ECOLOGICAL BASES FOR WEED MANAGEMENT IN SUSTAINABLE CROPPING SYSTEMS

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0228719
• Multistate No.: NE-1047
• Project Start Date: Oct 1, 2011
• Project End Date: Sep 30, 2015
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF ILLINOIS
2001 S. Lincoln Ave.
URBANA,IL 61801

Performing Department
Crop Sciences

Non Technical Summary
Recent surveys, farmer focus groups, discussions at grower meetings, and individual interactions with farmers indicate that weeds are the most critical management problem facing organic or sustainable farmers who limit their use of herbicides. Weeds reduce crop yields and quality, increase harvest difficulty, and add to the seed bank contributing to future management problems. Our previous research developed cover crop systems, cultivation methods, and natural product herbicides to manage weeds early during the growing season. Sustainable weed management, however, is based on the integration of multiple tactics that attack weed populations throughout the weed life cycle. This requires an understanding of how ecological processes interact with control measures at various life stages. First, cultivation is a major method of weed management in organic and reduced herbicide systems, but little is known about how soil texture, tilth, and moisture affect the efficacy and selectivity of cultivation implements. Substantial gains in weed control are possible through better matching of the type and timing of implement use to soil conditions. Second, some weeds are missed by cultivation, or are resistant to herbicides or emerge through gaps in the crop canopy. Controlling these weeds by rogueing or post-harvest operations can greatly affect seed input to the weed seed bank. Weed seeds sometimes continue to develop on plants that have been cut, pulled, or treated with herbicide, but information is sorely lacking on how the method of termination and the developmental stage at death affect the number of viable seeds that various weed species ultimately produce. We regularly get questions from growers about the potential for seed production on weeds that have been killed but not removed from the field. Third, once weed seeds have entered the seed bank, they may die, produce emerged seedlings, or persist in the soil and germinate in subsequent years. Information is available on how tillage and seed position in the soil affect the relative probabilities of these three outcomes. Much less is known, however, about how organic matter sources like cover crops and compost affect seed survival and seedling emergence. Some types of organic matter inputs may reduce seed persistence by promoting germination in circumstances where emergence is unlikely or by increasing microbial populations that cause seed decay. Reducing the persistence of weed seeds would reduce weed infestations in subsequent crops. Organic farmers in particular are interested in multi-tactic weed management strategies that involve attack on several stages of the weed life cycle. With the growing prevalence of herbicide resistant weeds, conventional growers too are realizing the usefulness of integrating a variety of practices into their weed management programs. The applied research proposed will provide a knowledge base for improving several important management tactics.

Animal Health Component

85%

Research Effort Categories

Basic

15%

Applied

85%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
213	1411	1140	35%
213	1429	1140	35%
216	1411	1140	15%
216	1429	1140	15%

Knowledge Area
216 - Integrated Pest Management Systems; 213 - Weeds Affecting Plants;

Subject Of Investigation
1411 - Beans (fresh, fresh-processed); 1429 - Cucurbits, other;

Field Of Science
1140 - Weed science;

Keywords

weed kill method

weed seed development

weed seed germination

weed seed burial depth

weed seed survival

seed persistence

weed life cycle

Goals / Objectives
Determine how soil conditions affect efficacy and selectivity of cultivation implements for the control of various weed species. Specifically, we hypothesize that (i) efficacy of cultivation decreases as soil moisture increases and (ii) efficacy decreases as soil roughness (cloddiness) increases. In addition, this objective seeks to obtain information on how different implements are affected by soil factors. Determine the reproductive growth stage at which summer annual weeds can be terminated and still produce viable seeds and quantify the effect of method of life-termination on seed production. The goal of this objective is to provide preliminary insight into an area of weed seed management that has been previously under studied. This research will enable us to develop recommendations for farmers on managing late-season weed escapes. Determine the extent to which soil amendments such as green manures affect seed mortality of various weed species. In particular, we hypothesize (i) that seed persistence will be lower in soil with incorporated green manure, (ii) that species which are cued to germinate by the presence of nitrate will have lower persistence when legume cover crops are incorporated than when no cover crop or a small grain cover crop is incorporated, and (iii) that species with shorter seed half-lives in the soil will be more affected by incorporated green manure than species with relatively longer lived seeds.

