Imidazolinone and sulfonylurea resistance in a biotype of common waterhemp (Amaranthus rudis)

Sarah Taylor Lovell, Loyd M. Wax, Michael J. Horak, Dallas E. Peterson

Research output: Contribution to journalArticlepeer-review


The incidence of weed resistance to acetolactate synthase (ALS) inhibiting herbicides has increased in the United States. In 1993, a population of ALS-resistant common waterhemp was discovered after two confirmed applications of an imidazolinone herbicide. Following another imazethapyr application in the glasshouse, the resistant biotype demonstrated 130-fold resistance to imazethapyr at the whole plant level. The concentration of imazethapyr required to inhibit the ALS activity by 50% was 520 times greater for the resistant biotype than the susceptible. Plants also demonstrated cross-resistance to the sulfonylureas, chlorimuron and thifensulfuron, at the whole plant and enzyme levels. This particular discovery is of concern due to the low number of applications of the selection agent (imazaquin 1989, imazethapyr 1992, and imazethapyr in the greenhouse) and the high degree of cross-resistance eliminating several options for weed control.

Original languageEnglish (US)
Pages (from-to)789-794
Number of pages6
JournalWeed Science
Issue number4
StatePublished - Oct 1 1996


  • Herbicide resistance
  • acetolactate synthase
  • cross-resistance

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Plant Science


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