Weed science: Cotton (Gossypium hirsutum L.) Injury, Growth, and Yield Following Low-Dose Flumioxazin Postemergence Applications

© 2019 The Cotton Foundation 2019. All rights reserved. The effects of postemergence (POST) herbicides off-target movement on cotton has been evaluated, but no data is available evaluating simulated off-target movement of residual herbicides. Therefore, low-dose POST applications of flumioxazin were evaluated in cotton at the cotyledon, two- and four-leaf growth stages. Rates evaluated were 12.5, 25, and 50% of the labeled use rate of 72 g ai ha-1. Necrosis, cotton height and width reduction was observed. Cotyledon cotton was injured 69 to 86%, 80 to 91%, and 84 to 97% following the 12.5, 25, and 50% flumioxazin rates, respectively, 3 through 42 DAT. Injury of two-leaf cotton increased from 3 to 14 DAT for all flumioxazin rates with maximum injury of 40, 47, and 58% following the 12.5, 25, and 50% rates, respectively, 14 DAT, but injury decreased following the 14 DAT evaluation. Injury of four-leaf cotton was 46 to 58% 3 DAT and decreased over time regardless of rate. At 42 DAT, two- and four-leaf cotton was injured 14 to 33% and increased with flumioxazin rate. Cotton height and width averaged 40, 80, 86% of the nontreated following the cotyledon, two-, and four-leaf application timings, respectively, 42 DAT. In addition, height was more influenced by flumioxazin rate than cotton width. Yields were 24, 52, and 62% of the nontreated following the cotyledon, two-, and four-leaf applications timings, respectively. In addition, yields following the 12.5, 25, and 50% rates were 53, 45, and 40% of the nontreated. Low-doses of flumioxazin reduced revenue $1,172 to $2,344 ha-1 for lint and $212 to 423 ha-1 for cotton seed. Low-doses of flumioxazin POST can have negative effects on cotton growth and yield and could cause severe economic loss for a cotton producer