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ARS Home » Research » Publications at this Location » Publication #70880
Title: PALMER AMARANTH (AMARANTHUS PALMERI) AND COMMON WATERHEMP (AMARANTHUS RUDIS) RESISTANCE TO SELECTED ALS-INHIBITING HERBICIDES

Author
item SPRAGUE, CHRISTY - UNIV OF ILLINOIS
item Stoller, Edward
item Wax, Loyd
item HORAK, MICHAEL

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The use of herbicides that kill weeds by inhibiting the plant enzyme acetolaclate synthase (ALS) has increased rapidly in recent years. In some areas in the cornbelt, some pigweeds are no longer controlled with ALS-inhibiting herbicides. In greenhouse and laboratory studies we found that an ALS-resistant biotype of Palmer amaranth could survive almost 3000 times the normal use rate of imazethapyr, as well as extremely high rates of thifensulfuron and chlorimuron. An ALS-resistant biotype of common waterhemp could withstand 130 times the normal use rate of imazethapyr, and could also withstand the excessively high rates of thifensulfuron and chlorimuron. These plants can withstand the exorbitant applications because their ALS enzyme is altered, compared to the ALS in sensitive plants, and is not inhibited by these herbicides. This information will be very useful to all personnel involved in developing and implementing weed management programs such as growers, crop consultants, researchers, industry personnel, and extension specialists.

Technical Abstract: Imazethapyr-resistant biotypes of Palmer amaranth and common waterhemp were subjected to greenhouse and laboratory studies to determine the magnitude of resistance and cross-resistance to three acetolactate synthase (ALS)-inhibiting herbicides. On the whole plant level, the Palmer amaranth biotype and the common waterhemp biotype demonstrated >2,830- and >130-fold resistance to imazethapyr, respectively. Concentrations of imazethapyr required to inhibit ALS activity by 50% were >13,000 and >1,900 times greater for the resistant biotypes of Palmer amaranth and common waterhemp, respectively, compared to the susceptible plants. Both Amaranthus species demonstrated cross-resistance to the sulfonylurea herbicides, at the whole plant and enzyme levels, indicating that a less sensitive ALS enzyme confers the resistance.