Project Methods
For the purposes of this study we have chosen to group common weeds based on floral structure. Group A includes broadleaves that form seeds on individual floral stalks. Group B consists of broadleaf weeds that form seeds within capsules or berries. Members of the Asteraceae family form Group C as they develop seeds on compound flower heads. Finally, Group D consists of grassy weeds which have seed heads. Labs will select one weed species from Groups A, B, and D based on naturally occurring populations at research and on-farm sites; Group C weeds will be optional as a fourth weed choice. Weeds with immature seed will be determined visually or by dissection of reproductive structures from multiple locations on the same plant. The same examination of seed will be used to determine when seed is mature for the final collection. The termination methods are: pulling the plant; clipping/chopping; or applying glyphosate. Each plant will be stored separately. Plants sprayed with glyphosate will be covered with a residue bag. In early November seed production will be determined. Group 1 will be immediately tested for viability by a dormancy breaking treatment and then germinating seeds. Seeds that do not germinate will be stained with tetrazolium chloride. Groups 2 and 3 will be returned to the field surface. Group 2 will be tested for viability and group 3 will be tested for germination. Objective 3 Study A: medium term survival of seeds in amended soil. The experiment will be done in small plots in a replicated block design. Amendment rates will be at the high end of rates commonly used by farmers in the local area. A control treatment that receives no amendment, at least one legume cover crop, and at least one small grain cover crop. Seeds of two or more weed species will be buried late in the fall of year 0 while cover crops are growing, but before incorporation. Packets will be buried too deep to allow emergence of any of the species. Each spring, all packets will be removed from the soil. One set will be analyized for surviving seeds. The other packets will be weighed, opened, and the sand and seeds dumped out and mixed with amendments. After the amendment has been added, the sand and seeds will then be returned to a packet and reburied. The same crop or summer cover crop will be grown on all plots during the summer. The seeds will be counted and viability assessed by light pressure. Species that will be investigated include common lambsquarters, smooth pigweed, Powell amaranth, common ragweed, giant foxtail and hairy galinsoga. Study B: Short Term survival of seeds in amended soil. Additional packets of species to be tested during the fall of year 0 will be buried. Packets will be recovered the spring after burial and every three months thereafter.

Progress 10/01/11 to 09/30/15

Outputs
Target Audience:The target audience was farmers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest?The results were disseminated to a total of 100 farmers at the Illinois Specialty Growers, Agritourism, and Organic Farming Conference. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Our objective was to determine the reproductive stage at which weeds can be terminated and still produce viable seed. In 2012 through 2014 the procedures were similar with the exception that in 2012 we used only one termination time, at first flowering. In the other years we used two termination times, either at first flower or ten days after first flower. All termination times received the same treatments. We used six single plant replications of velvetleaf, Canada thistle, and redroot pigweed. At termination, one half of the plants were cut at the base to simulate hand hoeing and the second half treated with a 2% solution of glyphosate with ammonium sulphate. At termination we measured height of both treatments and harvested the plants cut at the base. Immediately after harvesting the cut plants were placed in nylon mesh bags. We allowed the glyphosate-treated plants to remain standing until early September but covered them with nylon mesh bags. After harvesting, plants from both treatments were laid between soybean rows until just before soybean harvest when they were brought into the laboratory and seed separated. In 2012, plants terminated at the first flowering averaged 69 cm. Although redroot pigweed produced approximately 2,000 seed/ plant, Canada thistle produced approximately 300 seed/ plant, and velvetleaf produced approximately 50 seed/ plant, for all three species no seed were viable. In 2013, the plants terminated at first flower averaged 61 cm in height. The plants terminated at ten days after first flower treatment averaged 68 cm in height. Velvetleaf terminated at first flowering did not produce any seed, probably because the flowers were not adequately developed to produce seed. Velvetleaf terminated 10 days after flowering produced greater than 300 seed/ plant. Only in the velvetleaf terminated with glyphosate were 10 viable seed produced but germination was slight possibly due to seed dormancy. Redroot pigweed plants produced upwards of 3,000 seed but none of the seed were viable (probably due to inadequate carbohydrate reserves available to complete seed development). Canada thistle produced the most seed (112 seed/ plant) in the glyphosate termination at flowering, probably because of its ability to mobilize carbohydrate reserves from its perennial root system. Although some seed were viable, few seed germinated. Our conclusion was that seed can develop on weeds after termination of growth either by cutting or glyphosate treatment. In 2014, plants terminated at first flower ranged from 46 cm for Canada thistle to 81 cm for velvetleaf. The plants harvested at 10 days after first flowering ranged in size from 51 cm for Canada thistle to 91 cm for velvetleaf. Results for seed production, viability, and germination were similar to 2013. Velvetleaf produced no seed when terminated at first flowering while when terminated 10 days after flowering it produced approximately 200 seed/ plant. Redroot pigweed produced approximately 1,700 seed/ plant in the glyphosate treatment at flowering while it produced upwards of 800 seed/ plant in the cut treatment 10 days after flowering. None of the velvetleaf or redroot pigweed seed were viable. Canada thistle in the glyphosate treatment at first flower produced less than 70 seed/ plant, approximately 40 percent of seed were viable and 2 seed germinated. The study was not conducted in 2015 due to the resignation of the Principal Investigator. The message to farmers is that they need to control redroot pigweed, Canada thistle, and velvetleaf before emergence or when small and that rescue treatments should be done before the plants start flowering.

Publications

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: The target audiences were scientists and farmers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? The results were disseminated to 30 farmers at the Illinois Specialty Growers, Agritourism, and Organic Conference. What do you plan to do during the next reporting period to accomplish the goals? The current seed separation will be completed and the experiment repeated.

