Suppression of Soybean Diseases Through the Use of Cover Crops

Final Report for LNC10-321

Project Type: Research and Education
Funds awarded in 2010: $174,823.00
Projected End Date: 12/31/2013
Region: North Central
State: Illinois
Project Coordinator:
Dr. Darin Eastburn
University of Illinois
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Project Information

Summary:

The impacts of fall cover crops on diseases in spring planted soybeans were conducted at 6 locations in Illinois. Soybean stand establishment was highest in rye plots inoculated with Rhizoctonia solani, as compared to the fallow plots, and Rhizoctonia root severity rot was lowest in the rye plots. Counts of soybean cyst nematodes were reduced in rye and rape plots at several locations. Greenhouse assays of field soils showed reductions of Rhizoctonia root rot and sudden death syndrome in rye and rape soils. No differences in other pathogens or microbial communities were detected among soils from the cover crop treatments.

Introduction:

Context, Background, Rationale, and Need

Diseases of soybean annually cause significant reductions in soybean yields as a result of disruption of root and vascular function, loss of photosynthetic area, and direct degradation of the beans. Important soybean diseases in the Midwestern US include those caused by plant pathogenic fungi, nematodes, bacteria, and viruses. Some seed/seedling diseases are managed through the application of seed protectant fungicides, and foliar fungicides are often applied in southern soybean growing regions of the US to combat foliar diseases such as frogeye leaf spot and more recently Asian soybean rust. Soilborne diseases such as sudden death syndrome (SDS), charcoal rot, Rhizoctonia rot, Sclerotinia rot (white mold), and Phytophthora rot can be particularly problematic, as they are very widespread and difficult to manage.

Most commercial soybean growers in the Midwest rely on only three disease management strategies instead of a toolbox of integrated pest management (IPM) practices. These three limited strategies are crop rotation, disease resistant varieties, and, more recently, seed treatment and foliar fungicides. Crop rotation is only useful for pathogens that overwinter in the field, as opposed to those carried into the field from other locations, and the corn/soybean rotation is often not long enough to adequately reduce soilborne pathogen populations. Repeated use of host resistance genes, without other disease management strategies, induces changes in pathogen populations, allowing them eventually to overcome host resistance. In addition, there are no resistant cultivars available for many of the important soybean diseases, and recent increased use of fungicides is raising concern about the development of fungicide resistance within pathogen populations. Developing alternative soybean disease management tactics would contribute to NCR-SARE’s outcomes and impact sustainable agriculture in the NCR by increasing yield and yield stability, reducing input costs, fostering the use of IPM practices, and helping prevent the development of pathogen resistance.

Crop and cover crop residues, or direct organic matter applications, have affected the level of root and foliar diseases in high value crops, such as lettuce, snap bean, and bell peppers, as well as for crops such as peanut and soybean. Research in 2006 in Southern IL showed that foliar symptoms of SDS and population densities of soybean cyst nematode (SCN) were reduced dramatically following rapeseed cover or green manure crops compared to the non-cover crop control. In addition, a study looking at organic transition strategies showed that specific rotation sequences and the application of certain types of organic matter lowered disease levels over time by enhancement of naturally present disease suppressive microorganisms, inhibition of pathogen activities, and stimulation of host defense mechanisms. Understanding the impact of cover crops on soil microbial populations and root system development could help develop better disease management strategies. Characterization of microbial communities may lead to the discovery of specific disease suppressive microorganisms and to an understanding of community profiles associated with disease suppressive conditions. The selected cover crops are simple to adapt for conventional farmers, as their emergence and large seed size makes planting easy. In addition, canola could provide an option for farmers who decided to grow it in a double crop system for oilseed or forage uses, rather than for the green manure benefits. Demonstrating that cover crop residues can lower disease severity levels would provide soybean farmers with a disease management tool that has the added benefits of increasing soil organic matter content, enhancing nutrient and water holding capabilities, and reducing soil erosion.

Constraints on using cover crops include the economics of their use, concerns about integration with current corn/soybean rotations, and a lack of understanding and incorrect perceptions by farmers. Cover crops are more likely to be used in organic agricultural production.  However, results from this project could help alleviate many misunderstandings and incorrect perceptions by conventional producers, as well. Understanding the impact of cover crop residues on pathogenic organisms and disease processes will enhance our knowledge and aid in the development of sustainable disease management strategies for soilborne and foliar soybean diseases.

