One year's seeding: a seedbank approach to sustainable weed management

Final Report for LNC04-251

Project Type: Research and Education
Funds awarded in 2004: $149,903.00
Projected End Date: 12/31/2008
Region: North Central
State: Michigan
Project Coordinator:
Karen Renner
Michigan State University
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Project Information


To fulfill the lack of information available on sustainable weed management the extension bulletin “Integrated Weed Management ‘One Year’s Seeding…’” (IWM) was released in February 2005 as the result of a collaborative effort of researchers, extension educators, and producers. Since then, over 2,000 copies have been sold, several workshops have been held to present the information to North Central Region farmers, and fifteen on-farm trials have been conducted to test some of the weed management methods published. Thus far, information we have collected from growers indicates that these activities have increased their knowledge of the diversity of weed management techniques.



An exclusive focus on killing seedlings is a major obstacle to sustainable weed management in the North Central Region (NCR), and is reflected in adoption rates of Roundup Ready™ crops as high as 80% in the NCR (Owen and Zelaya, 2002). Dependence on herbicide-resistant crops threatens sustainability through weed species shifts, herbicide resistance, loss of weed management knowledge, chemical dependence, technology fees, and restricted grain markets. Over-use of physical control of weed seedlings in alternative farming systems drives up fuel consumption, destroys soil tilth, and neglects the weed seedbank, which controls long-term weed management success (Liebman and Davis, 2000).

Models of cropping system effects on annual weed populations (Jordan et al., 1995; Davis et al., 2003) show that reducing weed seed numbers in the soil, especially through decreased seed survival, is the key to keeping weed populations small and manageable. For example, underseeding small grains with forage legumes can increase insect consumption of weed seeds and reduce weed populations, compared to sole crops of small grains (Davis et al., 2003). To help farmers implement a seedbank approach to weed management, decision aids are needed.

Michigan State University has made a commitment to providing high-quality, user-friendly agroecology information to producers in Michigan and throughout the North Central Region (Cavigelli et al., 1998; Cavigelli et al., 2000). Through an EPA Pesticide Environmental Stewardship Program grant (June 2003), our team assembled a diverse working group (the Ecological Seedbank Management Working Group) to produce a draft of an easy to use weed seedbank management guide and train MI farmers in its use. In this project we proposed to 1) create a finished version of the manual for publication, 2) train farmers throughout the NCR to use the manual, 3) field test the manual throughout the NCR, and 4) conduct and evaluate on-farm trials to explore new seedbank management methods.

The rationale for this project is that producers looking for alternatives to conventional production practices tend to look to other producers as their first source of information (Walz, 1998), yet this information is not always shared widely, nor does it affect the research agendas of most land-grant weed scientists. We aimed to make public the decision making process of outstanding producers who are already trying to manage the whole weed life cycle, and then extend this information to other producers and to researchers. In doing so, we increased adoption of existing ecological weed management practices and identified gaps in existing weed management knowledge to direct future research. A key assumption in this project was that lack of relevant, reliable information was holding back adoption of ecological weed management practices. The high priority placed on non-chemical approaches to weed management by farmers in the 3rd biennial national survey of organic farmers (Walz, 1998) suggests that this assumption was well-founded.

Literature Review

Annual weeds spend most of their lives as seeds in the soil seedbank (Cousens and Mortimer, 1995). Simulation models of management effects on the population dynamics of annual weeds show that management practices that kill seeds when they are in the seedbank, or prevent new seeds from entering the seedbank, will have a much larger proportional effect on weed population growth and size than management practices aimed solely at killing weed seedlings (Jordan et al., 1995; Davis et al., 2003). Most weed control in the U.S. is targeted at killing weed seedlings, either with herbicides or with cultivation. Ninety percent of all corn and soybean acres in the U.S. are treated with herbicides, totaling more than 90.6 million tons of active ingredients applied annually (Pike et al., 1995). The literature is likewise focused on ways of controlling the weed seedling stage. A search of the agricultural database AGRICOLA in October, 2003, returned 19,490 entries for the search term “herbicides”, 704 entries for the search term “cultivation & weeds”, and 284 entries for the search term “weed seed”, and 32 entries for the search term “weed seedbank.”