Impacts
What was accomplished under these goals? Our objective is to determine the reproductive stage at which weeds can be terminated and still produce viable seed. In December 2013 seed counts, viability and germination were determined. Velvetleaf terminated at first flowering did not produce any seed, probably because the flowers were not adequately developed to produce seed. Velvetleaf terminated 10 days after flowering produced greater than 300 seed/plant. Only in the velvetleaf terminated with glyphosate were viable seed produced but germination was slight possibly due to seed dormancy. Redroot pigweed plants produced upwards of 3,000 seed but none of the seed were viable. Probably due to inadequate carbohydrate reserves available to complete seed development. Canada thistle produced the most seed in the glyphosate termination at flowering, probably because of its ability to mobilize carbohydrate reserves from its perennial root system. Although some seed were viable, few seed germinated. Our conclusion was seed can develop on weeds after termination of growth either by chopping or glyphosate treatment. The message to farmers is that they need to control redroot pigweed, Canada thistle, and velvetleaf before emergence or when small and that rescue treatment should be done before the plants start flowering. This spring we established the experiment again. The termination times were at first flowering or ten days after first flowering. One half of the plants were cut at the base to simulate hand hoeing and the other half of the plants treated with a 2% solution of glyphosate with ammonium sulphate. At termination we measured height of the plants and harvested the plants cut at the base. Immediately after harvesting the cut plants were placed in nylon mesh bags. We let the glyphosate- treated plants remain standing until late September but covered them with nylon mesh bags tied at the base to retain any seed. After harvesting the plants were placed between soybean rows until late November when they were brought in. The plants terminated at first flower range from 46 cm for Canada thistle to 81 cm for velvetleaf. The plants harvested at 10 days after first flowering ranged in size from 51 cm for Canada thistle to 91 cm. Seed separation has just begun for this year’s samples.

Publications

Progress 01/01/13 to 09/30/13

Outputs
Target Audience: Other scientists Changes/Problems: A second treatment, plants terminated at ten days after flowering,was added to the research. This was added because of lack of viable seed produced at first flowering. What opportunities for training and professional development has the project provided? Nothing Reported How have the results been disseminated to communities of interest? Nothing Reported What do you plan to do during the next reporting period to accomplish the goals? The current seed separation will be completed and germination tests conducted. Also, the research will be repeated during the next reporting period.

Impacts
What was accomplished under these goals? Our objective is to determine the reproductive stage at which weeds can be terminated and still produce viable seed. In December 2012, germination tests were completed and no seeds germinated supporting the conclusion that the plants failed to produce viable seed when terminated at the first flower stage. This spring, we used two termination times, either at first flower or ten days after first flower. Both termination times received the same treatments. Six single plant replications of velvetleaf, Canada thistle, and redroot pigweed were allowed to grow until they reached either the first flower stage or ten days after flowering stage and treatments applied. One half of the plants were cut at the base to simulate hand hoeing and the second half treated with a 2% solution of glyphosate with ammonium sulphate. At termination we measured height of both treatments and harvested the plants cut at the base. Immediately after harvesting the cut plants were placed in nylon mesh bags. We allowed the glyphosate-treated plants to remain standing until early September but covered them with nylon mesh bags. After harvesting, plants from both treatments were laid between soybean rows until mid-November just before soybean harvest when they were brought into the laboratory and seed separated. The plants terminated at first flower treatments were approximately 29 inches in height before harvesting (cut plants) or treated with glyphosate. The plants terminated at ten days after first flower treatments were approximately 31 inches in height. Seed recovery is ongoing but at this stage the plants terminated at flowering do not have any seed while the plants terminated at ten days after flowering produced substantial seed.

Publications

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: This was the first year of the project and as of yet we have no outputs to report. PARTICIPANTS: Karen Renner, Michigan State; Chuck Mohler, Cornell University; Eric Gallandt, University of Maine; and Mark VanGessel, University of Delaware. TARGET AUDIENCES: The target audience is fellow scientists. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Our objective is to determine the reproductive stage at which annual weeds can be terminated and still produce viable seed. Six single plant replications of velvetleaf, Canada thistle, and redroot pigweed were allowed to grow until they reached the first flower stage and treatments applied. One half of the plants were cut at the base to simulate hand hoeing and the second half treated with a 2% solution of glyphosate with ammonium sulphate. At first flowering we measured height of both treatments and harvested the plants cut at the base. Immediately after harvesting the cut plants were placed in nylon mesh bags. We allowed the glyphosate-treated plants to remain standing until early September but covered them with nylon mesh bags. After harvesting, plants from both treatments were layed between soybean rows until early November when they were brought into the laboratory and seed separated. Both treatments were approximately 27 inches in height before harvesting (cut plants) or treated with glyphosate. No treatment had more than 10 seeds when removed from the field. Germination tests are ongoing but at this stage no seed have germinated. Our conclsion at this stage is that the plants failed to produce viable seed when treated at the first flower stage.

Publications

• No publications reported this period