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Title: COMPARISON OF TOTAL POSTEMERGENCE WEED CONTROL PROGRAMS IN SOYBEAN

Author
item HART, STEPHEN - UNIV OF ILLINOIS
item Wax, Loyd
item HAGER, AARON - UNIV OF ILLINOIS

Submitted to: Journal of Production Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: We are developing weed control systems to emphasize postemergence herbicides and reduce the amount of soil applied herbicides that seem to have greater potential than foliar applied herbicides for contaminating surface and ground water. However, many of the postemergence herbicides in use control weeds by attacking the same system in plants, the ALS (acetolactate synthase) enzyme. Some biotypes of various weeds are becoming resistant to this ALS-inhibitor type of herbicide. Thus, we set up experiments to compare postemergence systems, using ALS and non-ALS herbicides, alone and in combination, to find the best combinations of postemergence herbicides for weed control in soybeans. We conducted this work at two locations in Illinois for two years on various weeds in soybean. In three out of four experiments, combinations of non-ALS herbicides had the potential to provide broad spectrum weed control that was equal to that with the ALS-inhibitor herbicides, when applications were made under favorable environmental conditions and weed growth stages. The results of these studies provide additional options for reducing herbicide total inputs with postemergence weed control without dependence on soil-applied herbicides, but scouting and timely application will need to be used for this to be a successful system. These results should be beneficial to various weed science personnel who are engaged in developing improved weed management systems in soybean.

Technical Abstract: Field studies were conducted in 1994 and 1995 in central and southern Illinois to compare several total postemergence weed control programs in soybean (Glycine max (L.) Merr.). Herbicide programs evaluated were imazethapyr (an ALS inhibiting herbicide) applied alone or in combination with lactofen and two non-ALS herbicide programs consisting of combinations of bentazon, acifluorfen, and sethoxydim and combinations of fomesafen, fluazifop and fenoxyprop. These treatments were applied early postemergence (V1 soybean) and postemergence (V2 soybean). Non-ALS herbicide programs generally provided more effective weed control POST, while weed control with imazethapyr tended to be greater EPOS. Non-ALS herbicide programs applied POST provided weed control levels that were equal to imazethapyr in three out of four experiments. In 1994 at Brownstown, broadleaf weed control was poor with non-ALS herbicide programs when weed growth stages were larger and environmental conditions more extreme as compared to other experiments. Adding lactofen to imazethapyr increased broadleaf weed control in some instances but decreased giant foxtail control. Imazethapyr plus lactofen tended to produce the greatest degree of soybean injury.