            Diseases of soybean regularly cause significant reductions in yield, leading to substantial economic losses. Although yield losses are difficult to measure precisely, one survey-based study estimated that in one year the most common diseases of soybean resulted in a loss of 14,993,800 metric tons worldwide, and 4,962,600 metric tons in the US alone (54, 55). Many of the most important diseases are soilborne, including charcoal rot, Phytophthora rot, Rhizoctonia rot, root knot, soybean cyst nematode, and sudden death syndrome. A few of these diseases are partially managed with disease resistant varieties (10, 17, 32, 33, 45) or crop rotation (33). However, the development of additional management strategies would reduce annual yield losses from these of diseases.

One strategy that could be effective against a broad array of diseases is the induction of disease suppressive soil. A disease suppressive soil is one in which the incidence or severity of a disease on plants growing in that soil is less than what one would see on a plant growing in a conducive soil with a similar pathogen population(3). However, disease suppression is not a qualitative trait, meaning that soils are either suppressive or not. Rather disease suppression is a quantitative characteristic, with all soils falling along a gradient of levels from highly conducive to highly suppressive. Most natural field soils have some degree of natural disease suppression. In many cases the suppression is the result of the activities of microorganisms in the soil. This can be demonstrated by comparing the level of disease that develops on plants growing in natural field soil with the disease level that develops in that same soil after it has been sterilized (21, 41). Most of the time the level of disease developing on plants growing in the sterilized soil will be significantly higher than the level seen on plants growing in the natural, non-sterilized soil.

            There are many mechanisms that may contribute to the soil suppression of plant diseases, including non-pathogenic microorganisms competing with pathogens for nutrients or infection sites, direct parasitism of plant pathogens by antagonistic organisms, and stimulation of a plants ability to resist disease, a phenomenon known as induced systemic resistance. It has been shown that the level of disease suppression of a soil can be altered by changing environmental conditions, which in turn alter the structure and activity of the microbial community in the soil (5, 26).

            One strategy that has received a lot of attention for its potential to elevate the disease suppressiveness of a soil is addition of organic matter. A number of studies have shown that disease levels are reduced following the incorporation of organic matter into the soil (12, 46). However, a survey of the plant pathology literature quickly shows that this is a complex phenomenon, and that simply adding organic matter to a soil will not necessarily lower the amount of diseases that develop on plants grown in these amended soils. Not all organic matter amendments produce the same results, and an amendment that works well in one situation may not work at all in another. Where, when, and how well the addition of organic matter increases disease suppressiveness depends, in part, on the mechanism involved in changing the level of suppression (46).

Organic matter amendments to soil, in the form of residues of the preceding crop, cover crop residues, or direct organic matter applications, have been shown to affect levels of root and foliar diseases in several crops (9, 12, 20, 47). Suppression of soilborne plant pathogens has been observed following additions of certain types of organic matter to soils. In some cases, the mechanism of suppression in these systems was associated with increased microbial activity resulting from the influx of carbon and nitrogen supplied by the incorporated organic matter (42, 43). In a process termed general suppression, it is believed that these organisms compete for nutrients and sites of colonization/infection. There can also be an enhancement of specific suppression, in which there is increased activity of one or a few organisms that directly parasitize, antagonize, or inhibit certain plant pathogens. Specific cropping systems have been shown to alter the associated soil microbial communities (8, 18), and in some cases the population levels of known biological control agents have been enhanced (6).

Certain types of organic matter have been investigated for their ability to release toxic compounds that inhibit or kill soilborne plant pathogens. The incorporation of Sudangrass cover crops has been shown to reduce nematode and fungal diseases of lettuce and potatoes (1, 9, 40, 49). The fact that Sudangrass was able to lower disease levels while equivalent amounts of other types of organic matter were not, and that incorporating two-month old Sudangrass provided better control than three-month old Sudangrass, lends support to the hypothesis that compounds called cyanoglucosides, released by the decomposing grass tissues, are toxic to the pathogens in the soil. Recently, broccoli residues have been shown to effectively control diseases caused by the soilborne fungi Fusarium oxysporum, Rhizoctonia solani, Verticillium dahliae, and others by reducing populations of these pathogens in soil (7, 9, 13, 20, 27, 35, 49). In this case, it is believed that compounds called glucosinolates, released by the decomposing broccoli tissues, are responsible for reductions in pathogen populations. Other pathogen inhibitory chemicals released during the decomposition of organic matter are thought to include ammonia, nitrous acids, alcohols, and aldehydes.

