Published online by Cambridge University Press: 20 January 2017
New arylpicolinate herbicide chemistry under development for rice, aquaticweed management, and other uses was evaluated using five aquatic plants. Theherbicide4-amino-3-chloro-6-(4-chloro-2-fluoro-3-methoxyphenyl)-5-fluoro-pyridine-2-benzylester—also identified as XDE-848 BE or SX-1552 (proposed InternationalOrganization for Standardization common name in review; active tradename RinskorTM)—and its acid form (XDE-848 acid or SX-1552A) wereevaluated on three dicots: (1) Eurasian watermilfoil (EWM), (2) megalodonta,and (3) crested floating heart (CFH), and two monocots: (1) hydrilla and (2)elodea. A small-scale Organization for Economic Cooperation and Development(OECD) protocol developed using EWM for registration studies was utilized.EWM and megalodonta were also evaluated in larger-scale mesocosms forcomparison. In-water concentrations between 0.01 and 243 μg ai L−1 as SX-1552 or SX-1552A were applied under staticconditions for 14 (growth chamber) or 28 d (mesocosm). EWM was susceptibleto both SX-1552 and SX-1552A, with dry-weight 50% effective concentration (EC50) values of 0.11 and 0.23 μg ai L−1 undergrowth chamber conditions. Megalodonta had EC50 values of 11.3and 14.5 μg ai L−1 for the SX-1552 and SX-1552A. CFH was moresensitive to SX-1552 (EC50 = 5.6 μg ai L−1) than toSX-1552A (EC50 = 23.9 μg ai L−1). Hydrilla had EC50 values of 1.4 and 2.5 μg ai L−1, whereaselodea was more tolerant, with EC50 values of 6.9 and 13.1 μg ai L−1 for SX-1552 and SX-1552A, respectively. For EWM mesocosmtrials, EC50 values for SX-1552 and 1552A were 0.12 μg ai L−1 and 0.58 μg ai L−1, whereas the megalodonta EC50 was 6.1 μg ai L−1. Activity of SX-1552 on EWM,hydrilla, and CFH merits continued investigation for selective aquatic weedcontrol properties. Results suggest that the OECD protocol can be used toscreen activity of herbicides for multiple aquatic plant species.
Associate Editor for this paper: Steven Seefeldt, University of Alaska at Fairbanks.