Studies on magnesium deficiency of apple trees. III

Abstract

The appearance of interveinal leaf blotch with subsequent necrosis and defoliation of apple trees have been increasingly observed in many commercial orchards since the last 10 years, and there is some consequent loss of production from affected trees. The symptoms of this necrosis and defoliation in the field seemed to be the same as those described for magnesium deficiency by many workers, although interveinal chlorosis or fading of the leaves were not prominent under the conditions in Aomori PrefectureThe present investigation was undertaken to diagnose this early season′s defoliation of Ralls trees by means of injection and foliar spray of magnesium solution, and to see the changes of potassium, calcium and magnesium contents in leaves from different position of shoots that has received magnesium treatment.Injections of 0.05M magnesium solutions, during early-May to early-June, 1962, into the trunks of 8-year-old Ralls trees have markedly prevented the incidence of defoliation. A treatment consisting of 10 applications of 3 per cent Epsom salt spray at 7-10 day intervals starting after petal fall has completely prevented the appearance of defoliation of the Ralls trees. It is concluded from the results of experiment and diagnosis of the symptoms that this necrosis and defoliation are due to the deficiency of magnesium in the trees.Analysis of samples (without petioles) collected from mid-shoot leaves of injected trees showed that magnesium content in the leaves increased slightly, but significant correlation was observed between quantities of injected magnesium and leaf magnesium contents, and more close correlation was found as the season progressed. Salts containing nitrogen, calcium and phosphorus were also injected with magnesium sulfate solutions, but they gave no supplementary effect on deficiency incidence and on leaf composition.Foliar applications of magnesium markedly increased the magnesium content in basal leaves of the shoot than that in apical one, and some visual damages of basal leaves, which closely resembled to magnesium deficiency symptoms, seemed to be caused by extreme accumulation of magnesium by frequent spray treatments. The foliar applications of magnesium induced significant depression of potassium and calcium contents in both apical and basal leaves of the shoots.Comparisons of total cation contents(K+Ca+Mg) between sprayed and control leaves, expressed as milliequivalent per 100g dry matter, have shown that sum of total cation contents in an individual leaf varied widely by spray treatment, time of sampling and leaf position, whereas the mean value of total cation contents from entire leaves on a shoot was nearly constant.