ORCHARD INSECTS OF THE PACIFIC NORTHWEST 



21 



times to crack open. The mites also injure and deform the blossoms. 

 There is some evidence that the mites attacking apple and pear are dis- 

 tinct species, since very often one fruit shows evidence of injury, while 

 on adjacent trees the other fruit does not. The mite that attacks 

 the apple apparently comes from the wild snowberry (Symphori- 

 carpos racemosus 

 Michx.), since a mite 

 that seems to be 

 identical is found on 

 that plant, and in- 

 fested apple orchards 

 are most often in 

 canyons and along 

 foothills adjacent to 

 wild growths of the 

 snowberry. The 

 form found on the 

 pear tree is evidently 

 the same as the spe- 

 cies occurring in 

 Europe, and un- 

 doubtedly came from 

 there originally. 



-Apple deformed and russeted by pear leaf 

 blister mite. 



LIFE HISTORY 



The adult mites 

 pass the winter un- Figure 22. 

 der the scales of fruit 

 and leaf buds. They 



are exceedingly small, less than one one-hundredth of an inch in 

 length, and are therefore practically invisible to the naked eye. 

 Under a lens or a microscope they appear (fig. 23) as elongated, 

 whitish, wormlike creatures, with four legs near the head end. Often 

 hundreds of them can be found in a single bud. When the buds 

 begin to swell under the influence of warm spring weather, the mites 

 lay eggs in them, and the young hatching from the eggs burrow into 

 the unfolding leaves and form the characteristic 

 blisters. Th e mites feed entirely within the blisters, 

 and a succession of generations develops, prac- 

 tically out of the reach of sprays. With the ap- 

 proach of cold weather the mites migrate to 

 Figure 23.— Adults the bud beneath the sca i es f wmch they hiber . 

 or the pear leaf , J 



blister mite. X 40. nate. 



CONTROL 



The pear leaf blister mite can be controlled very easily with lime- 

 sulfur solution used as a dormant spray at the same strength as for 

 the San Jose scale; that is, a solution testing 4%° Baume (table 1, 

 p. 71). If the San Jose scale is not present, the solution need test 

 only Sji Baume. Spraying should be completed in the spring before 

 the buds have begun to open, for the mites get into the leaves soon 

 after that and cannot be reached with the spray. Good control may 

 also be obtained by spraying in the fall, as soon as the leaves have 

 dropped. Oil emulsions are not very effective unless applied just as 



