Injury Potential from Herbicide Combinations in Enlist® Cotton

Enlist® cotton with tolerance to 2,4-D choline, glyphosate, and glufosinate became publicly available in 2016 to aid growers in controlling glyphosate-resistant weed species. Little data exist regarding the tolerance of Enlist cotton to herbicide tank mixtures containing glyphosate, glufosinate, 2,4-D choline, and S-metolachlor. The objective of this study was to evaluate the tolerance of Enlist cotton to herbicide tank mixtures including these herbicides. Field studies were conducted in 2016 and 2017 where cotton was sprayed with herbicide combinations containing glyphosate, glufosinate, S-metolachlor, 2,4-D choline, and a premix formulation of glyphosate and S-metolachlor. Crop injury consisted of necrosis, chlorosis, visual stunting, injury on new growth, and total injury at 7, 14, and 28 days after application (DAA). Cotton lint yield was recorded at the conclusion of each growing season. The greatest levels of necrosis and total injury at 7 DAA were observed following applications of glufosinate + S-metolachlor, alone or in combination with glyphosate or glyphosate + 2,4-D choline. The least amount of necrosis and total injury at 7 DAA was observed following applications of glyphosate, glufosinate, S-metolachlor, glyphosate + glufosinate, or glyphosate + S-metolachlor, which produced less than 13% injury. Visual injury at 14 DAA ranged from 8 to 16% across herbicides applied. At 28 DAA, no differences in visual injury were reported. Lint yield was unaffected by herbicide application. Although transient visual injury is expected, Enlist cotton withstood herbicide applications with up to four modes of action in tankmixture without suffering yield reduction.