Influence of Sulfur Dioxide and Hydrogen Fluoride as a Mix or Reciprocal Exposure on Citrus Growth and Development

The influence of exposure to mixtures of SO₂ and HF on Koethen sweet orange and mixtures and alternate exposure to these gases on Satsuma mandarin were tested using a rotating fumigation greenhouse. Effects of HF-SO₂ mixtures on linear growth and leaf area of Koethen orange were additive, not synergistic. No necrosis was observed on Koethen oranges exposed to HF, SO₂, or a mixture of HF and SO₂. Effects of the mixture on chlorosis of Satsuma mandarin foliage was also not synergistic. No significant difference in linear growth of Satsuma mandarin was found among all treatments. Alternate exposure to SO₂ followed by HF produced no synergistic injury to Satsuma mandarin. Satsuma mandarin appeared more sensitive than Koethen orange to HF, SO₂, and mixtures of these two gases using degree of chlorosis and leaf abscission as the criteria of sensitivity. If iinear growth and leaf area were the principal criteria considered, Koethen orange would appear more sensitive.