            The use of cover crops as a method of disease control has primarily been investigated for high-value crops, such as apple, potato, and strawberry (22, 27, 28, 48, 51). Research in this area is driven, in part, by the reduced availability of chemical control materials, such as methyl bromide, on which production has depended for many years. The cancelation of the registration of methyl bromide lead to a pressing need and several research projects to develop alternatives. However, the principles learned in the studies on high-value crops should be useful in the management of soilborne diseases in crops, such as soybean, where the application of soil fumigants has never been economically feasible, but the pressures from soilborne pathogens are just as great. There have been a few studies looking at the effects of cover crops in soybean systems. For example, an annual ryegrass cover crop was found to reduce population levels of the soybean cyst nematode (14, 30, 39).

            Foliar disease levels also have been shown to be affected by applications of soil organic matter (47), even for diseases caused by pathogens that do not have a soilborne phase in their disease cycles. Possible mechanisms suggested for this type of disease suppression include changes in a plant’s nutrient status and the phenomenon known as systemic acquired resistance (SAR) or induced systemic resistance (ISR)(46, 47, 56). In these systems, it is believed that microorganisms associated with the roots systemically stimulate the plant’s disease defense system, resulting in lower levels of some foliar diseases.

            Use of cover crops or other organic matter soil amendments to foster the development of disease suppressive soils fit well with other sustainable agricultural practices designed to inhibit soil erosion, improve soil structure, and provide habitats for beneficial organisms. The increased soil organic matter levels resulting from cover crops helps improve several soil factors including compaction, water and nutrient holding capacity, friability, and air and water infiltration (11). Cover crops also have been shown to reduce weed populations through several mechanisms including allelopathy and light competition (23, 31, 57). 

            In a study at the University of Illinois, which evaluated different systems for transitioning from conventional to organic agriculture, crop rotation sequences and organic matter amendments were found to have an effect on some of the naturally occurring foliar diseases of some of the crops included in the study, but no effect on the severity of soilborne root diseases was detected in field or greenhouse evaluations (25). In this study, molecular techniques, including ARISA and rtPCT, were used to analyze microbial community structures and their relationship to the cropping system and amendment treatments. In particular, population levels of a specific group of soil inhabiting bacteria, DAPG producing fluorescent Pseudomonas spp., were evaluated and compared with observed levels of disease suppressiveness to determine if such population levels can be used as indicators of soil health and soil suppressiveness to disease (6, 53).

            A 2006 field trial in southern Illinois reveled that SDS was dramatically reduced in soybean plots following rapeseed as a cover or green manure crop when compared to the level of SDS in plots that did not receive a cover crop. The area under the disease progress curve (AUDPC) was significantly reduced from 157.7 in the fallow to 37.1 in the green manure treatment. Previous studies have shown that residues of cruciferous crops, such as broccoli, reduced the inoculum density of soilborne plant pathogens possibly resulting from the release of toxic compounds from the decomposing residues (20, 34, 35, 44). Like broccoli, the incorporation of cover crop residues of canola have been found to reduce the severity of diseases of wheat and potato (15, 24). The inclusion of canola and rapeseed in the proposed study is intended to determine if these cover crops might be especially efficacious in reducing levels of soilborne diseases in soybean.

 

SARE has funded various aspects of cover crop research (FS07-218, LNE07-252, FNE07-611, LNE88-005 and 007, FNE08-648, LNC07-276 and 282). Some SARE projects have looked at using cover crops for disease suppression or evaluating soil microbe populations for disease control, mainly on ornamental or vegetable crops. FS07-218 evaluated plant vigor with cover crop mulches, but not specific diseases or microbial populations. SW04-113 looked at cover crops impacting soil populations of nematodes and entomopathogenic fungi, LNE01-150 used compost to control grape diseases, and OS07-035 assessed cover crops on Fusarium wilt in watermelon. None of these projects have evaluated cover crops in large-acreage crops, such as soybean, in relation to disease suppression. This study would be the first to look at effects on diseases in this large acreage crop. 

Project Objectives:

The primary objective of this project was to have growers, researchers, and extension personnel collaborated in university and on-farm trials in western, central, and southern Illinois to evaluate the efficacy and feasibility of using cover crops for disease suppression in soybeans. As a result, growers and the academic community would increase their knowledge on the use of four cover crops for suppressing soybean diseases and better understand how cover crops can integrate with current production practices. Growers and researchers would share their results at field days and disease management workshops. Results would be reported on websites, in popular-press and scientific publications, and at research and extension meetings. Participating growers would serve as resources to help educate other growers on the usefulness of using cover crops.

