limbs into the 

 body of the tree and finally reach the ground. This disease advances 

 in various irregular ways and it is impossible to know just what 

 form the infected area will assume. A blighted fruit spur may pro- 

 duce a circular spot an inch or two in diameter on the limb, fre- 

 quently, however, such wounds are extended from the lower side of 

 the injury, forming a strip of diseased tissue down the side of the 

 limb, often making it difficult to save the limb. Such wounds are 

 usually soon invaded with various wood destroying fungi, forming 

 large wounds or cankers which weaken the vitality of the tree. The 

 amount of injury done by the organism after it gains entrance to 

 the tissue of the tree depends much upon the condition of the tree. 

 A well-nourished tree which is making a vigorous sappy growth suf- 

 fers severely from blight. The older slow growing trees blight less 

 severely than young vigorous trees. Conditions which favor large 

 crop productions usually furnish the most favorable surroundings 

 for the development of this organism. 



Treatment. From the nature of the disease it is plain that 

 it requires the combined effort of a community to control it. In the 

 older orchards where the organism is well established it will require 

 the most persistent effort to get it under control. However, in the 

 younger orchards or where the disease has not become thoroughly 

 established it will yield to the following treatment ; this treatment is 

 also successfully used in controlling this organism on the apple, 

 apricot, plum and quince: Cut out very carefully and thoroughly 

 all the infected tissue in the fall and winter, being constantly on the 

 lookout for the irregular developed cases where disease extends down 

 much further on one side of the branch than the other. The dis- 

 eased limbs in the iop of the tree at ends of the branches are usually 

 readily seen, but the infection on the larger limbs which are covered 

 with rough bark and on the body of trees are frequently very difficult 

 to detect. A dead water sprout usually indicates an infected area and 

 gum exudate occasionally shows the location of some of the obscure 

 cases. The infected branches should always be removed several 

 inches below any signs of discoloration and the wound on the tree 

 disinfected with some strong disinfecting solution. In extreme cases 

 where the disease has infected considerable tissue on the trunk of 

 the tree, it is almost impossible to save the tree and it is usually best 

 to cut down and burn such trees. (Mo. State Fruit E. S. Cir. 3.) 



Leaf Blight of Pear. This disease has long been known to 

 horticulturists as the leaf blight or scald of pear and as the cracking 



