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Title: IMIDAZOLINONE AND SULFONYLUREA RESISTANCE IN A BIOTYPE OF COMMON WATERHEMP (AMARANTHUS RUDIS)

Author
item LOVELL, SARAH - UNIV OF ILLINOIS
item WAX, LOYD
item HORAK, MICHAEL - KANSAS STATE UNIV
item PETERSEN, DALLAS - KANSAS STATE UNIV

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/22/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: There has been a great increase in recent years in the use of herbicides that kill plants by stopping the activity of a plant enzyme, acetolactate synthase (ALS). In some areas of the West and the Great Plains, some biotypes of weeds have become resistant to some herbicides that inhibit the ALS enzyme. This has usually happened following several repeated applications of the same herbicide. We have discovered a population of waterhemp in the Corn Belt that has become resistant to the herbicide imazethapyr (an ALS inhibitor) and also cross-resistant to several sulfonylurea herbicides that also inhibit the ALS enzyme. This finding is especially important because of only a short history of imazethapyr use before development of the resistant biotype and because of the cross-resistance. This may be of considerable concern since over two-thirds of the herbicides used in soybean production in the Corn Belt kill plants by this method of inhibiting the ALS enzyme, so that there is potential for widespread development of resistance. These results should be useful to public and private sector researchers and extension personnel who are developing weed management systems for corn and soybean production.

Technical Abstract: With the increasing use of ALS inhibiting herbicides, biotypes of resistant weeds are becoming more common. The majority of cases involve sulfonylurea herbicides used consecutively in a continuous crop such as wheat. Recently, several biotypes of resistant common cocklebur were selected with an imidazolinone herbicide. In 1993, a population of acetolactate synthase (ALS) resistant common waterhemp was discovered after two consecutive applications of imazethapyr. On the whole plant level, the resistant biotype demonstrated 130-fold resistance to imazethapyr. 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 great concern due to the low number of applications of the selection agent and the high degree of cross-resistance.