Sulfur dioxide gas injury to fruit trees. VI

Abstract

1. Leaf fall of Satsuma orange trees (Citrus unshu) as induced by the sulfur dioxide fumigation particulary after the sulfur containing sprays such as lime sulfur was studied with 2-year-old potted plants. Fumigation was conducted with 0, 1, and 5ppm of sulfur dioxide for 3 weeks 2 hours each day, in December.2. Sodium sulfide (0.4% water solution) had the worst influence on leaf fall, and it was followed by wettable sulfur (0.4% water suspension). The higher the concentration of lime sulfur, the more increased the leaf fall with the fumigation of higher concentration of sulfur dioxide. Namely, it is suggested that spray of lime sulfur from autumn to winter with practical concentration would be safety unless the sulfur dioxide concentration be not markedly high.3. Kinetin (20ppm in 20% ethanol solution) had no effect to prevent the leaf fall due to sulfur dioxide fumigation in winter.4. Increase of sulfur content of leaves as indication of infiltration of sprays was generally low, though in the lime sulfur spray of Be 1.4° was the highest. Sodium was the highest in the sodium sulfide spray among the treatment, but sulfur suffered no change in this spray. Therefore, the promotion of leaf fall due to sulfur containing sprayss with sulfur deoxide fumigation would be caused by infiltration of sprays, but not be always by sulfur.