Monitoring Soybean Cyst Nematode HG Types in the Eastern Corn Belt

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Background and Rationale

Soybean cyst nematode (SCN; Heterodera glycines) is a major yield-reducing pathogen of soybean production in North America. It has spread to practically all important soybean production areas of the U.S. and Canada, and is reaching economic levels in more areas.
SCN may decrease yields substantially without inducing obvious symptoms. Studies have shown that in SCN-infested fields, yields can be reduced by over 30 percent without visible above-ground symptoms.
The most important management tactic for SCN during the years since its establishment as a yield-limiting pest in North America has been selection of soybean varieties with genetic resistance to SCN.
Most resistant soybean varieties use the resistance source PI88788. However, SCN Types that can overcome PI88788 resistance are becoming more widespread throughout the eastern Corn Belt.
SCN populations are genetically diverse and have historically been separated into races by their ability to reproduce on soybean tester lines. However, a newer classification system called the HG type test has been widely adopted. The term “SCN race” referred to individual nematodes but “HG type” reflects the entire population found in a field.
Results of the HG type test indicate on which resistance sources a population of SCN found in a field would still be able to feed and reproduce (Table 1). For example, an HG type of 2 means the population can reproduce on PI88788 soybean varieties while HG type 1.2 can reproduce on both PI88788 and Peking varieties. Type 0 is well controlled by all resistance sources including PI88788 (Tylka, 2006).

Table 1. Indicator lines for HG type classification of SCN.

Table - Indicator lines for HG type classification of SCN.

Objectives

In order to determine how to best steward the SCN resistance traits, Pioneer field agronomists sampled soybean fields across the eastern Corn Belt in 2018 and 2019 to detect the presence and HG type of SCN populations.

Study Description

In 2018, soil samples were taken from Pioneer soybean product knowledge plots across Illinois, Indiana, Ohio, and Michigan.
Samples were submitted to the University of Illinois Plant Clinic for Mini HG tests. The Mini HG test uses the three tester lines that are available in commercial soybean varieties: PI548402 (Peking); PI88788, and PI437654 (Hartwig or CystX). A female index (FI) is calculated by comparing reproduction on the resistant line to that of a susceptible cultivar, ‘Lee.’ A FI over 5 indicates resistance.
In 2019, samples were collected again from the original geography plus New York and Pennsylvania.

Results - 2018

65% of samples were HG Type 2, indicating increased ability to reproduce on varieties with PI88788 resistance (Table 2).
5% of samples were HG Type 1.2, indicating increased ability to reproduce on varieties using both PI88788 and Peking resistance
(Table 2).

Map - Distribution of HG types found in soybean plots in 2018.

Figure 1. Distribution of HG types found in soybean plots in 2018.

Table 2. 2018 SCN survey HG type results.

Table - 2018 SCN survey HG type results.

Preliminary Results - 2019

As of November 2019, egg counts had been completed for submitted samples.
SCN infestations were found widely throughout the eastern Corn Belt.
SCN infestations were generally higher in Illinois, Indiana, and Michigan than in Ohio, Pennsylvania, and New York.
Samples with more than 40 eggs per 100cc of soil will be tested to determine HG Type with results expected in early 2020.

Map - SCN egg counts by location in 2019.

Figure 2. SCN egg counts by location in 2019.

Conclusions

SCN populations capable of overcoming PI88788 resistance are found in the eastern Corn Belt.
Although strong yields are still possible from soybean varieties using PI88788 resistance, this trait needs to be stewarded in order to preserve it for future use.
Fewer SCN populations can overcome Peking resistance but there are some present in the eastern Corn Belt. Stewardship of Peking resistance needs to start now

What you can do:

Test soybean fields for SCN.
If no infestation is found, use good management practices and rotate a combination of resistant or susceptible varieties in the field.

If SCN is found:

Rotate to non-host crops such as corn.
Consider using a nematode protectant seed treatment such as ILeVO^®.
- Nematicide seed treatments are intended to supplement current SCN management strategies, not replace them. Seed treatments should therefore be used in coordination with SCN-resistant varieties and rotation to non-host crops (Bissonnette and Tylka, 2017).
- The LumiGEN™ system offering includes ILeVO^® fungicide/nematicide seed treatment, which has activity against SCN.
- A Pioneer study including 193 on-farm trial locations found an average yield response of 4.9 bu/acre in high SCN fields when ILeVO fungicide/nematicide seed treatment was added to the standard fungicide and insecticide seed treatment package (O’Bryan and Burnison, 2016).
Control alternate weed hosts such as henbit, purple deadnettle, field pennycress, shepherd’s purse, small-flowered bittercress and common chickweed.
Rotate resistant varieties
- If you have type 0 SCN, change varieties in a field each soybean rotation.
- If you have type 2 or type 1.2 SCN, consider rotating to a Peking-source variety every other soybean rotation if agronomically appropriate Peking varieties are available.
- Twelve Pioneer^® brand A-Series soybean varieties with Peking resistance are available for the eastern Corn Belt for 2020.
- Variety and resistance source rotation is even more important in continuous soybean production.
Consult your university soybean extension specialist for specific management recommendations for your state.

References

Bissonnette, K.M., and G.L. Tylka. 2017. Seed Treatments for Soybean Cyst Nematode. Iowa State University Extension. Crop 3142.
O’Bryan, K., and M. Burnison. 2016. Performance of Soybean Seed Treatments Against SDS and SCN in On-Farm Trials. Pioneer Agronomy Research Update.
Tylka, G. 2006. What's your type?: An HG type test for SCN populations. Iowa State University Extension Integrated Crop Management News.

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ILeVO^® is a registered trademark of Bayer. Components of the LumiGEN™ system for soybeans are applied at a Corteva Agriscience™, Agriculture Division of DowDuPont production facility, or by an independent sales representative of Corteva Agriscience or its affiliates. Not all sales representatives offer treatment services, and costs and other charges may vary. See your sales representative for details. Seed applied technologies exclusive to Corteva Agriscience and its affiliates.

The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Multi-year and multi-location is a better predictor of future performance. Do not use these or any other data from a limited number of trials as a significant factor in product selection. Product responses are variable and subject to a variety of environmental, disease, and pest pressures. Individual results may vary.

Author: Mary S. Gumz, Ph.D.
November 2019