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Weed emergence research
by Bob Hartzler and Doug Buhler, USDA-ARS
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November 26, 1997 --  One of the current efforts of the weed science group at ISU is to develop tools to predict emergence of important weeds of corn and soybeans.  Although emergence prediction models have been developed previously, most of these were designed for  researchers and thus were not of much value to people managing weeds in the field.  The Leopold Center for Sustainable Agriculture is sponsoring much of this research through the Weed Science Issue Team.  The objective of the Issue Team is to develop tools that can be used by persons involved in making weed management decisions:  farmers, ag-chemical dealers, and independent crop consultants.

We initiated efforts in this area in 1995 with a study involving four weed species:  giant foxtail, woolly cupgrass, velvetleaf, and waterhemp.  This study characterized the unique emergence patterns of these four species and was the impetus for our current efforts.  Preliminary results of this study are presented in an earlier web article.

The current research project has several objectives related to weed emergence, including:
1) Determine initial emergence timing,
2) Determine longevity of emergence,
3) Determine periods of maximum emergence, and
4) Develop user friendly emergence prediction tools.

An extension bulletin (Relative emergence sequence for weeds of corn and soybeans, ISUE Bulletin SA-11) was published during the spring of 1997 and addressed Objective 1.  The emergence sequences presented in this bulletin are based on previous research and expert opinions of weed scientists throughout the Midwest.

We have expanded our research efforts in the past two years to develop the database needed to fulfill the objectives of the Weed Science Issue Team.   In the fall of 1996 an emergence study was initiated that included 26 weed species.   A portion of the results from this study are presented in the following figure.   The black and yellow bars represent the emergence period for eight of the species in this experiment.  The yellow portion of the bar is the period of maximum emergence for the individual species.  The wide range in emergence patterns among weed species is evident in this graph.  Kochia was the earliest emerging weed and completed emergence by the end of May.  Waterhemp didn't initiate emergence until mid-May and the peak emergence occurred in the first week of July.  Morningglory had the longest emergence period, with seedlings emerging from early May until early August.    These differences in emergence characteristics of weed species are one of the reasons why weed management is such a difficult task.

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Sandell, Buhler and Hartzler.  1997.  Ames, IA.

Future efforts of the Weed Management Issue Team include repeating the above experiment in 1998.  In addition, emergence experiments were initiated at four locations across the state (Nashua, Crawfordsville, Lewis, and Sioux Center) during the fall of 1997 that include ten weed species.  We believe that these studies should provide a broad database that will facilitate the development of emergence prediction tools.  These tools will help improve weed management systems by increasing the efficiency of scouting operations and also help determine the optimum timing for various weed control tactics (seedbed preparation, herbicide application, cultivation, etc.).

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
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