Techniques for eliminating weed seedlings are more common than those aimed at weed seeds for an obvious reason: seedlings are much easier to find and destroy than seeds are, especially seeds that are already in the soil seedbank. We are not suggesting that weed seedling control be abandoned; after all, it is a very effective way of reducing potential inputs to the weed seedbank. Rather, seedling control should be complemented with methods that target other stages in the weed life cycle (Mohler, 1996), with the overall goal of reducing weed seedbank density. Inevitably, some seedlings are going to escape early-season control efforts and survive to produce seeds. Can farmers reduce the damage done by these weeds? Can this be done without increasing herbicide applications? And if the weed seedbank is reduced, can this aid future weed control efforts? We believe that the answer to each of these questions is “yes.”

Although most research has focused on weed seedling control, there have been significant findings over the years that suggest good opportunities for seedbank management (Renner, 2000; Buhler, 2002; Elstein and Suszkiw, 2003). Crop competition with weeds is one of the strongest factors affecting the number of seeds that each weed produces, and can be manipulated to minimize weed seed inputs to the soil seedbank (Perera and Hartwig, 1980; Jordan, 1993; Mohler, 2001). Pathogenic fungi and bacteria are important causes of seed death in the soil seedbank (Kremer, 1993; Kennedy and Kremer, 1996), yet little is known about the factors controlling pathogenic attack of weed seeds. Stale seedbed techniques are regularly practiced in low-external-input cropping systems in Europe, greatly aiding other weed management practices (Hatcher and Melander, 2003). Weed seed destruction by insects, rodents and birds can be very important in reducing the weed seed rain (Marino et al., 1997; Menalled et al., 2002), and rates of predation may be manipulated by cropping system characteristics (Davis and Liebman, 2003). Mechanical destruction of weed seeds by harvesting equipment, once a common practice, has also been gaining in popularity (Gossen et al., 1998), and is now commercially available for small grain production in Canada. Interest in weed seedbank management does appear to be growing among weed scientists. A recent international conference on weed seedbank biology and management in Reading, UK, was attended by over 40 delegates from 18 countries (Bakker et al., 2003).

A number of projects in the SARE database were particularly relevant to the extension and research activities that we propose to conduct. The project “Controlling cheat and annual ryegrass in small grains using novel crop harvesting technologies” (Peeper, AS96-025) showed that roller or hammer mills added as aftermarket attachments to combine grain harvesters could dramatically reduce survival of cheat grass seed in small grains. Other projects, including “Cover Cropping and Residue Management for Weed Suppression, Soil Fertility and Organic Crop Production” (LS02-132, Baldwin), and “Diversity & Intensity of Cover Crop Systems: Managing Weed Seed Bank & Soil Health” (LNE01-141, Gallandt) have examined the relationship between cropping system diversification with cover crops and weed seedbank dynamics. One recently funded proposal, “Microbial processes underlying the natural weed suppressiveness of soils” (LNC03-225, Hallett) represents an important advance in seedbank management research—mechanistic as well as descriptive studies of seedbank processes.

Our proposal was complementary with the above proposals, but is also unique. The above projects were primarily driven by the research team, with some on-farm sites and extension of results. Our project was based on the premise that farmer involvement in the question asking stage (e.g. LNC97-112, Mutch: “Enhancing farmer adoption of sustainable agriculture practices via farmer-driven research”) is critical to generating knowledge that farmers want to use. Our work synthesized current farmer and researcher insights into seedbank management strategies, presented this information to producers throughout the NCR, obtained feedback from these farmers on areas that need more work, initiated on-farm research to fill some of these knowledge gaps, and lead to the creation of a sequel to the decision guide. By involving farmers at each stage of the process, our intent was to keep the information relevant and useful to them.

