Underseeding Clover in Organic Wheat to Reduce Mycotoxins and Improve Grain Quality

Final Report for ONE11-137

Project Type: Partnership
Funds awarded in 2011: $14,728.00
Projected End Date: 12/31/2012
Region: Northeast
State: Vermont
Project Leader:
Dr. Sid Bosworth
University of Vermont
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Project Information


This partnership project investigated the practice of underseeding clover in winter wheat and its possible implications for affecting concentrations of the mycotoxin deoxynivalenol (DON) caused by the disease Fusarium head blight (FHB) in grain, grain protein, and grain yield, with the underlying goal of reducing farmer’s risks of mycotoxin contamination in organically managed wheat. An on-farm study was conducted in partnership with Tom and Dave Kenyon, who manage an organic grain farm in the Champlain Valley of Vermont. Replicated strip plots were set up in a field of ‘Redeemer’ winter wheat in March 2011. Frost seeded clover treatments included a control of no clover, medium red clover seeded at 12 lbs per acre and Ladino white clover seeded at 10 lbs per acre. Frost seeding was done by Jon Zirkle, a graduate student at the University of Vermont, and David Kenyon as a team. A field day was held on June 21 and included a tour of the wheat-clover plots with time for attendee questions. In late June wheat heads in plots were visually assessed for FHB incidence and severity and harvested for grain and evaluated for grain protein content and DON levels. Weed and clover biomass measured just before harvest assessed underseeding impact on competition with wheat. Results from this study showed that the incidence and severity of Fusarium head blight as well as DON concentrations was not consistently different between clover treatments nor the non-clover control. Grain yield and protein also were not significantly different between treatments. White clover biomass was significantly higher than the red clover biomass and, as a result, weed biomass was significantly lower in white clover treatment as compared to the red clover and control treatments. All treatment means for DON were very low and were below industry thresholds of 1ppm. Results indicate underseeding clover did not help reduce the incidence of FHB nor did it enhance the disease or affect yield at this particular location and year.


Many Vermont farmers have been motivated to consider growing wheat as local demand and price premiums for organic bread flour increases. However, producing consistently high quality grain can be challenging in the Northeast, particularly due to two important barriers, low grain protein and high mycotoxin levels. The primary mycotoxin of concern is deoxynivalenol (DON) produced by the disease Fusarium head blight (FHB), and is considered the greatest barrier to wheat production in the Northeast (Bergstrom and Darby, personal communication). When DON contaminates grain, it can cause poor baking quality and low test weights from shriveled kernels, as well as human illness and livestock weight loss and vomiting (Sutton 1982). Vermont wheat producers who do not meet the DON guidelines (< 1ppm) set by the FDA (1993) for human consumption often sell grain as animal feed and receive nearly half the price offered for organic flour (Tom Kenyon, personal communication), thereby reducing supplies of locally-produced organic flour.

Changing weather patterns such as wetter summers as noted by Vermont farmers may be encouraging outbreaks of diseases such as FHB, which relies in part on rain splash to infect wheat heads shortly after wheat flowering (Jenkinson and Parry 1994, Gilbert and Tekauz 2000). Such weather events may be especially problematic in fields where wheat is grown directly following a grain crop – a practice not uncommon in Vermont – as kernels and crop stubble remaining on the soil surface serve as hosts for fungal pathogens such Fusarium spp which easily infect the new wheat crop (Sutton 1982, Dill-Macky and Jones 2000).

Although weather can have an influence on FHB and DON, cultural practices can also be important in minimizing these risks (Sutton 1982, Dill-Macky and Jones 2000). This project will investigate the practice of underseeding clover in winter wheat and its possible implications for DON concentrations in grain, grain protein content, and grain yield, with the underlying goal of reducing farmer’s risks of mycotoxin contamination in wheat. Any positive associations found between wheat-clover intercropping and desired grain quality may further incentivize Vermont producers to underseed wheat with clover, a practice that offers ecological benefits such as increased soil organic matter and soil nitrogen for subsequent crops, reduced soil erosion and nutrient loss after grain harvest, and habitat for pollinators and beneficial insects (Magdoff and van Es, 2009). If this is the case, underseeding clover may further appeal to producers seeking efficient ways to transition wheat fields to pasture or hay fields, generate winter cover, or reduce field traffic, fuel costs, and emissions.

Many Vermont farmers new to organic wheat production are seeking effective organic strategies for weed suppression, improving soil health, increasing yields, and crop rotation. While focusing on organic wheat disease management, this project also seeks to address these questions raised by producers, many of whom see organic wheat as a viable cash crop and a way to diversify the farm in a rapidly-changing agricultural economy.

