Poor fruit quality due to boron deficiency was first reported over 40 years ago from Finland and New Zealand.
Since then boron deficiency in apples has been recognized in many other countries including Australia, Austria, Canada, Greece, France, Italy, Japan, Korea, Norway, South Africa, Switzerland and the USA. Apart from shoot dieback, the symptoms most commonly reported are internal and external cork formation in the fruit and the development of small, deformed and cracked fruit; a mild expression of any of these symptoms can markedly reduce fruit quality.
Apart from isolated claims, there has previously been no clear indication that boron deficiency occurs on apples in the UK; this is strange in view of the occurrence of boron deficiency in many other countries where apples are grown.
It was one of the objects of this study to determine whether boron applications to apples in the UK could be beneficial.
Although current research indicates that bitter pit is primarily due to a shortage of calcium in the fruit, past research has implicated not only calcium but also boron.
In fact early work has indicated that bitter pit, which was and probably still can be, confused with external cork, could be cured by boron.
Faust and Shear (1968) in their excellent review of corking disorders noted as many papers reporting beneficial effects of boron on bitter pit as those in which boron was not related to the disorder.
Faust and Shear (1968) and Woodbridge, Wieneke and Fuhr (1973) have suggested that boron applications can improve the mobility of calcium in the apple tree.
Their work indicated that when a tree is marginally deficient in boron, but reasonably well supplied with calcium, boron can have a beneficial effect by promoting calcium movement to the fruit: on the other hand, when boron is in good supply, no beneficial effect can be expected.
One objective of this work on the boron nutrition of apples was to study the effect on bitter pit of sprays of boron (as Solubor, a sodium borate with the approximate composition Na2B8O134H2O) and calcium (as calcium nitrate) applied either singly or combined to fruiting trees of the variety Egremont Russet.
However, in the first year of this trial, a marked reduction was also recorded in the incidence of fruit cracking.
This was surprising in view of the fact that boron deficiency had not been reported previously on apples in the UK and a series of observation trials on the effects of Solubor sprays on