MARKET DISEASES OF FRUITS AND VEGETABLES 61 



CAUSE 



Blister mites are microscopic in size and elongate in shape and 

 have only two pairs of legs. They hibernate under bud scales and 

 appear on the foliage as soon as it unfolds. Their activities result 

 in the development of small blisterlike swellings, which later 

 become brown and dry, giving an appearance of spotting similar 

 to that caused by leaf spot fungi. Although the most serious 

 damage is to the foliage, blossoms and young fruit are attacked. 



CONTROL MEASURES 



The blister mite can be controlled by thorough spraying during 

 the dormant period with winter-strength lime-sulfur, as for San 

 Jose scale. Oil sprays applied during the dormant season are less 

 satisfactory, although fairly good results have been obtained by 

 using them in warm periods in the spring after the buds have 

 begun to swell. 



(See 93, 101.) 



Pear Psylla Injury 



(Psylla pyricola Foerst.) 



Pears injured by the pear psylla are black as a result of the 

 growth of a black fungus on the honeydew produced by the in- 

 sects, which also cause serious injury to foliage and young growth. 

 The psylla is a tiny cicadalike insect, about y 10 inch long when 

 full-grown. Adults hibernate in cracks in the bark of tree trunks 

 and limbs, under bark scales, or under trash on the ground in 

 and near orchards and migrate to the trees on the very first warm 

 days of spring. Applications of 3-percent lubricating-oil emulsion 

 at this time have given very satisfactory results. They kill many 

 of the adult flies, and the film of oil on the bark appears to have 

 a great deal of residual value, reducing the number of eggs laid 

 and killing a high percentage of the young psyllas that hatch. 

 Nymphs of the first brood congregate mostly in the axils of young 

 leaves and fruits and may be treated with a nicotine-soap spray 

 applied just after the blossoms fall. 



Pink Mold Rot 

 (See Apples, Pink Mold Rot, p. 42; pi. 7, B.) 



Powdery Mildew 



(See Apples, Powdery Mildew, p. 43; pi. 2, D.) 



Rhizopus Rot 

 (See Apples, Rhizopus Rot, p. 44; pi. 13, H.) 



San Jose Scale Injury 

 (See Apples, San Jose Scale Injury, p. 44; pi. 2, C.) 



Scab 



(Venturia pyrina Aderh.) 



Scab on pear (pi. 11, A) is similar to the disease of the same 

 name on apple, although the two are caused by different species 

 of the fungus Venturia. Pear scab usually occurs as larger, rougher 