Project Objectives:

This project addressed the lack of practical information on sustainable weed management by engaging farmers and land-grant professionals in a continuous improvement process. A decision support manual for ecological weed management (Integrated Weed Management: One year's seeding... E-2931 Michigan State University Extension bulletin) was presented to farmers, farmers were asked to use and evaluate the manual, and it was determined that a sequel to the original decision guide was needed.

In the short-term, over 400 producers and extension agents learned to use a practical manual for sustainable weed seedbank management at workshops in MI, IL, and WI. The manual is helping farmers manage the whole weed life cycle, rather than focus on the seedling stage only.

In the intermediate-term, over 100 producer-evaluators (PEs) in five states will use the manual to help them manage weeds on their farms and record impacts on their operations. The PEs will diversify their approach to weed management as a result of using the manual. Eleven on-farm trials explored management options for reducing weed seedbanks through sustainable practices. Feedback from producer workshops and PE's who used the manual on their own farms, in addition to results of on-farm trials, are currently being included in the sequel bulletin to the Integrated Weed Management Guide.

In the long term, this project is giving farmers practical alternatives to over-reliance on herbicide resistant crops and chemically intensive post emergence weed control. The rapid loss of hard-won farmer knowledge of integrated weed management is being slowed, or even reversed, as farmers are engaging in the process of making practical knowledge available for their neighbors and for future farmers. Stronger partnerships between farmers and university personnel have been and are continuing to be formed, with better correspondence between farmer needs and researcher activities, resulting in a sustainable agriculture that gains its strength from both human relationships and scientific understanding.


Materials and methods:

This project leveraged SARE funds by building upon the work done in our EPA PESP project to create a working group and draft of the weed seedbank manual. The Farmer Seedbank Management Advisory group met during the winter of 2003/2004 to develop the content for the manual. The manual, “One year’s seeding...”, is not a set of prescriptions. Instead it describes the factors that farmers weigh when making weed management decisions at different stages of the production cycle/weed life cycle. Scenarios are included for various NCR field crops with weed species that the advisory group considered to be most important in each crop. The manual also contains supporting technical information and directs users to additional sources of information on specific aspects of ecological weed management.

Our EPA-funded activities will meshed with this SARE project beginning in September of 2004. The overall approach was to take the draft prepared by the working group and to solicit farmer feedback at three levels for improving and revising the manual for publication:
1) response forms at regional workshops,
2) producer-evaluators who are paid to evaluate the manual on their own farms, and
3) on-farm trials to address knowledge gaps identified at the first two levels.

Workshops: In the winter of 2004/2005, four EPA-funded workshops were held around MI. Additional workshops, led by Dr. Davis, were conducted in IA, IN, MN, OH and WI. The purpose of these workshops was to train producers and extension agents in the use of the manual.

Producer evaluation: From workshop participants, over 100 producer evaluators (PE’s) were selected to evaluate the manual, each evaluator was paid $200 for a complete evaluation. These evaluations were originally going to be used to revise the manual; however, with the amount of additional information requested it was determined that a second complementary bulletin was necessary.

On-farm experiments: Eleven grower-designed on-farm trials were conducted to address knowledge gaps identified in the manual. Farmer participants were selected from the working group and from regional volunteers. Seven of the eleven trials took place outside MI. All participants were paid $200/day devoted to the project, for up to 7 days per year. Local university personnel helped growers with data collection.

Field Days: The on-farm trials offered the opportunity for field days for local growers to attend and discuss the pros and cons of the management approaches being tested. Field days were held at a point during the field season when maximum treatment differences were expected, with specific timing depending upon the objectives of a particular experiment.

Research results and discussion:

In 2005, the extension bulletin “Integrated Weed Mangement ‘One Year’s Seeding…’” was published. Between 2005 and 2007 the bulletin’s 2,000 copies sold out, reaching beyond the North Central Region, spanning from Wyoming to Delaware and into three provinces in Canada.

Between late 2004 and early 2006 several workshops were held in Michigan, Illinois, and Wisconsin covering the topics presented in the extension bulletin. Listed below are the meeting locations, dates, and attendance.

