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Title: IDENTIFICATION OF A SMOOTH PIGWEED BIOTYPE IN ILLINOIS RESISTANT TO VARIOUSALS-INHIBITING HERBICIDES

Author
item HAGER, AARON - UNIV OF ILLINOIS
item WAX, LOYD
item TRANEL, PATRICK - UNIV OF ILLINOIS

Submitted to: North Central Weed Science Society US Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/14/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The occurrence of herbicide resistant weed biotypes in Illinois has continued to increase over the past several years. Biotypes of common and tall waterhemp demonstrating resistance to various ALS-inhibiting herbicides have been reported as well as biotypes of kochia with resistance to triazine and/or ALS-inhibiting herbicides. Continued reliance on specific herbicides prone to selecting for herbicide resistant biotypes could result in additional weed species becoming more difficult to control. During 1997, a population of smooth pigweed in Edgar county, Illinois was not controlled by a postemergence application of imazethapyr. Greenhouse and field research was initiated to determine if selection of ALS-resistant biotypes had occurred. In greenhouse tests, four rates of imazethapyr, imazamox, thifensulfuron, and halosulfuron, corresponding to 0.1, 1, 10 and 100 times the field use rate, were applied when smooth pigweed seedlings were 10 to 12 cm in height. Visual evaluation 14 days after herbicide application revealed less than 50% control with either imazethapyr or imazamox regardless of herbicide rate, but 70% or greater control with the 1 X use rate of either thifensulfuron or halosulfuron. Field experiments with the resistant smooth pigweed biotype were established during 1998. Field observations corroborated those obtained in the greenhouse. None of the imidazolinone herbicides controlled the smooth pigweed biotype, whereas both sulfonylurea herbicides included in the experiment provided good control. Glyphosate provide 99% control up to three weeks after application.