Soybean cyst nematode (SCN) is a very important disease for soybean production and can cause 15-30% yield loss without obvious above-ground symptoms. Managing SCN is crucial to reduce economic losses for farmers. Cover crop acreage is increasing in the northern Great Plains due to improving soil quality and providing ecosystem benefits. In addition to providing soil and ecosystem benefits, if these crops can be used to manage SCN, that would be an additional benefit for farmers. Previous studies have shown that cover crops could suppress plant-parasitic nematodes such as root-knot nematode, sugar beet cyst nematode, and potato cyst nematode. However, the effectiveness using cover crops to control SCN is not well studied. With the funding support from the Council, we have evaluated forty-one cover crop species/cultivars for host suitability to SCN. Thirty-one of the crop species/cultivars tested did not support SCN reproduction and were classified as non-hosts. Twenty of the crops were evaluated for SCN reduction in microplot experiments. All the non-host crops tested were able to reduce SCN numbers in infested soils. Cover crops may reduce SCN populations by three mechanisms, such as non-host with encouraging SCN egg hatching, acting as a trap crop with stimulating penetration of plant roots by SCN juveniles, and producing toxic biochemical compounds. To date, there have been few published scientific studies of how different cover crops interact with SCN through hatching and penetration. To identify effective cover crops, the interaction of cover crops and SCN should be investigated for better managing SCN.

1. Evaluate the effects of ten cover crop species/cultivars on hatching of soybean cyst nematode juveniles.
2. Evaluate the effects of ten cover crops species/cultivars on penetration of soybean cyst nematode juveniles.

The effects of ten cover crops on hatching and penetration of SCN juveniles will be disclosed and the rankings of these cover crops for their abilities to stimulate hatching and penetration to reduce SCN numbers will be summarized and made available to soybean farmers.

Updated November 29, 2020:
Identifying Effective Cover Crops for Management of Soybean Cyst Nematode

PI: Guiping Yan, Ph.D.
Collaborators: Drs. Marisol Berti, Sam Markell, and Berlin Nelson

Objectives of the research

1. Evaluate the effects of ten cover crop species/cultivars on hatching of soybean cyst nematode juveniles.
2. Evaluate the effects of ten cover crops species/cultivars on penetration of soybean cyst nematode juveniles.

Completed work

Soil samples were collected from a field with SCN in Richland County, North Dakota based on our previous work. All the soil samples were pooled together and thoroughly mixed to distribute nematode evenly throughout the soil. After thorough mixing, sub-samples were taken to extract SCN cysts and then those cysts were crushed to release eggs which were quantified under a microscope to determine the initial population density of SCN. The well-mixed field soil was then used for the growth chamber experiment.

Ten entries of cover crops including Alfalfa (Bullseye), Daikon radish (Eco-till), Faba bean (Petite), Foxtail millet (Siberian), Oilseed radish (Concorde and Control), Red clover (Allington), Turnip (Purple top), White mustard (Master) and Winter rye (Dylan) were selected for the experiment using the SCN-infested field soil. The susceptible soybean (cv. Barnes), common rotational crop corn (DKC44-13), and a non-planted control were also included. All entries were replicated four times and were planted in plastic cone-containers each containing an average 163 g of soil in a growth chamber maintained at 27 °C (Figure 1). Those entries were planted on August 26 in two sets each containing all the entries, and were terminated 15 days after planting and 30 days after planting, respectively. After termination of the experiment, plant parts above soil surface were removed and all the soil samples along with plant roots were stored in a cold room (4°C) until nematodes were extracted and roots were stained.

Plant roots were gently separated from the soil before the cyst and juvenile extraction. Cysts were extracted from the soil from each cone-container using the sieving and decanting and sugar centrifugal floatation methods. In the meantime, hatched juveniles were also extracted from soil. Extracted cysts were crushed to release eggs which were then counted under a microscope. The separated roots were washed carefully and stained with red food coloring dye (Figure 2). Those stained roots are being observed under a microscope and second-stage juveniles and nematodes in other life stages inside the stained roots are being quantified.

Preliminary results

The initial SCN population density in the infested field soil collected from Richland County, ND was 2,300 per 200 g of soil (˜ 100 cc soil). The average SCN number in each cone-container was 1,877 eggs and juveniles since each cone-container holds approximately 163 g of soil on average.