Cooperators

Click linked name(s) to expand
  • Dr. Jason Bond
  • Dr. Loretta Ortiz-Ribbing

Research

Materials and methods:

Trials were conducted over three years at six locations in Illinois, three on university research farms and three on-farm sites. University and on-farms sites were located in east-central, southern, and western Illinois. At each location, replicated strips of cover crops (rapeseed, canola, mustard, or cereal ryegrass) were established in the fall, with a target date of September 15. In the on-farm trials, cover crops were treated with glyphosate, or glyphosate plus 2,4 D, in the spring when the rye plants were 12 to 18 inches tall. The exception was on the Western Illinois University Allison Farm, which is a certified organic operation. At that site, cover crops were killed using tillage to incorporated crop residues into the soil approximately 2 weeks prior to planting soybean. In the on-farm trials, left the cover crops standing after herbicide treatment, and planted into them using no-till planters. The soybean cultivars used in the study were selected based on adaptation for the particular growing region, thus those selected for planting in southern Illinois were different from those grown in western and east-central regions of the state. The soybean varieties used in the on-farm trials were determined by the individual farmers.

Soil samples were collected at the beginning of each growing season to compare pathogen population levels as well as the composition and activity of the soil microbial community among the various cover crop treatments. Soil population levels of soybean cyst nematode were determined through the standard egg count method. Populations of Fusarium virguliforme, the causal agent of sudden death syndrome, and Rhizoctonia solani, the causal agent of Rhizoctonia root and stem rot and seedling blight, and several other fungal pathogens of soybean were determined using soil DNA extraction and Q-PCR analysis methods (19). Microbial community structures were characterized through soil DNA extraction and analysis and automated ribosomal intergenic spacer analysis (ARISA) (2, 4, 16, 36) techniques. Building on our findings from previous research on organic systems, we looked for consistencies of community structures based on cover crop treatment and on observed disease responses.

Spring cover crop biomass, soybean stand, early season root response, foliar disease levels, and yield were measured. Seedling stand counts were measured approximately two weeks after planting. When plants reach the V2-V3 growth stage five plants from each plot were carefully dug from the soil to minimize damage to fine roots, washed, and the root systems were digitally characterized for root length, diameter, and volume using the WhinRhizo root analysis system (25, 37, 38). Levels of Rhizoctonia rot and any foliar diseases also were recorded for these plants.

Visual ratings of any developing foliar diseases, such as Septoria brown spot, downy mildew, frog-eye leaf spot, bacterial blight, and bacterial pustule were taken mid-season, when plants reached the R1 growth stage. Foliar disease levels were evaluated as % incidence or % leaf area affected, depending on the disease. Foliar disease ratings were assessed in randomly selected 1 m2 quadrats, three quadrats per field plot. Levels of root infecting diseases were evaluated as % incidence and percent root discoloration or percent vascular discoloration on five to eight plants per plot using a destructive sampling technique at the R6 growth stage in the rows not used for yield determination.

Soil samples collected from the study locations were used in greenhouse bioassays for determining levels of disease suppressiveness following incorporation of cover crop residues. Field soil samples were divided and each subsample was infested with F. virguliforme, R. solani, or not infested (as a control). These soils were then placed in pots and planted with a soybean cultivar that was susceptible to both sudden death syndrome and Rhizoctonia rot. Root and foliar disease severity levels were recorded 3 to 4 weeks after planting, and disease levels were compared among treatments to determine the level of disease suppressiveness resulting from the cover crop treatments (25, 52).