Meeting Location, Meeting Dates, and Attendance

Dane and Columbia Co., WI 03.09.06 17
Dunn Co., WI 03.10.06 26
Branch Co., MI 02.21.05 60
Clinton Co., MI 03.03.05 28
Gratiot Co., MI 02.01.05 13
Kalamazoo Co., MI 01.28.05 170
Lapeer Co., MI 03.16.05 35
Monmouth, IL 08.17.05 65
Ottawa Co., MI 03.02.05 5
Sanilac Co., MI 03.03.05 25
Tuscola Co., MI 12.20.04 125
Total Attendance=569

With attendance of 569 people to our workshops we exceeded our original short term goal of reaching 400 farmers and extension agents. Evaluations, filled out at the end of 4 of the workshops in 2005, revealed that overall attendees rated their increase in overall knowledge and understanding of weeds at ~3.7 on a scale of 1 to 5 (1= none, 5= a lot). When asked about the likelihood that the information they learned would change the way they managed weeds the average rating was a ~3.6 on a scale of 1 to 5 (1=none, 5= a lot). Based on this feedback and the verbal communications of the farmers at the other workshops, the meetings are proving effective. Currently, we are holding further meetings to introduce the guide to more farmers in MI, IL, MN, and WI.

To meet our intermediate project goal, we sent out 110 evaluations to producer-evaluators (PEs) who both attended a workshop and purchased the bulletin. Through these extensive, 21 page evaluations we collected information on improvements that could be made to the IWM bulletin to create an improved second edition. Forty-seven of the evaluations were returned.

Comments from growers in regard to the IWM bulletin:
- “Over the years I have acquired several books and pamphlets on weeds and the control of weeds. I have ranked your IWM as one of my BEST. Please continue to expand our knowledge on this subject.” (Dennis Kellogg, Carson City, MI).
- “I learned a lot of things that will help me in my weed control. I feel more confident knowing more about some problem weeds on my farm. I now know when to spray them so that I can control them.” (Paul Swartzendruber, Pigeon, MI)
- “This manual provides a very good start for the complex journey of learning to manage weed populations in a biologically based system.” (John Simmons, North Branch, MI)
- “Has a lot of good points in controlling weeds. It will be useful in the years to come. Already use some of the practices and maybe use some of the other ideas that I have not thought of or known about. ” (Anonymous)
- "I have been an agronomist for almost 20 years and a CCA for over 15. I sincerely appreciate having a reference that is useful to both the experienced and novice. I learned things reading this book, which was an unexpected and wonderful surprise. I am glad that it goes beyond introductory.” (Anonymous)
- “I have seen some good resources on weed control in my 30 plus years of organic farming although nothing compares to the quality of this book. Not only is this a good reference book, it is a book that should be mandatory reading for every organic/sustainable farmer during the winter months when time usually allows for more detailed reading.” (Dave Campbell, Maple Park, IL)

A brief survey of the North Central Weed Science Society listserv, that includes weed extension educators and university faculty, showed that the IWM bulletin has been a valuable resource.

Comments from extension personnel and university faculty:
- "I have used this bulletin quite a bit for extension presentations. The bulletin is extremely helpful.” (Mark VanGessel, University of Delaware)
- "I have used the IWM bulletin for extension talks. I also taught Weed Management in the off-campus graduate program, and required the students to buy it for class.” (George F. Czapar, University of Illinois)
- “What a great resource. I distribute copies to interested ag producers in the county and the bulletin is well received by those who are actually questioning their farming practice. I have referred the bulletin to the University of Wyoming Cooperative Extension where there was great interest.” (John L. (Lars) Baker, Fremont County Weed and Pest, WY)

Overall, the evaluation of the IWM bulletin has shown it is an excellent resource; however, there are still several areas where survey participants thought it could be expanded. Evaluators suggested a ‘Part II’ or ‘Supplement’ to the IWM bulletin, to complement what they currently are using as a reference. In 2007 we obtained funding though the Integrated Organic Program to produce a complementary bulletin. In this sequel titled “Integrated Weed Management: Fine Tuning the Systems” we will address the following areas.

