MARKET DISEASES OF FRUITS AND VEGETABLES 63 



Silicate Injury 



On certain varieties of pears, both on the market and in cold 

 storage, a brown spotting that is different in some respects from 

 that caused by rubbing or bruising was a problem some years ago. 

 It was often found on pears that had been in contact with corru- 

 gated-paper lining the boxes or with excelsior-filled pads used in 

 boxes to prevent bruising. 



In some of the corrugated paper used for lining pear boxes, 

 sodium silicate has been used as a binder to hold the corrugated 

 and the flat sheet together. Some grades of silicate contain a small 

 percentage of free alkali, and there is abundant evidence that this 

 is the constituent that caused the injury. Moisture was necessary, 

 and in many instances it seemed to be present in sufficient amounts 

 within boxes packed with pears to cause some of the alkali con- 

 tained in the paper liners to go into solution and produce injury. 



The spotting was brown and usually only superficial and was 

 most pronounced on russeted areas of the skin. It sometimes oc- 

 curred in bands crosswise of the fruit, corresponding to the cor- 

 rugations in the paper liner, but usually it appeared merely as 

 irregularly shaped brown spots % to 1 inch in diameter. Varieties 

 on which it was found are Winter Nelis, Bosc, and P. Barry, all of 

 which showed more or less russeting. It was not found on smooth- 

 skinned pears, although a dark discoloration on Anjou pears, 

 the result of pressure or rubbing against the paper liner, the box, 

 or other pears, was sometimes confused with it. 



Silicate injury seems to have no effect on the keeping quality 

 of the fruit. The spotting can be avoided by using liners that do 

 not contain free alkali from sodium silicate or any other source. 

 Apparently the conditions causing silicate injury have been cor- 

 rected. 



(See 117.) 



Sooty Blotch 

 (See Apples, Sooty Blotch, p. 52.) 



Spray Injury 

 (See Apples, Spray Injury, p. 53.) 



Stigmonose (Insect Punctures) 

 (See Apples, Stigmonose (Insect Punctures), p. 54; pi. 4, G, 

 H.) 



Stony Pit, Corky Spot, and Boron-Deficiency Pitting 



Three kinds of pits found on pears are at first sight so similar 

 in appearance that they are often confused. These are stony pit, 

 corky spot, and pits resulting from boron deficiency. 



Stony pit is common in pears of the Bosc variety, and major 

 commercial losses caused by it appear to be limited to that 

 variety. It is also found in pears of the varieties Winter Nelis, 

 Anjou, Hardy, and Forelle; but losses in these are generally 

 negligible. Stony pit is widely distributed, probably wherever the 

 Bosc variety is grown. In the United States it is not known to 



