Effects of silicone antitranspirant on woody plants

Abstract

Effects of Dow Corning silicone emulsion antitranspirant (XF-4-3561 Fluid) on transpiration of Fraxinus americana, Acer saccharum, and Pinus resinosa seedlings and on chlorophyll content and seedling mortality of these species and Pinus strobus were investigated. The effect of silicone on expansion of new (current year) needles of Pinus resinosa and P. strobus was also studied. Transpiration of Fraxinus seedlings treated with 1, 3, 5, 8, or 10% silicone was reduced for only one day. Five and 3% silicone reduced transpiration by about 70% and 40% in Acer. The effects of 5% silicone lasted at least 7 days and of 3% silicone for about 5 days. Five percent silicone decreased transpirations of Pinus resinosa by 90% for more than 10 days in plants growing in wet or dry soil. Internal water balance of Pinus resinosa needles was improved 12 days after treatment with 5% silicone. Silicone emulsion at 50, 20, and 10% was toxic to all four species. Fifty percent silicone killed all four species. Twenty percent silicone killed Acer and Pinus resinosa seedlings, and caused shedding of whole leaves of Fraxinus. Ten percent silicone induced brown spots (about 1 mm in diameter) on Fraxinus leaflets, browning at tips of Acer leaves, and a light green color at tips of new (current-year) needles of Pinus resinosa and P. strobus. Acer leaves treated with 10% silicone suddenly turned brown on a hot day, indicating that weather conditions greatly affected appearance of toxicity symptoms. Silicone at 1 or 3% did not induce injury to any of the four species investigated. Elongation of new (current-year) needles of Pinus resinosa and Pinus strobus seedlings was significantly retarded by 20 and 10% silicone. The growth rate of new needles of Pinus strobus during the second month after treatment with 10 or 20% silicone was higher than that of plants treated with 3 or 1% silicone or of control plants. Three percent silicone also retarded growth of new needles of Pinus resinosa. Chlorophyll content 45 days after application of 20% or 10% silicone was reduced in all 4 species. Three percent silicone reduced chlorophyll content in Pinus resinosa and Acer saccharum, but not in Fraxinus or Pinus strobus. One percent silicone did not reduce chlorophyll content in any species. Possible reasons for variations in species response to silicone are discussed.