Characterization of multiple herbicide–resistant waterhemp (Amaranthus tuberculatus) populations from Illinois to VLCFA-inhibiting herbicides. Issue 4 (July 2019)

• Record Type: Journal Article
• Authors: Strom, Seth A.; Gonzini, Lisa C.; Mitsdarfer, Charlie; Davis, Adam S.; Riechers, Dean E.; Hager, Aaron G.
• Is Part Of: Weed science. Volume 67:Issue 4(2019)
• Page Start: 369
• Page End: 379
• Publication Date: 2019-07
• Subjects: Muthukumar Bagavathiannnan, Texas A&M University; Amaranthus tuberculatus management, -- chloroacetamide, -- dose–response study, -- soil-applied residual; 632.505
• DOI: 10.1017/wsc.2019.13
• Languages: English
• ISSNs: 0043-1745

Abstract

Abstract: Field experiments were conducted in 2016 and 2017 in Champaign County, IL, to study a waterhemp [ Amaranthus tuberculatus (Moq.) J. D. Sauer] population (CHR) resistant to 2, 4-D and 4-hydroxyphenylpyruvate dioxygenase (HPPD)-, photosystem II–, acetolactate synthase (ALS)-, and protoporphyrinogen oxidase–inhibiting herbicides. Two field experiments were designed to investigate the efficacy of very-long-chain fatty-acid (VLCFA)-inhibiting herbicides, including a comparison of active ingredients at labeled use rates and a rate titration experiment. Amaranthus tuberculatus density and control were evaluated at 28 and 42 d after treatment (DAT). Nonencapsulated acetochlor, alachlor, and pyroxasulfone provided the greatest PRE control of CHR (56% to 75%) at 28 DAT, while metolachlor, S -metolachlor, dimethenamid- P, and encapsulated acetochlor provided less than 27% control. In the rate titration study, nonencapsulated acetochlor controlled CHR more than equivalent field use rates of S -metolachlor. Subsequent dose–response experiments with acetochlor, S -metolachlor, dimethenamid- P, and pyroxasulfone in the greenhouse included three multiple herbicide–resistant (MHR) A. tuberculatus populations: CHR-M6 (progeny generated from CHR), MCR-NH40 (progeny generated from Mclean County, IL), and ACR (Adams County, IL), in comparison with a sensitive population (WUS). Both CHR-M6 and MCR-NH40 are MHR to atrazine and HPPD, and ALS inhibitors and demonstrated higher survival rates (LD50 ) to S -metolachlor, acetochlor, dimethenamid- P, or pyroxasulfone than ACR (atrazine resistant but HPPD-inhibitor sensitive) and WUS. Based on biomass reduction (GR50 ), resistant to sensitive (R:S) ratios between CHR-M6 and WUS were 7.5, 6.1, 5.5, and 2.9 for S -metolachlor, acetochlor, dimethenamid- P, and pyroxasulfone, respectively. Values were greater for MCR-NH40 than CHR-M6, and ACR was the most sensitive to all VLCFA inhibitors tested. Complete control of all populations was achieved at or below a field use rate of acetochlor. In summary, field studies demonstrated CHR is not controlled by several VLCFA-inhibiting herbicides. Greenhouse dose–response experiments corroborated field results and generated R:S ratios (LD50 ) ranging from 4.5 to 64 for CHR-M6 and MCR-NH40 among the four VLCFA-inhibiting herbicides evaluated.