Soybean Cyst Nematode

Watch for Soybean Cyst Nematode
by Ron Kuck, CCE Cayuga County Agriculture Program Educator
Source: Cayuga County e-Ag Alert March 2021 (Full article here in PDF format)

Jaime Cummings, Field Crops Coordinator with the New York State Integrated Pest Management Program presented a Soybean Cyst Nematode (SCN) Workshop. SCN was first discovered in New York State in Cayuga County in 2016. We can now say SCN is widespread in NY and it is now time to expand education and intensive SCN management efforts.

Why do we care? The SCN is the #1 yield-robber of soybeans. (see chart). Without symptoms, there can be 10-30% yield loss. With severe symptoms, there can be 50% loss; you don’t want to get to this point. Other management challenges are that eradication isn’t an option and SCN are long-lived.

It’s easier (and less expensive!) to maintain low or moderate SCN levels than it is to reduce higher populations. Fortunately, most SCN confirmations in NY were at ‘Low’ population densities. According to SCN Diagnostics Laboratory: <500 eggs = low, 500-10,000 = moderate, >10,000 = high.

SCN symptoms are vague or invisible. Some questions to help determine if you are impacted by SCN:

• Do you have fields that are consistently low-yielding?
• Do you have fields with a history of Sudden Death Syndrome?
• Areas of fields prone to flooding and/or compaction?

So what should I do if I suspect SCN?
Testing is important, but low populations are difficult to detect. So, focus your sampling, especially in fields with a history of Sudden Death Syndrome. Use general, random sampling, in-season visual checks for cysts. Dig (not pull) plants, gently remove soil and look closely: Mid-July or Early-September is best time.

Once confirmed in a field, test your fields to know your numbers. One cyst can contain up to 250 eggs! 

• Pay attention to populations = egg counts
• Test known infested fields once every 3 years
• Record and track egg counts
• Follow management recommendations. IPM is the best approach to managing SCN.

TEST, TEST, TEST

• A negative result doesn’t mean you don’t have SCN
• Could be very low population, or you just missed them

Rotate to non-host crops (corn, alfalfa, clover, small grains)

• Best and most cost effective

Rotate resistant varieties

• Emphasis on rotate-nematodes are becoming resistant

Use nematode seed treatments when necessary! Not needed in most NY fields-yet!

• Results will vary among treatments, among locations/soil types and growing seasons
• Treatments get best ROI in situations with high SCN infestations

Continue testing with a reliable lab. NYSIPM uses and recommends SCN Diagnostics, University of Missouri, 573-884-9118, scndiagnostics@missouri.edu

• $25 per sample
• Very fast turnaround
• Egg counts
• Can also do race-type testing
• Very responsive to questions
• Specialize in SCN testing.

The New York State Department of Agriculture and Markets and New York Corn and Soybean Growers Association fund soybean cyst nematode surveys in NY.

SCN Keeps Spreading, Economic Losses Increasing
By Julianne Johnston: jjohnston@morganmyers.com, 319-233-0502
Source: The SCN Coalition (Full article here in PDF format)

Waukesha, Wis. (Jan. 25, 2021) – “In just the past three years, soybean cyst nematode (SCN) has spread to 55 new U.S. counties in 11 states,” says Greg Tylka, Iowa State University (ISU) nematologist and co-leader of The SCN Coalition. “The most damaging soybean pathogen, SCN has also infested 24 new counties and rural municipalities in the Canadian provinces of Manitoba, Ontario and Quebec.”

Periodically, Tylka surveys plant health professionals at universities as well as state and provincial departments of agriculture in the U.S. and Canada about SCN’s spread.

“We compared the 2020 results with the 2017 survey. The results reveal steady expansion of the distribution of SCN throughout North America,” Tylka says. “And the pest will almost certainly continue to spread among and within soybean-producing areas.”

New York has greatest number of new infestations

At 29, New York reported the largest number of newly infected SCN counties in the United States. Gary Bergstrom, a plant pathologist at Cornell University, says the first discovery of SCN in the state in 2016 led to an intensive SCN survey by Cornell Cooperative Extension educators coordinated by the state’s IPM program.

“SCN is now widespread in New York,” says Bergstrom. “Soybean growers are fortunate that in most fields where SCN has been detected, population densities are low, although it’s concerning that a few counties had higher numbers.”

Bergstrom is not surprised SCN continued to spread across New York given its steady expansion of soybean acres over the last few decades. “This should be a wake-up call for soybean growers in New York and neighboring states,” he adds. “SCN is coming to you if it’s not already there.