Analysis of variance (ANOVA) was performed to analyze the effects of  cover crops on soybean stand count, cover crop biomass measurement, foliar and root disease incidence and severity, soybean yield, soil suppressiveness to F. virguliforme and R. solani in the greenhouse, populations of six soilborne pathogens with the aid of JMP Version 9.0.2 (SAS Institute Inc., Cary, NC). For ARISA data analysis, size calling and profile alignment were carried out using GeneMarker V 1.85 software (SoftGenetics LLC, State College, PA). GeneMarker automatically grouped the intergenic spacer region into bins, which were edited manually later to create a panel for comparison of bacterial and fungal community structure. To include the maximum number of peaks while excluding background fluorescence, a fluorescence threshold of 100 fluorescence units was used. The peaks represent fragments of different sizes, and the number of peaks represents operational taxonomic unit (OTU) richness. A bin table containing different sized peaks and their areas was exported from GeneMarker. Analysis of variance was performed to analyze the effect of cover crops on the number of OTU in the soil with JMP. Analysis of similarities (ANOSIM) and non-metric multidimensional scaling (NMDS) were performed with the Primer 6 (Plymouth Marine Laboratory, Primer-E) software program by importing the bin table profile into Primer 6. ANOSIM is a hypothesis that uses Bray-Curtis dissimilarity to test if there is a significant difference in microbial community structures between two or more groups of sampling units. The ANOSIM statistic R is based on the difference of mean ranks between groups (r_B) and within groups (r_W): R = (r_B – r_W)/(N (N-1) / 4). R is ranging from -1 to +1, and value 0 indicating completely random grouping. NMDS is designed to graphically represent the relationship between objects in multidimensional space. The distance between two objects represents the dissimilarity of them, and two closer objects are more similar than those who are further apart. Before ANOSIM and NMDS, the fluorescent signal of each intergenic spacer peak was normalized to account for run-to-run variations in signal detection by dividing the area of individual peak by the total area of peaks detected in each profile, expressing each peak as a proportion of the total fluorescence for each sample.

             Outreach Activities. Growers and researchers participated in the initial planning of the project, as well as mid-project evaluations of procedures and results. Farmers provided guidance of planting and managing the in the field and helped solve problems encountered during the study. One on-farm trial was conducted in each of the three regions of the state involved in this study. Descriptions of the project and updates on results were published in newsletters and popular press publications, often originating from news releases put out by the University of Illinois College of ACES media office. Presentations of project findings were presented at summer field days, extension meeting, and grower conventions, as well as to scientific audiences at professional meetings.

Research results and discussion:

Biomass production by different cover crops was significantly different at all locations in in all three years of the study, with rye producing significantly more biomass than Brassica cover crops. Mustard did not overwinter well in many of the trial locations. Among the three Brassica cover crops (rape, canola and mustard), rape tended to produce more biomass than the other two.

In 2011, soybean stand establishment was significantly reduced in sub-plots inoculated with the fungal pathogen Rhizoctonia solani in the fallow and mustard treatments, while establishment in the rye plots were similar to those in the non-inoculated plots. Stand counts in the canola and rape plots were intermediate between those of the rye and fallow plots. The same level of stand reductions were not seen in 2012 or 2013, but disease severity levels of Rhizoctonia root rot, measured as lesion length, were consistently reduced in the Rhizoctonia inoculated plots previously planted to rye, as compared to those in the fallow plots. Levels in the other cover crop plots were variable from season to season.

There was no observed effect of cover crop treatments on the levels of sudden death syndrome in the plots inoculated with Fusarium virguliforme, but even the fallow-inoculated plots had very low levels of disease. So this was not a good test of the effect of cover crops on this disease.  Other measurements of root and foliar disease severity showed mixed effects of the cover crop treatments. Foliar disease levels on soybean were low on all farms in all three years. Septoria brown spot and bacteria blight incidence was zero in most of the cover crop plots, and there were no significant differences in foliar disease incidence among the cover crop treatments on four farms in 2011 and 2013, and three farms (UIUC, WIU, and Hunt) in 2012. In 2012 at the Ayres Farm, there was less Septoria brown spot in the rye plots than in the fallow plots.

Soybean yield was significantly different over cover crop treatment on the UIUC farm in 2011 and 2012 and on the WIU farm in 2011. On the UIUC farm in 2011, Rhizoctonia root rot was a more severe problem than SDS, and there was a significant reduction in soybean yield within the R. solani infested plots. There were no soybean yield differences over cover crop treatment within F. virguliforme infested or non-infested plots. However, rye maintained soybean yield within R. solani infested plots, while R. solani dramatically reduced yields in the other treatment plots. For the UIUC farm in 2012, yield values in the canola treatment plots were significantly lower than that those in the fallow treatment plots and plots planted to other cover crops. For the WIU farm in 2011, where the plots were not artificially infested with pathogens, the rye no-till treatment significantly improved yields compared yields from the other cover crop treatment plots, while the plots with rye tilled into the soil had the lowest yields.