- Complex crop rotations for organic growers
- Cover crops: positive and negative attributes on weed management, cost/benefit analysis, positive and negative attributes of various covers, seeding rates, planting dates, potential options for no-till production, nitrogen availability for crops and weeds, and implementation into various crop rotations
- Manure/compost: effects on weed seed fate, the potential spread of new weeds, weed species shifts, and the potential for increased weed competitiveness
- Flaming for weed control: how and when, cost effectiveness, what weeds are controlled at what stages, best conditions, plastic mulches
- Biological controls with a focus on grazing
- Economic thresholds for individual weeds and weed complexes
- Organic farmer profiles: in-depth look at how various organic growers approach successful weed management
- On-farm trials from across the North Central Region
- Weed profiles: beyond the “Dirty Dozen from the original IWM bulletin

Another intermediate goal of this project was to hold on-farm, grower-designed trials to test some of the weed management strategies mentioned in the bulletin. In 2006 and 2007, we funded eleven successful on-farm trials. Four of these trials were in Michigan, 3 in Illinois, 3 in Iowa, and 1 in WI. Projects titles included:

- Effects of Corn Planting Time on Weeds (Good Hope, IL)
- Intercropping for Weed Control in Corn (Alma, MI)
- Intercropping with Buckwheat and Oat in Corn (North Branch, MI)
- Cover Crops for Canada Thistle Suppression (Maple Park, IL)
- Mulches for Common Purslane Control in Tomato (Urbana, IL)
- Ridge-till vs. Conventional-till in Soybean (Harlan, IA)
- Cultivator Comparisons for Weed Management (Schoolcraft, MI)
- Flaming and Rotary Hoeing in Corn (Creston, IA and Panora, IA)
- Flaming and Rotary Hoeing in Soybean (Alma, MI)
- Non-synthetic Herbicide for Weed Control in Soybean (West Bend, WI)

The results of the 2006 trials from Michigan were presented at the Great Lakes Vegetable and Farm Market Expo in Grand Rapids, MI and a panel of the participating Michigan growers was available for audience questions. The results of all of the 2006 trials were presented at the 2006 North Central Weed Science Society annual meeting in Milwaukee, WI. All flaming trial results were presented at the 2007 North Central Weed Science Society annual meeting in St. Louis, MO. With funds secured from Project GREEEN, the 2007 trial results have been made available at and advertised through the New Agriculture Network. All of the on-farm trials from 2006 and 2007 will be published in “IWM: Fine Tuning the System” in late 2008 and also will be made available on the web through the New Agriculture Network and

The workshops, on-farm trials, and the distribution of the bulletin across the continent continue to help us meet our long term objective of increasing farmer awareness of alternative methods of weed control. We have and are continuing to create bonds between growers and researchers. These bonds have also helped us meet the long term goal of focusing research on farmers needs.

Research conclusions:

The feedback we received from the workshops, IWM bulletin evaluations, on-farm trials, and meeting presentations have indicated an increase in awareness and implementation of sustainable weed control options in the North Central Region. This trend will continue with the publication of “IWM: Fine Tuning the System” in 2008.

Economic Analysis

The increase in knowledge, and thus efficiency, of weed control options in sustainable systems has unquestionably led to a reduction in weed control costs to growers.

Farmer Adoption

This project reached over 2,000 growers, educators, researchers, and university students through the bulletin, on-farm trials, web posted trial results, workshops, and meetings.

We recommend that farmers look beyond the seedling stage to manage weeds on their farms. Specifically targeting the production and establishment of weed seeds through decreased survival to reproduction, increased predation, increased decay, etc. will help control weeds over the long term.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Davis, A., K. Renner, C. Sprague, L. Dyer, and D. Mutch. 2005. "Integrated Weed Management ‘One Year’s Seeding…’". MSUE bulletin E-2931.

Project Outcomes


Areas needing additional study

Research still remains to be done on in many areas of sustainable weed management, including:

- Resistant weed management
- Cultivation based on environmental factors
- No-till organic production and weed management
- Strategies for increasing weed seed decay and fatal germination
- Management of winter annual weeds that act as alternate hosts for pathogens

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.