Chemical investigations on bitter pit of apples

Abstract

Cox's Orange apple trees were sprayed about mid December and mid January with aqueous solutions of the acetates of calcium, magnesium, potassium, and sodium, and of superphosphate and borax to attempt to control bitter pit in the fruit in orchards on two differing soil types. Analysis showed that use of the sprays altered the chemical composition of both fruit and leaves. Both fruit and leaves changed in composition and dry-matter content between mid January and harvest time in February or March, not only in respect of mineral and nitrogen content but also in the amounts of acids and sugars present. In one season the calcium spray highly significantly reduced the amount of bitter pit at Annesbrook orchard, but was not significantly beneficial in the second season. On the Moutere Hills orchard in this second season calcium gave the best results, although not significantly so. Potassium in the three trials was very detrimental, significantly increasing the amount of pitting. Sodium and magnesium were detrimental also. High dry-matter and ash contents and high values of the ratio K/Ca in the fruit were associated with increased amounts of bitter pit Chemical data for leader leaves appear to be more valuable than those for spur leaves for diagnostic purposes; high calcium content and high values for the Ca/K ratio are associated with a reduction in bitter pit in the fruit.