Significant differences in suppressiveness to F. virguliforme (causal agent of sudden death syndrome [SDS]) and R. solani (causal agent of Rhizoctonia root rot) were observed in greenhouse studies of disease suppressiveness in soil collected from some farms in some years. SDS levels of SDS were lower on soybeans planted into soil collected from the rape treatment plots on the WIU farm and from the rape and rye treatment plots on the Hunt farm in 2012. In 2013, SDS severity was significantly lower on soybeans planted into soil collected from the rye plots as compared to levels on seedlings planted into soil from the fallow plots at the WIU Farm. Rhizoctonia root rot severity was significantly lower on soybean roots planted in soil collected from the rye treatment plots on the Ayres farm in both 2011 and 2012. With the soil collected from the WIU farm in 2012, Rhizoctonia root rot severity was significantly lower on soybeans planted into soil collected from rye, rape and mustard plots than it was on plants grown in soil from the fallow plots. In 2013, the levels of Rhizoctonia root rot were lowest in soils collected from UIUC plots receiving the canola treatment and highest in the soils from the fallow and mustard treatments.

Egg counts of soybean cyst nematodes in the soils collected from the various plots showed that populations of the nematode were consistently lower in soils taken from the rape and rye, and sometimes the canola plots at multiple locations in multiple year.

Using DNA analysis techniques, soil samples were evaluated for population levels of specific soybean pathogens and for the general microbial community structure. While we did find differences in microbial community structures among the different locations used in the study, it was somewhat surprising that we did not find any differences in the microbial community structures among soils from the various cover crop treated plots within a location. This may be an issue of timing of sample collection or the methodology used to determine population levels. We also did not detect differences in populations of the assayed soybean pathogens in the soils collected from the various cover crop plots. Again, this may have been an issue of the time at which the soil samples were collected.

 

Discussion: Of the four cover crops tested in this study, cereal rye and rape had better performance overall than the other two cover crops in terms of winter hardiness, biomass production, maintaining soybean stands and soybean yield in Rhizoctonia infested soils, decreasing severity of Rhizoctonia root rot and incidence of Septoria brown spot, and in reducing soybean cyst nematode population densities. However, the effect of rye and rape on decreasing root diseases severity and foliar diseases incidence, and reducing SCN population was not consistent among locations or over years in the study. The effect of canola and mustard overall was not as prominent as rye and rape on alleviating levels of foliar and root diseases and reducing SCN population, and these result may be caused by multiple factors. First of all, canola and mustard had poor performance in terms of winter hardiness, so the biomass they produced was significantly lower than that of rye and rape.

The effects of cover crop on decreasing severity and incidence of root and foliar diseases was not consistent over different field trials either, and the effect of cover crops on increasing soil suppressiveness to Rhizotonia root rot and SDS in the greenhouse bioassay was not consistent over locations and years. Several studies have been conducted to evaluate the effect of cover crops in suppressing pathogens, and they have often produced mixed results. The result of the field experiments in this study showed that the effect of certain cover crops (rye and rape) was more pronounced in inoculated plots where disease levels were high than in situations with low disease pressure. Thus, cover crops did not show the potential to increase soybean stands, or yield in the absence of disease, but they did play a role in protecting soybean against harm caused by diseases. This result was consistent with several other studies in which the field trials were infested with pathogens to accentuate the effect of cover crops.

One of the problems with this study may have been the selected cover crop species. While the rye crop consistently established well and resulted in good biomass development, the establishment of the Brassica crops was very inconsistent with significant winterkill in several locations.  Another explanation the lack of cover crop effects, especially in the greenhouse bioasssays and DNA analyses, could have been the amount of time between cover crop kill and/or incorporation and soil sampling. The soil samples were collected two weeks after cover crops incorporated in the soil, which may not be at the best decomposition stage to induce suppressiveness to the two root diseases tested. For future studies, it will be interesting to let cover crop decompose longer.

So while results were variable among years and locations, we did find that in some instances the levels of disease on soybeans growing in soils of plots that were previously planted to a cover crop, mostly rye and rape, were significantly lower than the levels on plants growing in the fallow plot soils. Disease levels in the fallow plot soils were never significantly more severer than the levels seen on plants grown in the cover crop soils. Rye, in particular, has the potential to induce soil suppressiveness to Rhizctonia root rot, and sometimes to sudden death syndrome. Both rape and rye were found to consistently reduce egg counts of the soybean cyst nematode.