Out of ten cover crops used in this experiment, nine entries including Alfalfa (Bullseye), Daikon radish (Eco-till), Faba bean (Petite), Foxtail millet (Siberian), Oilseed radish (Concorde and Control), Red clover (Allington), White mustard (Master) and Winter rye (Dylan) did not show any reproduction of SCN from the field. Also, the common rotational crop corn (DKC44-13) did not support any SCN reproduction. These results indicate that these crops are non-host of SCN, which supports the results obtained from our previous study. One cover crop Turnip (Purple top) showed limited reproduction of SCN with the numbers of white females from 2 to 8 suggesting poor host ability. The susceptible soybean cultivar Barnes showed high reproduction with white females from 216 to 262. Similarly, all the tested cover crops along with corn and non-planted control produced smaller numbers of SCN eggs and second-stage juveniles in the soil as compared to soybean (Barnes) at 30 days after planting.

The results of host range of cover crops to SCN from our previous work have been summarized and presented in a manuscript which was published in the journal, Crop Protection in 2020. The results of effects of cover crops on population reduction of SCN were also summarized and now are in press in the journal, Plant Disease, to disseminate the research findings.

Work to be completed

As the stained roots are being observed under a microscope, we will identify and quantify second stage SCN juveniles and other life stages inside the roots. The quantification of the numbers of SCN inside the roots along with the numbers of second-stage juveniles from soil and the numbers of SCN obtained from cyst crushing will help us accomplish the objectives of this project to identify effective cover crops. We will determine the hatching ability for each of the cover crops and their ability to allow juveniles to penetrate the roots. The data obtained will be analyzed using the software SAS 9.4. The ability of cover crops to enhance SCN egg hatching and penetration by juveniles will be summarized after data analysis. The performance of these cover crops will be ranked and made available to the soybean farmers at field days, extension meetings, or in extension publications.

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Updated June 30, 2021:

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IDENTIFYING EFFECTIVE COVER CROPS FOR MANAGEMENT OF SOYBEAN CYST NEMATODE

EXECUTIVE SUMMARY

NORTH DAKOTA SOYBEAN COUNCIL
JUNE 2021

Dr. Guiping Yan, Principal Investigator, Dept. Plant Pathology, NDSU

Research Conducted
Ten cover crop species and cultivars were evaluated for their effect on hatching of soybean cyst nematode (SCN) eggs and penetration of plant roots by juveniles, along with a rotational crop corn, a susceptible soybean, and an unplanted infested soil (fallow). All the entries were planted in two sets in cone-tainers each with 100 cm3 of infested soil collected from a soybean field in ND. Crops were harvested 15 and 30 days after planting (DAP). Plants roots were stained with food coloring dye to visualize nematodes inside the roots for penetration. Soil from each cone-tainer was processed to extract and quantify SCN juveniles and eggs for hatching.

Why the research is important to ND soybean farmers
Many cover crops were evaluated for their hosting and population reduction on SCN, the major yield-limiting biotic factor of soybean. Cover crops showed the potential to be used as an alternative means to manage SCN but their effect on biology of SCN for population reduction are not well known. This research provides a better understanding of effects of cover crops on biology of SCN for identifying effective cover crops.

Final findings of the research
Faba bean had a significantly higher number of juveniles in soil and inside the roots than other cover crops and fallow 15 DAP, suggesting greater SCN hatching. Significantly more SCN juveniles penetrated the roots of faba bean 15 DAP but subsequently, those juveniles were significantly reduced 30 DAP. Red clover, alfalfa, and foxtail millet had very low juvenile penetration on roots, indicating they may starve the hatched juveniles in the absence of suitable hosts which results in ultimately the death of juveniles. The significant effect of brassica crops (daikon radish, oilseed radish, white mustard) on hatching and penetration of SCN was not observed, suggesting a role of their bio-fumigation property on SCN population reduction.

Benefits/Recommendations to North Dakota soybean farmers and industry
All cover crops except turnip reduced the SCN population in infested soil. These crops can be used as cover crops or rotational crops in infested fields to manage SCN. Faba bean greatly enhanced the hatching of SCN eggs and penetration of roots by juveniles without supporting reproduction, suggesting a great potential to serve as a trap crop for SCN management. The research findings will be useful for farmers to select effective cover crops for reducing SCN damage to improve soybean production in infested fields in ND.

This proposed research will investigate the interaction of different cover crops and SCN. Through this mechanism study we aim to identity cover crops that are capable of greatly stimulating hatching and penetration of SCN juveniles to decrease SCN numbers in soil for management of SCN. The proposed research findings will be useful to navigate the selection and use of different cover crops for farmers and the new sources that should be introduced to ND. Such information is important to help farmers make the best management strategies using cover crops to reduce damage caused by SCN to increase soybean yield.