Bergstrom, Gary. 2011. Personal communication. Cornell University, Ithaca, NY.
Darby, Heather. 2011. Personal communication. University of Vermont Extension, St Albans, VT.
Dill-Macky, R. and K.K. Jones, 2000. The effect of previous crop residues and tillage on Fusarium head blight of wheat. Plant Dis. 84, 71-76.
Food and Drug Administration. 1993. Washington, D.C.
Gilbert, J., and A. Tekauz, 2000. Recent developments in research on Fusarium head blight of wheat in Canada. Can. J. Plant Pathol. 22, 1-8.
Jenkinson, P., and D.W. Parry, 1994. Splash dispersal of conidia of Fusarium culmorum and Fusarium avenaceum. Mycol. Res. 98, 506-510.
Kenyon, Tom. 2011. Personal communication. Aurora Farms, Charlotte, VT
Magdoff, Fred and Harold van Es, 2009. Building Soils for Better Crops, 3rd ed. Sustainable Agriculture Research and Education program, USDA,
Sutton, J.C., 1982. Epidemiology of wheat head blight and maize ear rot caused by Fusarium graminearum. Can. J. Plant Path. 4, 195-209.

Project Objectives:

Our primary objective was to see if the practice of underseeding clover into wheat, tested at field scale, would help reduce the incidence of Fusarium head blight by providing a barrier for surface splash of Fusarium spp. inoculum and, therefore, reduce the severity of mycotoxin concentrations in the grain. In addition, we also evaluated the impact of underseeded clover on grain yield and protein content.


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  • Jon Zirkle


Materials and methods:

The experiment was designed and implemented in 2011 by Jon Zirkle, UVM graduate student, and on March 27, plots were flagged off into an existing winter wheat field (cultivar ‘Redeemer’) and, with the assistance of cooperating farmer’s Tom and David Kenyon, clover treatments were frost seeded into designated 30 by 100 foot replicated strip plots using a hand broadcast spreader.

In May, soil samples were collected and rain-splash traps were set up in each plot to collect splash samples containing suspended Fusarium spp. propagules to then be cultured in the lab.

In June and July, rain splash samples were collected immediately after three rainfall events (June 10, June 23, June 25). Splash samples were plated onto a selective agar media that only allows fungi in the Fusarium genus to grow, and colonies were quantified to generate density and total propagule loads from the splash collected during the three rain events. Morphological traits of Fusarium spp. isolates were examined under microscope and some were examined further by DNA sequencing at Cornell University to confirm whether isolates belonged to the genus Fusarium.

In July, we examined seven sets of 20 wheat head samples from each plot and assessed Fusarium head blight symptoms for incidence and severity. Quadrat samples of clover and weed biomass were collected from randomly chosen areas from each plot using hand clippers.

The plots were harvested on July 16, using two methods. With the first, yields were determined for each strip plot by calculating the difference in pre and post weight of the Kenyon’s combine using a portable drive-on truck scale. However, due unusually wet weather, the wheat was much shorter than normal and the clover was relatively tall, making it very difficult to efficiently harvest with the combine. As a result, the truck scales were not sensitive enough to provide reliable measurements for the small amount of differences we got between pre and post harvest weights. Therefore, hand samples of a two meter area of wheat were thus gathered and used to calculate yield as a second method. The grain from hand sampling was threshed and cleaned for DON testing and protein analysis.

From August to October time we conducted lab analysis of the grain for crude protein, DON concentrations, Fusarium spp. colony forming units (CFUs) from rain splash samples, and to summarize and analyze data. Preliminary results were shared with the Tom and David Kenyon in October to discuss the outcome.

Research results and discussion:

In this study, we found that the incidence and severity of Fusarium head blight as well as DON mycotoxin concentrations was not consistently different between clover treatments nor the non-clover control (see Table 4). We also found that grain yield and protein were not significantly different between treatments (Table 1). White clover biomass was significantly higher than the red clover biomass and, as a result, weed biomass was significantly lower in white clover treatment as compared to the red clover and control treatments. DON, though not significantly different, was highest in red clover treatments, though all treatment means were well below industry thresholds (1ppm).

Due to unusually heavy rainfall in May and early June of 2011, clover establishment was slow and wheat showed slow growth as well as signs of nitrogen deficiency and foliar disease. However, as summer progressed, clover nearly overtook the wheat, given the inadequate fertility available to the wheat which kept it short. Participating farmer Tom Kenyon had difficulty raising the combine high enough to harvest wheat due to the short wheat height and vigorous clover growth in some areas. As a note, at three winter wheat sites that had similar research studies but on smaller plots that was conducted the previous year (2010), we did not have this problem. Spring rainfall was more typical and growth of the wheat was more typical; therefore, the wheat was clearly taller than the clovers and harvest was not an issue.

