Interaction of Glufosinate with 2,4-D, Dicamba, and Tembotrione on Glyphosate-resistant Amaranthus palmeri

Abstract

Aims: Glyphosate-resistant Amaranthus palmeri S. Wats. (Palmer amaranth) is a major threat to crops in the southern USA. Experiments were conducted to evaluate differential tolerance to 2,4-D, dicamba, and tembotrione and interaction with glufosinate for glyphosate-resistant (GR) A. palmeri control. Study Design: The differential tolerance experiment was conducted in a randomized complete block design (RCBD) with a split-plot arrangement of treatments with herbicide as mainplot and A. palmeri population as subplot. The herbicide interaction experiment was conducted in RCBD with factorial arrangement of treatments. Place and Duration of Study: University of Arkansas-Fayetteville, USA. Tolerance experiments were conducted in October–November 2010 and in July–August 2011. Herbicide interaction experiments were conducted in the greenhouse in June–July 2011 and August–September 2011 and in the field in April–August 2012. Methodology: Differential tolerance to alternative herbicides was evaluated using 12 GR-A. palmeri populations. Herbicide treatments were 1.06 kg ae/ha 2,4-D, 0.56 kg ae/ha dicamba, and 0.094 kg ai/ha tembotrione. In the herbicide interaction study, glufosinate at 0.18, 0.36, and 0.73 kg ai/ha were mixed with either 0.024, 0.047, and 0.094 kg ai/ha tembotrione; 0.28, 0.56, and 1.12 kg ae/ha 2,4-D; or 0.28 and 0.56 kg ae/ha dicamba. The population used was PRA-C. Results:  In the tolerance experiment, 2,4-D at 1x (1.06 kg ae/ha) killed 96-100% of plants per population. Dicamba at 1x (0.56 kg ae/ha) killed 36-94% of plants per population, with survivors sustaining 80-99% injury. Tembotrione at 1x (0.094 kg ai/ha) caused 49-98% mortality per population with survivors incurring 80-99% injury. In the herbicide interaction experiment, mixing half doses of glufosinate and 2,4-D resulted in 100% control of PRA-C in the greenhouse and field. At 1x, glufosinate controlled PRA-C 91% in the field; the addition of 0.5x or 1x of 2,4-D or 1x of dicamba resulted in 100% control. Conclusion: In the field, 2,4-D was most effective on GR-A. palmeri, relative to dicamba and tembotrione. Some populations have a high risk of being selected for resistance to dicamba, glufosinate, and tembotrione. Glufosinate + 2,4-D mixtures were additive and at sublethal doses, synergistic. Most combinations of glufosinate and tembotrione were antagonistic