Influence of Environmental and Physiological Factors on Glufosinate and Glyphosate Weed Management.

Abstract

Field studies were conducted near Clayton, Lewiston, and Rocky Mount, NC in 2005 to evaluate weed control and cotton response to PRE treatments of pendimethalin alone or in a tank mixture with fomesafen, POST treatments of glufosinate applied alone or in a tank mixture with S-metolachlor, and LAYBY treatments of glufosinate in a tank mixture with flumioxazin or prometryn.

Field studies were conducted near Clayton, Goldsboro, Kinston, and Rocky Mount, NC in 2003 to evaluate weed control and cotton response to POST treatments of glufosinate applied alone or in tank mixtures with S-metolachlor, pyrithiobac, or trifloxysulfuron.

Field studies were conducted near Rocky Mount, NC in 2004, Clayton, NC, Lewiston-Woodville, NC, Florence, SC, St. Joseph, LA, and Suffolk, VA in 2005 to evaluate weed control and cotton response to postemergence treatments of glufosinate or glyphosate on glufosinate-resistant and glyphosate-resistant cotton, respectively, applied alone or in tank mixtures with S-metolachlor EPOST.

Greenhouse studies were conducted to evaluate phytotoxicity and corresponding physiological response to simulated rainfall following POST treatments of various formulations of glufosinate or glyphosate on goosegrass, Palmer amaranth, and pitted morningglory. Ammonia levels and shikimic acid levels were used as diagnostic markers for glufosinate and glyphosate, respectively. A rain-free period of 4 hours is needed to adequately control goosegrass and Palmer amaranth, while up to 24 hours is needed to control pitted morningglory with glyphosate. A rain-free period of 1 hour is needed to provide maximum control of goosegrass and pitted morningglory with glufosinate; however a rain-free period of at least 24 hours is needed to achieve maximum control of Palmer amaranth.

Greenhouse studies were conducted to evaluate absorption, translocation, and metabolism of 14C-glufosinate in glufosinate-resistant corn, glufosinate-resistant cotton, non-transgenic cotton, goosegrass, large crabgrass, Palmer amaranth, pitted morningglory, and sicklepod. Absorption of 14C-glufosinate varied by species. Significant levels of translocation were observed in glufosinate-resistant corn and Palmer amaranth. Metabolites of 14C-glufosinate were detected in all crop and weed species.