Melville and Hardesty (104) applied calcium nitrate and boron sprays in | 
three orchards in a season of severe bitter pit. Varying, but encouraging, 
results were obtained with calcium nitrate sprays. No benefit was found from 
boron sprays. 
Smock, Fisher, and Forshey (153) applied boron and calcium sprays to 
Baldwin, Northern Spy, and Rhode Island Greening. Boron and calcium acetate 
sprays failed to reduce bitter pit. Calcium nitrate and calcium chloride 
sprays, however, reduced bitter pit, in some tests highly significantly so. 
They state that the present thinking is that pitting is probably induced in 
the orchard by competition between leaves and fruits for calcium. It is appar- 
ently not a simple calcium deficiency problem, but a complex relationship be- 
tween elements like calcium, magnesium, potassium, and nitrogen. 
Chittenden (41) applied foliar sprays of the acetates of sodium, potas- 
sium, calcium and magnesium, sodium borate, and iron chelate to Cox's Orange 
Pippin. Calcium and magnesium acetate slightly reduced the incidence of bitter 
pit, but potassium and sodium acetate greatly increased pitting. Borax and 
iron chelate very slightly increased pitting. Ground limestone at 4 tons per 
acre increased pitting, but gypsum applied at the same rate had no effect. 
Beyers (20, 21), in South Africa, found calcium nitrate and calcium 
chloride equally effective in reducing the incidence of bitter pit. Best re- 
sults were obtained with three sprays of calcium nitrate, at 14-day intervals, 
beginning in mid-December for Golden Delicious and Starking and beginning in 
early January for White Winter Pearmain,. 
Jackson (74, 75) tested sprays containing calcium, magnesium, potassium, 
phosphate, nitrogen, iron, strontium, tungsten, and vanadium. Only calcium 
nitrate significantly reduced the incidence of bitter pit during storage. Both 
tree sprays and postharvest fruit sprays of this compound consistently reduced 
the disorder. Later sprays tended to be more effective than early ones, but 
the most effective treatment was calcium nitrate (6 pounds per 100 gallons of 
water) applied at 14-day intervals throughout the season. No damage occurred. 
Hilkenbaumer and O'Daniel (69) found a marked decrease in bitter pit 
and decay, after storage, in apples from trees sprayed with 0.2 to 1.0 percent 
calcium nitrate and 1,0 percent calcium chloride. Two sprays of calcium 
nitrate, the first applied 4 weeks before harvest gave the best results. 
Van Schreven and associates (173) were able to reduce bitter pit by 75 
percent in Cox's Orange Pippin by five applications of calcium nitrate. A 
postharvest dip in a solution of 0.75 to 1.0 percent calcium nitrate reduced 
pit by only 30 percent. 
Buchloh (31) reported that spraying trees with calcium nitrate reduced 
the incidence of bitter pit to 6 percent, whereas a fruit dip in a 1 percent 
solution reduced the incidence of bitter pit only to 41 percent compared to 71 
percent in untreated fruits. 
Baxter (14, 15, 16) has published an excellent review of bitter pit and 
also an account of his work in Australia where bitter pit is most prevalent on 
Cleopatra, Delicious, and Gravenstein. 
In all cases, calcium sprays were effective in reducing bitter pit at 
harvest, and if the sprays were also applied shortly before harvest, they were 
effective in reducing pit in stored fruits. Calcium nitrate slightly delayed 
maturity and reduced the red color of the apple, so that for red varieties cal- 
cium chloride is recommended. Soil application of calcium nitrate was less 
effective than sprays in the control of bitter pit, but a combination of both 
appears superior to the use of sprays alone. 
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