Research conclusions:

This project has been able to enhance other on-going research that we have been conducting regarding underseeded clover in wheat and in increasing our knowledge and understanding of how underseeded clover crops interact with wheat growth, diseases and weeds. The Kenyons were very interested in this project from the onset. They had not used this practice of underseeding much before this project. They did end up rigging a ATV mounted spinner and frost seeded red clover into areas of the field outside of our study area. At the recent NGGA conference in March 2012, Sid Bosworth presented the findings of this project and assessed the impact it has had on other grain producers in Vermont and the region.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

• On June 21 we offered an on-farm field day to highlight the project. There were approximately 20 to 25 attendees made up of farmers, agency personnel and college students. We were able to show attendees how well the clover had established, pointing out evidence in the field of Fusarium infection (bleaching), and explain the objectives of the trial. Considerable discussion was centered on the impacts of the heavy rain and visible stunted wheat. We also found and pointed out that ‘Redeemer’ is very susceptible to foliar diseases such as Ascochyta spp. and Septoria spp. infections.
• A presentation on Jon Zirkle’s master thesis research on interseeding clover into winter and spring wheat, including research for this SARE study, was presented at the annual meeting of the American Society of Agronomy in October 2011 in San Antonio, TX. Citation: Zirkle, Jon, Sid Bosworth, Heather Darby. 2011. Organic wheat with clover: impacts on fusarium spp. inoculum dispersal, deoxynivalenol concentration, crude protein, grain yield, and weed biomass. Annual Meetings of the ASA-CSSA-SSSA Abstracts (2011 Madison, WI).
• A presentation on Jon Zirkle’s master thesis research, including research for this SARE study, was presented at his thesis defense Feb. 2, 2012 at the University of Vermont and with approximately 25 attending including students, faculty and farmers (members of the Northern Grain Growers Board).
• Results were presented at the annual Northern Grain Growers Association winter conference, held March 15, 2012 in Essex, VT with 145 attending (with this session attended by 15 to 20 farmers and agricultural service providers).
• A summary article for the spring issue of the Northern Grain Growers Association newsletter is in the process of being written to date.

Project Outcomes

Project outcomes:

This practice is fairly simple and does not require any special equipment that most grain farms don’t already have. In the study area’s strip plots, a chest spreader with hand crank was used for frost seeding. The major costs for this practice include the cost of the clover seed (estimated at $25 to $50 per acre at the rates applied in this study) plus the labor to plant it (estimated at $12 per acre based on local custom costs in the Northeast) for a total of $37 to $62 per acre. Higher cost estimates suggested above are based on one type of certified organic clover seed, though less expensive seed may be feasible to acquire. We did not get a measurable benefit in yield or grain quality from this study. The possible intangible benefits of an underseeding of legume cover crops such as reduced soil erosion, increased soil nitrogen and organic matter, weed seedbank control, and increased nectar and pollen for pollinators are all difficult to measure for placing an economic value. However, in challenging weather years where drought or significant rain events lead to flooding, greater soil protection and more consistent soil moisture levels from clover understory may enable protecting soil resources and ensure future wheat crops are able to be sustained in fields susceptible to erosion.

Farmer Adoption

The Kenyons were very interested in this project from the onset. They had not used this practice of underseeding much before this project. They did end up rigging a ATV mounted spinner and frost seeded red clover into areas of the field outside of our study area. The Kenyons remain interested in frost seeding, and many of the organic wheat producers in Vermont have expressed interest in using white clover for underseeding and have expressed optimism in learning that this practice did not increase disease symptoms. At least one Vermont producer has expressed interest in investigating his own further experimentation with other types of clover underseeding (including mixes) and more closely examining yield and quality effects of using clover in his rotation scheme as a result of this research.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

This study exposed a number of areas for potential further research. The limited temporal data failed to capture wheat-clover performance under a dry year, as precipitation was excessive and sporadic. Expanding research to examine clover underseeding practices on different soil types, better growing years, different clover species and/or cultivars as well as seeding rates could further improve understanding and producer confidence of this practice. Other possible areas of further study could include:
• Examination of foliar disease pathogens of organic wheat such as Ascochyta spp. and Septoria spp. infections and how their dynamics are affected by clover underseeding of organic wheat
• Exploring impacts of various clover underseeding dates on wheat performance and grain quality
• Testing agronomic and disease results when underseeding with other underseeding legumes or other clover species and/or cultivars than those chosen in this pilot study
• Additions of experimental controls that were not in grain or grass crops the previous year (example: in nearby field previously in alfalfa) to further examine localized effects of rotation and availability of Fusarium spp. host residues.
• Investigating recent weather data (last 20 years, etc) of wheat growing season in Vermont/Northern New England to assess probabilities of increased risk of fungal diseases of organic wheat under changing climatic conditions, leading to potential modeling and forecasting of disease likelihood.
• Survey of organic wheat producers in northern New England to assess adoption of this practice, concerns, perceived risks, greatest disease-related barriers to organic production, and greatest underseeding crops of interests that have not yet been researched in the region.
• In-depth survey of Fusarium species found in soils of wheat-clover fields in northern New England or a survey of Fusarium spp. found in harvested grain.

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.