Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/20/2003
Publication Date: 10/30/2003
Citation: Chachalis, D., Reddy, K.N. 2003. Pelargonic acid and rainfall effects on toxicity, absorption, and translocation of glyphosate in trumpetcreeper (campsis radicans). Weed Technology. 18:66-72. Interpretive Summary: Trumpetcreeper is a native perennial vine found extensively in crop and noncrop lands in the Mississippi Delta region. It is difficult to control because of an extensive deep root system. Glyphosate, a non-selective herbicide has potential to control trumpetcreeper, but in-depth studies are lacking. Scientists at the Southern Weed Science Research Unit conducted studies to determine synergistic effects of pelargonic acid (a natural product) on glyphosate activity, absorption, and translocation in trumpetcreeper. We determined that effective control of trumpetcreeper required glyphosate rates higher than 2.24 kg/ha and adding pelargonic acid did not improve activity. A 2.5 cm rainfall within 24 hours after herbicide application resulted in loss of one-fifth activity of glyphosate. Absorption studies indicated that although absorption is rapid with considerable amounts absorbed, these amounts were not sufficient to provide rainfastness up to 48 hours after herbicide application in trumpetcreeper. Addition of pelargonic acid to glyphosate did not increase translocation of glyphosate to rootstocks which is essential for effective control of trumpetcreeper.
Technical Abstract: The effects of pelargonic acid and rainfall on glyphosate activity, absorption, and translocation in trumpetcreeper were investigated. Four- to six-leaf stage (18 to 24 cm tall) trumpetcreeper plants raised from rootstocks were treated with glyphosate at 0, 0.56, 1.12, 2.24, and 4.48 kg ai/ha. Glyphosate at rates 2.24 kg/ha and higher controlled >98% trumpetcreeper and completely inhibited regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm water (7.5 cm/h intensity) applied within 24 h after glyphosate application (HAA) reduced efficacy by one-fifth compared with no simulated rainfall. Absorption of 14C-glyphosate in trumpetcreeper increased from 2.3% to 20.2%, and translocation from 0.4% to 10.5% from 6 to 192 HAA, respectively. At 192 HAA, 9.7% of the recovered 14C-label remained in the treated leaf, 0.6% moved above the treated leaf, and 9.9% moved below the treated leaf. The addition of pelargonic acid (0.5 to 3%, v/v) to glyphosate did not improve glyphosate activity on trumpetcreeper compared with glyphosate alone. The addition of 3% (v/v) pelargonic acid to glyphosate had no effect on absorption and translocation of 14C-glyphosate compared with glyphosate alone. These results show that longer periods of trumpetcreeper leaf exposure to glyphosate could increase its absorption, translocation to rootstocks, and subsequent control.