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Title: COMMON COCKLEBUR (XANTHIUM STRUMARIUM) RESISTANCE TO SELECTED ALS-INHIBITING HERBICIDES

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

Submitted to: Weed Technology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/1996
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. Weeds that are resistant to ALS-inhibiting herbicides are proliferating across portions of the corn belt. We studied 5 'biotypes' of common cocklebur suspected to be resistant because they came from fields treated several years with ALS-inhibiting herbicides. All 5 of these biotypes could not be killed with applications of imazethapyr that were 200 times the normal use rate. Four of the biotypes resisted high application rates of imazaquin. Two the biotypes were resistant to chlorimuron and the unregistered herbicide NAF-75. We established that the resistance in all cases was due to the resistant plant's altered ALS enzyme that was not inhibited by the herbicide. 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: Five biotypes of common cocklebur from fields treated with acetolactate synthase (ALS)-inhibiting herbicides were tested in greenhouse and laboratory studies to determine the magnitude of resistance and cross-resistance to four ALS-inhibiting herbicides. On the whole plant level, all five ALS-resistant biotypes of common cocklebur demonstrated >200-fold resistance to the imidazolinone, imazethapyr. However, only four of the five biotypes demonstrated resistance to another imidazolinone, imazaquin. Additionally, only two of these five biotypes were cross-resistant to the sulfonylurea, and the new triazolopyrimidine sulfonanilide, NAF-75. Resistance and cross-resistance patterns confirmed at the whole plant level were also demonstrated at the enzyme level.