Palmer Amaranth (Amaranthus palmeri) Management in GlyTol^®LibertyLink^®Cotton

Abstract

Field trials were conducted in Lubbock, TX in 2010 and 2011 to evaluate tank-mix combinations of glyphosate and glufosinate in GlyTol®LibertyLink®cotton for control of Palmer amaranth. Herbicide treatments included glyphosate and glufosinate applied at various tank-mix rate combinations (1X:1X, 1X:0.75X, 1X:0.5X, 1X:0.25X and 1X:0X of glyphosate plus glufosinate), proportional tank-mix rate combinations (1X:0X, 0.75X:0.25X, 0.5X:0.5X, 0.25X:0.75X, and 0X:1X of glyphosate plus glufosinate, where X is 0.84 kg ae ha−1of glyphosate or 0.58 kg ai ha−1of glufosinate ammonium), and in sequential (1X followed by 1X) applications of both herbicides in an overall weed management system. Greenhouse studies were conducted to quantify antagonistic or synergistic effects. Treatments included a nontreated control; glyphosate at 0.84, 0.63, 0.42, and 0.21 kg ha−1; glufosinate at 0.58, 0.44, 0.29, and 0.15 kg ha−1; and all tank-mix combinations of each herbicide rate. Dry weights were converted to percent growth values for each rate of the two herbicides alone, and these values were used to calculate expected responses of tank-mix combinations with the use of Colby's method. Expected values were compared to observed percent growth values using an augmented mixed-model method. Results of field studies indicated that tank mixes of glyphosate and glufosinate were less effective at controlling Palmer amaranth than glyphosate applied alone. The addition of any rate of glufosinate to a 1X rate of glyphosate reduced Palmer amaranth control compared to glyphosate alone. Greenhouse studies confirmed antagonism seen in the field. These results indicate that sequential applications of these two herbicides are a better option for Palmer amaranth weed management.

Glyphosate-Induced Antagonism in Rapid Response Giant Ragweed (Ambrosia trifida)

“…), and velvetleaf (Abutilon theophrasti Medik.) (Bethke et al 2013;Reed et al 2014). Combinations of glyphosate mixtures with fomesafen or sulfentrazone were antagonistic on a number of broadleaved weeds, a result that is attributable to the rapid activity of the latter herbicides minimizing glyphosate transport (Starke and Oliver 1998;Wehtje et al 2008).…”

Late-season surveys to document seed rain potential of Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus) in Texas cotton

“…Amaranthus palmeri and A. tuberculatus are two major weed species infesting cotton-(Gossypium hirsutum L.) production fields in Texas [7][8][9]. These two species are highly competitive with cotton and can cause significant yield losses.…”

Using Glufosinate in Sequential Application Systems with Dicamba on Palmer Amaranth

“…Glufosinate fb dicamba was not as effective as dicamba fb glufosinate 7 and 14 DASA in 2018 and 7 and 21 DASA in 2019. Reed [11] reported minimal control of Palmer amaranth of similar size with two or three sequential applications of glufosinate. In contrast, Corbett et al [17] reported 100% control of 2 to 5 cm and 8 to 10 cm Palmer amaranth following sequential applications of glufosinate made 10 days apart at lower rates of glufosinate per hectare.…”

“…Reed [11] reported applications of glufosinate alone controlled 5 to 10 cm Palmer amaranth greater than 15 to 20 cm Palmer amaranth 14 and 21 days after treatment. Whitaker et al [19] reported that although a second application of glufosinate initially improved Palmer amaranth control, many weeds survived and grew to heights too large to be controlled by a layby application when Palmer amaranth size at initial application was 5 to 8 cm.…”

“…Although glufosinate has the potential to fortify dicamba systems, further research is needed to identify best use practices when using glufosinate and dicamba in sequential applications. Dicamba and glufosinate both offer the most control when Palmer amaranth is less than 10 cm [11,12]. However, timely applications are not always possible and Palmer amaranth has the ability to grow 2 cm per day in favorable conditions [13].…”