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Volatility of the diglycolamine salt of dicamba
Laboratory, the Texas A&M University campus and the Texas A&M Riverside campus near College Station, TX. Rate-response and herbicide volatility data were collected using cotton (Gossypium hirsutum L.) and soybean (Glycine max (L.) Merr.) as test plants. Plants were sprayed with nine reduced rates of the diglycolamine salt of dicamba, the dimethylamine salt of 2,4-D or the butoxyethyl ester of triclopyr so that plant responses could be determined for rate-response curves. Herbicide rates ranged from 4x10⁻¹ to 1x10⁻⁵ times the normal use rates. Injury was recorded at 1,5,9 and 14 DAT using a categorical injury rating scale. Herbicide volatility data was then obtained in the greenhouse using volatility chambers that exposed cotton and soybean plants to herbicide vapor originating from treated bermudagrass (Cynodon dactylus (L.) Pers.) sod placed upwind from the plants. The bermudagrass had been previously treated with 1. 12 kg ha⁻¹ of dicamba, 1.06 kg ha⁻¹ of 2,4-D or 2.24 kg ka⁻¹ of triclopyr. These herbicide rates were 2 times the recommended field use rates. The field volatility study was performed by placing cotton and soybean plants onto 15x15 m plots previously treated with 2X rates of dicamba, 2,4-D or triclopyr, Plants were exposed to herbicide volatility for 48 h in both the field and greenhouse. All plants were evaluated at l, 5, 9 and 14 DAT using the same injury rating scale used for the rate-response experiments. Field and greenhouse volatility data were then compared to field and greenhouse rate-response curves so that herbicide rates corresponding with observed injury could be calculated for the three herbicides. Using this method, herbicide volatility rates estimated from greenhouse cotton at 14 DAT were 2.7x10⁻³, 9.5x10⁻⁴ and 4.9x10⁻² times the normal rates of 2 4-D dicamba and triclopyr, respectively. Greenhouse soybean at 14 DAT indicated volatility rates of 1.8x10⁻², 7.9x10⁻⁴ and 2.5x10⁻² times the normal rates of 2,4-D dicamba and triclopyr. In addition, field volatility estimations made from cotton injury at 14 DAT were 4x10⁻³, 2x10⁻³ and 1.25x10⁻¹ times the recommended rates of 2,4-D dicamba and triclopyr, respectively. Estimations from field soybean at 14 DAT were 1.6x10⁻¹, 1.0x10⁻² and 1.1x10⁻¹ for 2,4-D dicamba and triclopyr.
Issued also on microfiche from Lange Micrographics.
Includes bibliographical references (leaves 79-80).