MARKET DISEASES OF APPLES, PEAES, QUINCES 53 



one pear to another in such a manner that the rotting fruits are 

 held together, and it is often possible by careful examination to 

 trace the development of large clusters to a single initial rotten 

 pear (pi. 15). Gray-mold rot is darker brown in color than blue- 

 mold rot and the affected tissue is relatively much firmer. It usually 

 has a sour smell. 



The casual organism {Botrytis sp.) is widely distributed and lives 

 upon a large number of hosts. It is present on decaying matter in 

 the orchard, a circumstance that probably is responsible for much 

 of the infection found in stored fruit. Infection frequently takes 

 place through the stem, starting at the free end. Diseased stems 

 become soft and spongy, and in advanced stages of the decay can 

 be crumbled between the fingers. When pears for storage are not 

 packed immediately after picking, special care should be exercised 

 to sort out any with partially decayed stems or to cut these off below 

 the affected part. Prompt cooling of the fruit reduces the serious- 

 ness of the disease, but Botrytis is able to continue its growth and 

 produce decay at the usual cold-storage temperature of 32° F. 



Good packing-house sanitation and careful handling of the fruit 

 to prevent abrasions and bruises are of value in preventing the de- 

 velopment of the disease later in storage. The most practical method 

 of preventing the spread of the rot from one fruit to another is the 

 use of copper-treated wrappers, and this discovery promises to be 

 of great value in reducing the losses from the disease. The wraps, 

 if treated with soluble copper compounds such as copper sulphate, 

 may cause injury if the pears are wet when packed. The injury is 

 exhibited bv irregularly shaped black spots scattered over the sur- 

 face of the fruit (pi. 18, E). (44, 4^', H-) 



PEAR-LEAF BLISTER-MITE INJURY 



{Eriophyes pyri Pgst.) 

 OCCURRENCE, SYMPTOMS, AND EFFECTS 



Two types of injury by the pear-leaf blister mite may be found on 

 pears and also on apples: A diffuse russeting, usually most marked 

 at the calyx end, and irregularly shaped, depressed, brown russeted 

 spots one eighth to one half inch in diameter, most of which are 

 eventually surrounded by a zone of almost decolorized skin (pi. 19, F) . 

 Severely infested fruit may be considerably distorted. This mite is 

 widely distributed over the United States, but on the market the 

 injury is seen most often on fruit from the West or Northwest. 



CAUSE 



The blister mites are microscopic in size, elongate in shape, and 

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

 appear on the foliage as soon as it unfolds. The activities of the 

 mites result in the development of small, blisterlike swellings, which 

 later become brown and dry, giving an appearance of spotting sim- 

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

 damage is to the foliage, the blossoms and young fruit are also 

 attacked. 



