132 



one hundred and fifty g-allons of water) applied at this season may 

 destroy practically all leaf-crutnplers in time to prevent noticeable 

 damag-e by them. 



The Peak-leaf Blister.* 

 lyEn'op/iycs pyri ) 



This is a blemish of the pear-leaf, appearing- first as reddish 



blister-like spots an eighth of 

 an inch or more in diameter 

 (Fig-. ]8),andg-radually chang- 

 ing-, through green, to black 

 corky spots (Fig. 19), often so 

 abundant as to destroy the 

 larger part of the affected tis- 

 sue of the leaves. It is caused 

 by minute four-legg-ed mites 

 which live within the substance 

 of the leaf and pass the winter 

 in the bud scales at or near the 

 ends of the twigs. In this sit- 

 uation they are of course cer- 

 tain to be sold with the tree, 

 and delivered alive to the cus- 

 tomer. 



They may be destroyed by a 

 thorough spraying with kero- 

 sene emulsion diluted to con- 

 tain about ten per cent, of 

 kerosene. 



The leaves of an infested 

 tree are likely to show the pres- 

 ence of this disease before they 

 fully open in spring-. In this 

 earliest stag-e red blister-like spots appear on the young leaf, 

 brig-htest on the upper surface. Later they change through green 

 to brown, becoming- finall}^ dark brown or black, reaching this last 

 condition about the middle of June and continuing then unchanged 

 until the fall of the leaf. These black spots are dead and dried 

 and often unite to form large blotches, sometimes covering the 

 greater part of the leaf. The new growth of the summer is likely 



*Fora full, illustrated paper on this injury see especially an article by Professor 

 M. \'. Slingerland in Bulletin 6i of the Cornell University Agricultural Experi- 

 ment Station, December, 1893 pp. 317-328. 



18. The Pear-leaf Blister ; 

 earlier stage (spots red- 

 disli). 



