FOLIAR CALCIUM SPRAYS REDUCE APPLE BITTER PIT 

 Mack Drake, W. D. Weeks, J. H. Baker, D. L. Field and G. W. Olanyk''- 



Bitter Pit disorder of apples was recorded in Germany in 1829 and 

 1862, and was officially recognized in Australia in 1892. Bitter pit 

 (also called stippen, Baldwin spot, or fruit spot) occurs where apples 

 are grown throughout the world - Europe, Australia, New Zealand, South 

 Africa, Japan, Northeastern U.S.A. and Canada, etc. Some of the more 

 susceptible varieties are Baldwin, Northern Spy, and Cortland in North- 

 eastern U.S.A. and Canada; Golden Delicious, Red Delicious, Starking, 

 Jonathan, Winter Pearman in South Africa; Sturmer, Cox's Orange Pippin 

 and Cleopatra in Australia and New Zealand. 



Physical Characteristics of Bitter Pit 



South African scientists divide bitter pit into "tree pit" and 

 "storage or store pit", which is reduced by calcium foliar sprays, and 

 "confluent pit" found in fruit at harvest - this latter was not reduced 

 by calcium sprays. It is thought that pitting is induced in the orchard, 

 but in some cases it may not develop until the fruit is in storage. 

 Maximum storage pit developed in Australia and South Africa when fruit 

 from susceptible trees was picked 2 to 3 weeks early - before the dis- 

 order had fully developed on the fruit. Often it is a hidden disease 

 because fruit free of pit at harvest may develop pits during storage. 

 Bitter pit, not to be confused with internal corky abnormalities, such 

 as boron deficiency - is characterized by brown depressed spots approx- 

 imately 0.2 inches in diameter in the fruit flesh immediately under the 

 skin. In the most susceptible varieties, a greater number of spots ap- 

 pear near the calyx end. 



Smock, in New York, stated that in early stage of development, 

 groups of cell walls beneath the inner skin (hypodermal) of the fruit 

 collapse. Initially, neither the inner (hypodermis) nor the outer skin 

 (epidermis) are affected, but in advanced development, the walls collapse 

 and become torn. With the collapse of large areas of fleshy tissue just 

 beneath the surface, both inner and outer skin tissues become distorted, 

 are depressed and turn brown or black (Figure 1), spoiling the apple's 

 appearance. The pitted areas are not removed by automatic peelers in 

 processing, and apples with the bitter pit disorder are not acceptable 

 in the better grades of fruit. 



Value of Balanced Mineral Nutrition . A high level of nitrogen, low 

 calcium, small crop set, large fruit size, heavy pruning and moisture 

 stress, are reported to increase the fruit's susceptibility to bitter 

 pit. Research during the past decade shows that bitter pit development 

 is related to low calcium content of leaf or fruit. Martin, from Aus- 

 tralia, reports nearly twice as much calcium per cell for sound as for 

 pitted fruit. Kidson and coworkers, in New Zealand, show that the cal- 



Professor, Associate Professor, Assistant Professor and Technical Assist- 

 ants, Department of Plant and Soil Sciences, University of Massachusetts, 

 Amherst. 



