Pear. 



337 



green, and about the middle of June they appear as irregular 

 brown patches, of varying sizes. The leaves become distorted 

 and unsightly, and redden up early in the fall. 



Treatment. Spray the trees in spring before the buds swell 

 with the Hubbard-Riley kerosene emulsion, diluting with 

 five to seven parts 

 of water. One 

 thorough applica- 

 tion will practi- 

 cally exterminate 

 the insect. 



Psylla (Psylla 

 pyricola, Forst.). 

 Description. 1 

 The eggs of this FIG. 72. - Mite causing pear leaf blister, greatly enlarged. 



insect are laid 



early in spring, during warm days of April, by adults which 

 hibernated during the winter. The eggs are laid in small 

 crevices of the twigs ; they hatch in about two weeks, and pro- 

 duce small flattened nymphs (Fig. 73), which suck the juices of 



the tree. They occasionally 

 appear before the buds have 

 opened, in which case they 

 hide under the bud-scales or 

 under the bark, and wait for 

 the coming of the leaves. 

 They then seek the axils of 

 the leaves and move but little. 

 They secrete large quantities 

 of honey-dew, often being en- 

 tirely covered with it. It runs 

 down the stems of the tree, 

 and is a favorable medium for 

 the growth of a dark fungus 

 which causes the tree to ap- 

 pear as if covered with soot. 

 The absence of this color is a good indication that the psylla is 

 not present. The adult insect (Fig. 74) appears about a month 

 after the egg hatches. It closely resembles a cicada or harvest- 



i See Slingerland, Cornett Agric. Exp. Sta. 1892, Oct. Bull. 44. 

 z 



PIG. 73. Immature form of psylla. 



