Abstract
To determine the effect of calcium sprays on the occurrence of Jonathan spot and the related spotting disorders, CaCl2, lime water or Ca(NO3)2 were sprayed to Jonathan apple trees 4 times in July and August or 2 times in September (CaCl2 only). The concentration of each chemical applied was; CaCl2…0.38%, lime water…1.2% as CaO, and Ca (NO3)2…0.5%. Details of treatments were shown in Part I of this series of report.The incidence of Jonathan spot was reduced by the sprays of CaCl2, lime water and Ca(NO3)2 as shown in Table 1 and 2. Lime water was the most effective in controlling the disorder, CaCl2 was next, and Ca(NO3)2 was least effective.The calcium content of the peel of fruits from the lime treatment was not higher than that of the CaCl2 treatment (Fig. 2). Generally, the incidence of Jonathan spot was relatively low in fruits where the calcium content of the peel was high. However, disorder incidence did not always increase as the calcium content decreased (Figs. 2 and 3). These results suggest that Jonathan spot is not a simple calcium deficiency disorder. The incidence of Jonathan spot in M orchard was exceptionally severe as compared with other orchards (Table 2). In M orchard, K/Ca ratios of the leaves, fruitlets and mature fruits tended to be higher than in any other orchard (Table 5).We classified the spotting disorders of the surface of Jonathan apples into two main types; Jonathan spot and Jonathan freckle according to Heald (6). Additional spotting disorders other than these two main types were found in this experiment, and were also controlled by the sprays of calcium chemicals (Tables 3 and 4). As in the case of Jonathan spot, lime water tended to be the most effective for these disorders. The results of Jonathan freckle were not shown, as this disorder scarcely occurred one month after harvest, the period of this experiment.Fruit spot caused by a fungus (Mycosphaerella pomi) were also reduced by the sprays of lime water and CaCl2 (Table 6).
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