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29 December 2021 Safety and efficacy of linuron with or without an adjuvant or S-metolachlor for POST control of Palmer amaranth (Amaranthus palmeri) in sweetpotato
Levi D. Moore, Katherine M. Jennings, David W. Monks, Ramon G. Leon, David L. Jordan, Michael D. Boyette
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Abstract

Field studies were conducted to evaluate linuron for POST control of Palmer amaranth in sweetpotato to minimize reliance on protoporphyrinogen oxidase (PPO)-inhibiting herbicides. Treatments were arranged in a two by four factorial in which the first factor consisted of two rates of linuron (420 and 700 g ai ha-1), and the second factor consisted of linuron applied alone or in combinations of linuron plus a nonionic surfactant (NIS; 0.5% vol/vol), linuron plus S-metolachlor (800 g ai ha-1), or linuron plus NIS plus S-metolachlor. In addition, S-metolachlor alone and nontreated weedy and weed-free checks were included for comparison. Treatments were applied to ‘Covington’ sweetpotato 8 d after transplanting (DAP). S-metolachlor alone provided poor Palmer amaranth control because emergence had occurred at applications. All treatments that included linuron resulted in at least 98% and 91% Palmer amaranth control 1 and 2 wk after treatment (WAT), respectively. Including NIS with linuron did not increase Palmer amaranth control compared to linuron alone, but it resulted in greater sweetpotato injury and subsequently decreased total sweetpotato yield by 25%. Including S-metolachlor with linuron resulted in the greatest Palmer amaranth control 4 WAT, but increased crop foliar injury to 36% 1 WAT compared to 17% foliar injury from linuron alone. Marketable and total sweetpotato yields were similar between linuron alone and linuron plus S-metolachlor or S-metolachlor plus NIS treatments, though all treatments resulted in at least 39% less total yield than the weed-free check resulting from herbicide injury and/or Palmer amaranth competition. Because of the excellent POST Palmer amaranth control from linuron 1 WAT, a system that includes linuron applied 7 DAP followed by S-metolachlor applied 14 DAP could help to extend residual Palmer amaranth control further into the critical period of weed control while minimizing sweetpotato injury.

Nomenclature: Linuron; S-metolachlor; Palmer amaranth; Amaranthus palmeri S. Wats AMAPA; Ipomoea batatas (L.) Lam. ‘Covington ‘

© The Author(s), 2021. Published by Cambridge University Press on behalf of the Weed Science Society of America.
Levi D. Moore, Katherine M. Jennings, David W. Monks, Ramon G. Leon, David L. Jordan, and Michael D. Boyette "Safety and efficacy of linuron with or without an adjuvant or S-metolachlor for POST control of Palmer amaranth (Amaranthus palmeri) in sweetpotato," Weed Technology 35(3), 471-475, (29 December 2021). https://doi.org/10.1017/wet.2021.27
Received: 18 December 2020; Accepted: 4 April 2021; Published: 29 December 2021
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KEYWORDS
nonionic surfactant
surfactant
tank mix
weed control
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