Entomological Department. 



THE PEAR LEAF BLISTER. 



Phytoptus pyri. 



Order Acarina ; family Phytoptidae . 



Reddish blister-like spots an eighth of an inch or more in diameter appear 

 ing on the pear leaves in the spring and changing to black corky spots in July, 

 each with a minute opening in it. 



In Bulletin 23 of this Station, issued in December, 1890, this disease 

 of pear leaves was discussed at some length. It was then realized 

 that the only methods of checking the disease which could be sug- 

 gested were too laborious to be practicable, except where the trees 

 were young or few in number. This need of a cheaper and easier 

 method of fighting this pest has been the subject for experimentation 

 during the last two years. Some of these experiments have been 

 strikingly successful, and we are now confident that this disease, which 

 is alarmingly on the increase in the United States and Canada, can be 

 easily and cheaply controlled. 



As the disease has been studied during an entire season, other phases 

 of it, not before recorded, have been seen. The disease has also 

 appeared in several other localities, and is causing considerable alarm 

 among pear growers, judging from the reports of correspondents. It 

 is the purpose of this article then to I'ecord these new facts, and to tell 

 pear growers how the pest can be easily and cheaply combated. As 

 Bulletin 23 is now out of print, it has also seemed best to again discuss 

 the disease in detail. 



/Symptoins of the disease. — The disease appears on the pear leaves 

 before they are fully expanded from the bud, in the spring, in the 

 form of red blister-like spots an eighth of an inch or more in diameter. 

 During this red stage of the disease, the spots are more conspicuous 

 on the upper surface of the leaves. About June 1, the spots gradu- 

 ally change to a green color hardly distinguishable from the unaffected 



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