Imidazolinone resistance in several Amaranthus hybridus populations

• Published in: Weed science Vol. 48; no. 4; pp. 508 - 513
• Main Authors: Poston, Daniel H., Wilson, Henry P., Hines, Thomas E.
• Format: Journal Article
• Language: English
• Published: Weed Science Society of America 01-07-2000
• Subjects: Acetolactate synthase; ALS; Amaranth; Amaranthus hybridus; Censuses; chlorimuron; Cross resistance; Depopulation; flumetsulam; greenhouses; Herbicide resistance; Herbicide resistant weeds; Herbicides; imazethapyr; negative cross-resistance; Plants; Population growth; Population growth rate; pyrithiobac; thifensulfuron; WEED MANAGEMENT; weed science; Maryland; Virginia
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1614/0043-1745%282000%29048%5B0508%3AIRISAH%5D2.0.CO%3B2

Field and greenhouse studies were conducted to evaluate the responses of several imidazolinone (IMI)-resistant Amaranthus hybridus populations to various acetolactate synthase (EC 4.1.3.18)-inhibiting herbicides. In 1996 field studies, IMI resistance was confirmed in one A. hybridus population (R4) that was not cross-resistant to the sulfonylurea herbicides CGA-277476, chlorimuron, or thifensulfuron. Amaranthus hybridus control with triazolopyrimidine herbicides was ≤ 35%, but control with cloransulam-methyl or flumetsulam plus cloransulam-methyl was higher than with IMI herbicides. Follow-up greenhouse studies were conducted in 1997 and 1998 to investigate the response of one IMI-susceptible (S) A. hybridus population collected near Painter, VA, and four IMI-resistant A. hybridus populations (R1, R2, R3, R4) collected from fields in Somerset County, MD, to postemergence imazethapyr, chlorimuron, thifensulfuron, pyrithiobac, and cloransulam-methyl applications. Resistance to imazethapyr was confirmed in all R populations, and no practical level of cross-resistance to chlorimuron, thifensulfuron, pyrithiobac, or cloransulam-methyl was detected. Based on resistance ratios, R populations were slightly more tolerant to chlorimuron and slightly more sensitive to pyrithiobac, thifensulfuron, and cloransulam-methyl than the S population. Nomenclature: CGA-277476, 2-[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid,3-oxetanyl-ester; chlorimuron; cloransulam-methyl, flumetsulam, imazethapyr, pyrithiobac, thifensulfuron; Amaranthus hybridus L. AMACH, smooth pigweed.