Research conclusions:

The information generated by this project is promising. There is support for the idea that cover crops can reduce both root and foliar diseases of a following soybean crop and result in increased yield levels, especially in situations where Rhizoctonia root rot is a problem. This information will encourage soybean farmers in the Midwest to consider adding cover crops to their rotation schedules, resulting in less soil erosion and increased soil health.

Farmer Adoption

The farmer/cooperators involved with the project were asked to provide feedback on their experience of using cover crops in the study and their likely hood of continuing to use them in their production systems. One of the farmers was very positive, especially with the rye cover crop performance, and he indicated that he would definitely increase the amount of area that he will plant to rye cover crops in the future. This grower also like the benefits of the rape cover crop when it successfully established, but found that it was difficult to get good stand establishment consistently. Another farmer saw the benefits of using cover crops, but also mention that they were a “two edged sword”, in that if conditions were good he found them to be very beneficial. However, if the timing is off on termination or if there are drought conditions then the effects can be negative. The third farmer already uses cover crops on most of his acres and said that he will not change his practices as a result of participating in this study. The farmers commented that there needs to be more work on selecting the right cover crop for the location and situation.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:

Wen, L.; Hartman, G. L.; Eastburn, D. M. 2012. Suppression of soybean diseases through the use of cover crops. Phytopathology 102:134.

 

We are currently preparing a manuscript for publication in a peer reviewed journal. The working title for the manuscript is “Suppressing soybean diseases with fall planted cover crops”.

 

Due to restructuring of University of Illinois Extension during this project, the proposed outreach activities were changed.  However, the findings from this research were (and still are) disseminated to growers and extension personnel in several ways. In Illinois, the results of the study were discussed directly with growers at University of Illinois field days including Agronomy Day in Urbana (August 16, 2014 and August 15, 2013), the Allison Farm Organic Field Days (August 2011, 2012, 2013), and field days in southern Illinois, plus at University of Illinois winter extension meetings in several locations throughout the state. 

            During this project, Loretta Ortiz-Ribbing was a new faculty member at the University of Wisconsin in River Falls. She used this platform to make students and fellow faculty aware of this research on disease management and to discuss the use of cover crops as an alternative soybean disease control tactic in an effort to reduce the development of fungicide resistance among pathogen populations. Results were shared with twenty-five students in Sustainable Agriculture (CROP 368; Spring 2012 and 2013 combined), seven in Organic Production (CROP 46; Fall 2012), fifty-three in Weed Control (CROP 345; Spring 2011, 2012, and 2013 combined), and fifteen in Integrated Pest Management (IPM in Fall 2012) courses over three years.  The topic of cover crops and this research project in particular, always produced an engaging discussion and gave students an opportunity to discuss and share information about their own experiences using cover crops in various capacities on their home farms. A total of approximately 100 students had the opportunity to engage and learn from this project’s results.

            In addition, in Minnesota and Wisconsin, Ortiz-Ribbing presented a seminar at the University of Minnesota (June 2014) for the Department of Plant Pathology that shared the results of our cover crop project with about 22 UMN faculty, students, and extension members.  Over the past, three years, Ortiz-Ribbing has shared this research project and preliminary results by networking and face-to-face conversations and by participating in group discussions with growers, researchers, industry reps, and extension at the 2011, 2012, 2013, and 2014 MOSES (Midwest Organic and Sustainable Education Service) Organic Conferences in La Crosse, WI, the 2014 APS meeting in Minneapolis, MN, as well as at the University of Wisconsin Extension Cover Crop and Soil Health Forum in Durand, WI and the University of Minnesota Fall Cover Crop Field Day in New Richland, Minnesota on the Querna Farm, plus with colleagues at the Minnesota Department of Agriculture.  Over the past year this interaction has made approximately 75 people aware of this research and some results.

            Findings from this study were presented at scientific meetings (American Phytopathological Society 2013; Resilient Agriculture Conference 2014; W3147 (Managing Plant Microbe Interactions in Soil to Promote Sustainable Agriculture) annual meetings in 2011, 2012, and 2013.  

Project Outcomes

Recommendations:

Areas needing additional study

We had variable results with the various cover crops that were used in the study, partially because of issues with stand establishment. Additional work needs to be done to select the best species and varieties of cover crops that would be most likely to result in disease suppression. Modifications of techniques and timing of sample collection may allow for better determination of the effects of the microbial community on the development of disease suppressing resulting from cover crop use. 

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.