Evaluation of WideStrike Cotton Response to Repeated Applications of Glufosinate at Various Application Timings

Glyphosate-resistant (GR) weeds are most challenging for growers to control in cotton in the midsouth region of the United States. As a result, growers in these states are transitioning from a glyphosate-based system to a glufosinate-based system. A field study was conducted in 2010 and 2011 in Georgia, North Carolina, and Tennessee to determine the effect of repeated glufosinate applications to WideStrike cotton applied at various application timings. One to three glufosinate applications at 594 g ai ha(-1) were applied to cotton at the two-leaf, seven-leaf, bloom, or 2 wk after bloom stages. Visual estimates of crop injury were evaluated after each application, in addition to crop height, development, and yield. Crop injury after each glufosinate application typically ranged from 3 to 11%, with higher injury observed where multiple glufosinate applications were made. Crop height differences were noted after the bloom and 2 wk after bloom applications. Treatments that had one, two, or three glufosinate applications had reduced crop height when compared with the weed-free control. Node above cracked boll ratings also indicated that glufosinate treatments may have stressed the cotton. Ultimately, yield was reduced where three glufosinate treatments were applied to WideStrike cotton. In addition, one glufosinate application at the bloom stage or two glufosinate applications at the bloom and 2 wk after bloom stages reduced yield when compared with the weed-free control. Although it is a legal application, growers should use caution when applying glufosinate to WideStrike cotton because the manufacturer of glufosinate and the manufacturer of WideStrike cotton do not recommend this application. However, where GR Palmer amaranth is present, these applications may be necessary.