50 MISC. PUBLICATION 168, U. S. DEPT. OF AGRICULTURE 



cality Stayman is much more susceptible to cracking than York 

 Imperial, and the deep, extensive cracking often causes serious 

 losses. Rain cracking develops after periods of cloudy, rainy 

 weather, when the rates of evaporation and transpiration are very 

 low. During such periods apples may absorb rain water through 

 the skin and this in addition to the supply from the roots permits 

 unusually rapid enlargement of the fleshy cells. The internal pres- 

 sure from the enlarging cells against the surface of the fruit cre- 

 ates a strain that results in cracking. The side of the apple ex- 

 posed to the sun, especially if any abnormal condition such as 

 sunburn or spray injury is present, is the most susceptible to 

 cracking. 



Cracking is similar on Wealthy and Stayman apples. The con- 

 dition occurs so frequently and so seriously on the latter variety 

 that it is often termed "Stayman cracking." Cracking occurs 

 chiefly on the cheeks of the fruit in the form of irregular breaks 

 in the skin and underlying flesh. The breaks vary from almost 

 invisible short slits to cracks V2 inch or more deep that may extend 

 almost completely around the apple. Late in the growing season 

 cracks may originate near the stem and extend out over the cheek 

 in more or less straight lines toward the calyx. Cracks around the 

 calyx basin are rare. The exposed flesh gradually becomes dis- 

 colored and decay follows, often while the fruit is on the tree. 



In York skin crack, the cracks are small and tend to run in a 

 latitudinal direction on the cheek of the fruit. If there is a worm 

 sting, hail scar, or other old injury on the fruit the cracks usually 

 run around this center, more or less in rings. 



The cracks may make a wavy line and vary from being barely 

 discernible to being open as much as y ie inch. At first there is 

 no discoloration except possibly a slight russeting, but as the 

 cracks become older they turn almost black. As the underlying 

 tissues dry out the skin is pulled loose and becomes bleached or 

 grayish. In the late stages of York skin crack the cracks are very 

 numerous on the affected parts of the apple and are likely to be 

 accompanied by wilting. 



York skin crack seems to occur on fruit grown on trees of 

 comparatively low vitality or affected by drought during the 

 growing season. It appears to be worse on light-crop trees than 

 on those bearing heavy crops. There is evidence that the severity 

 of the cracking is increased by late rains that cause the apples 

 to sw T ell rapidly and by late spraying with lead arsenate. 



Apples affected with York skin crack are more mature than 

 normal fruit and should be packed and handled separately on this 

 account as well as because it is practically impossible to sort out 

 all affected apples if they are mixed with the general crop. The 

 cracked skin of these apples renders them susceptible to decay 

 in much the same way as any mechanical injury which breaks the 

 skin. 



HEAT CRACKING 



Heat cracking may be produced by hot washing treatments for 

 removal of spray residues, particularly if dipping tanks or other 

 home-made devices are used. It occurs when a cold, turgid apple 

 is subjected to too long exposure in heated washing solutions. A 



