Refining Cotton Replanting Recommendations

The decision to replant suboptimal cotton (Gossypium hirsutum L.) stands has become more challenging in recent years because the suggested retail price per bag of replanting seed has increased by more than 25%. Previous studies have justified replanting when ≥ 50% of planted area is occupied by skips ≥ 0.91 m (3 ft). Revision of replanting recommendations was deemed necessary with the introduction of more advanced and accurate plant and skip detection methods. The objective of this study was to update replanting recommendations using unmanned aerial vehicles (UAVs). The study was conducted at three sites in eastern North Carolina during the 2019 and 2020 growing seasons. Each site had an early- and a late-planted trial. Treatment combinations were produced using various ratios of DP 1646 B2XF and DP 493 cotton seed. Simulated replanted plots were planted with 100% DP 1646 B2XF three to four weeks after initial planting. Following emergence, glyphosate and glufosinate were applied to terminate all conventional seedlings and produce random skips. Cotton skips were detected using a Zenmuse X5 RGB sensor mounted on a UAV. Yield was regressed to the percentage of planted area occupied by skips > 0.91 m. In 2019, the replanted treatment did not yield higher than earlier planted treatments but, in 2020, yields were significantly higher in the replanted treatment compared to most earlier planted treatments. The data suggest that a replant should be triggered when 30 to 40% of the planted area is occupied by skips ≥ 0.91 m.