Since 1945;workéers:in the :Netherlands;(1,579,ollljoll2, 11354160; -lol; 
176) have made new tests using sprays of borax a ee reductions in in- 
cidence of bitter pit. This work showed that the time of application of boron 
was critical and reductions occurred only when treatments were applied over a 
short period at about the time of full bloom. Spraying outside this period 
might increase bitter pit (161). On other soil types in the Netherlands, how- 
ever, these results could not be repeated (113). Boron sprays at time of bloom 
did not reduce or control bitter pit in tests conducted in widely separated 
parts of the world by Bould and Tolhurst (25), Martin and Carne (94), Smock and 
associates (153), Southwick (155), and Melville and Hardesty (104). Martin, 
Lewis, and Cerny (97) did not try boron alone but sobs: no benefit by adding 
boron to calcium nitrate sprays. 
After 1945, workers in the Netherlands switched their research from 
boron to other minerals. They confirmed Brown's (30) observation that fruit 
with bitter pit had a low phosphorous content and thought that this was due to 
magnesium deficiency (113, 114, 115, 116). Later, Netherland workers reported 
that bitter pit was associated with high potassium content of the leaves (160, 
162) and fruits (171). 
Continuing this review Martin states, "Dunlap and Thompson found that 
sprays of boron applied at full bloom gave a response, but there is doubt that 
the disorder in this case was similar to that recognized as bitter pit in 
Australia" (46). (See Cork Spot.) 
The real turning point in gaining a measure of understanding and control 
of bitter pit started with investigations on the relation of calcium to the 
disorder. This came about slowly following the unexpected results of DeLong in 
1937 (44). He analyzed the ash content of apples affected with "blotchy cork," 
a type of bitter pit. At the time of the analysis, emphasis was on the newly 
discovered boron deficiency. It was thought that perhaps a high calcium content 
was preventing assimilation of boron and thus causing bitter pit. Instead, the 
affected apples showed a low calcium content. About 20 years later a study was 
made on calcium deficiency in relation to bitter pit. 
This study was made by Garman and Mathis (56) on the effect of calcium 
on "Baldwin spot" (bitter pit). They reported that the disorder was related to 
an unbalanced nutritional condition. They concluded that calcium was the 
critical element and that an imbalance between calcium and magnesium or between 
these and potassium was definitely related to the occurrence of bitter pit. 
They also found a definite connection between the amount of bitter pit and the 
leaf to fruit ratio of calcium. They state that excess nitrogen can easily 
prevent a favorable balance through promotion of increased potassium and mag- 
nesium in the fruit. They stated that efforts to control bitter pit through 
calcium sprays were partly successful, but that much more research was needed. 
A considerable amount of research was stimulated by their discussion of unbal- 
anced nutrition and bitter pit. 
In 1960, Martin, Lewis, and Cerny (97) studied the effect of calcium 
and magnesium sprays on the occurrence of bitter pit in the Cleopatra (Ortley) 
variety. They found that magnesium nitrate increased pit, whereas, calcium 
nitrate decreased it. Calcium dihydrogen phosphate had no significant effect 
with or without borax. They indicated that borax may have reduced the effec- 
tiveness of calcium nitrate. They agreed with Garman and Mathis (56) that 
calcium was the critical element and that an unbalanced condition lies between 
calcium and magnesium. There was, however, no evidence from their results that 
potassium or phosphorous were involved. 
168 