“Growers are asking more questions about SCN-resistant varieties, nematode-protectant seed treatments, and soil testing for SCN,” he adds. “Coalition resources are invaluable in our efforts to educate soybean growers about the importance of active management. Our next step is studying the virulence of SCN populations to help growers select SCN-resistant varieties.”

Economic loss from SCN $1.5 billion annually

Also in 2020, plant pathologists from several land-grant universities published research examining the economic losses of soybean diseases. Using a variety of statistical approaches, the researchers estimated economic impacts of 23 common soybean diseases in 28 soybean-producing states in the U.S. from 1996 to 2016. The result: SCN caused estimated yield losses of nearly $32 billion during that time. That’s more than $1.5 billion annually.

“The magnitude of economic loss caused by SCN is due to three factors,” Tylka says. “It’s widespread and expanding distribution, its capacity to survive long term in the absence of soybeans, and its ability to consistently reduce yields.”

Management options to protect soybean yields

If SCN is left unmanaged, population densities and the potential for yield losses steadily increase. Unfortunately, SCN often goes unnoticed in fields because aboveground symptoms of damage and yield loss may not be visible.

“That’s why scouting fields and soil sampling are two key management tools, because it’s harder to reduce damaging SCN population densities than to keep them in check. The SCN Coalition also recommends growing soybean varieties with resistance to SCN in rotation with nonhost crops, and using nematode-protectant seed treatments,” Tylka says.

He encourages soybean growers to look for varieties that don’t contain resistance genes from the PI 88788 breeding line. “PI 88788 has been used in the vast majority of varieties for most of the last 30 years. That’s led to SCN populations increasingly reproducing on PI 88788 varieties and decreasing yields.” A list of varieties with Peking SCN resistance is available here.

Tylka’s 2019 soybean variety trials for ISU Extension showed the problem with PI 88788. In the trials, soybean varieties with the Peking source of resistance yielded 22 bushels per acre more than varieties with the PI 88788 SCN resistance.

About The SCN Coalition

The SCN Coalition is a public/checkoff/private partnership formed to increase the number of farmers who are actively managing SCN. Our goal is to increase soybean farmers’ profit potential and realize higher yields. Partners in The SCN Coalition include university scientists from 28 states and Ontario, grower checkoff organizations including the North Central Soybean Research Program, United Soybean Board and several state soybean promotion boards, and corporate partners including BASF, Bayer, Growmark, Nufarm, Pioneer (Corteva), Syngenta, Valent and Winfield United. 

Soybean Cyst Nematode: The Greatest Threat to NY Soybean Production is Here to Stay. Now What?
By: J. Cummings, K. Wise, and M. Zuefle - NYS Integrated Pest Management Program E. Smith, M. Hunter, M. Stanyard, A. Gabriel, K. Ganoe, J. Degni, J.L. Putman, K. O’Neil, J.A. Putman, J. Miller, and M. Lund - Cornell Cooperative Extension M. Dorgan - NYS Department of Agriculture and Markets
(Full article here in PDF format)

The soybean cyst nematode (SCN) is the number one pest of concern in U.S. soybean crops, causing an estimated $1.5 billion in annual losses. Considered a ‘silent’ yield-robber, SCN can cause 10-30% yield loss without any obvious, above-ground symptoms. SCN hadn’t been considered a pest of concern for NY soybean growers before it was first confirmed in Cayuga County in 2016. Even then, it wasn’t a priority consideration. However, based on recent findings, NY soybean (and dry bean) growers can no longer afford to ignore this threat.

The NY State Integrated Pest Management Program, in collaboration with Cornell Cooperative Extension field crops specialists, and funded under a grant from USDA-APHIS Plant Protection Act section 7721 administered by NY State Department of Agriculture and Markets, coordinated a statewide SCN survey in 2019 as part of a soybean commodity survey to test 25 fields. This testing revealed an additional six counties with fields positive for SCN. Those results prompted a continuation and expansion of a SCN survey in 2020 with additional funding from the NY Soybean Checkoff dollars to provide testing for 100 fields statewide. The 2020 survey identified an additional 22 counties with fields positive for SCN. These surveys, along with shared observations from individual testing efforts have now confirmed SCN in a total of 30 counties across NYS, and it is safe to assume that SCN will likely be identified in all soybean producing counties in NYS with continued testing in future years.

Figure 1. The progression of confirmation of the soybean cyst nematode throughout NY State. Counties shaded in green had fields tested with negative results, and counties shaded in red have at least one field confirmed positive for soybean cyst nematode. (All testing was conducted by the SCN Diagnostics Laboratory at the University of Missouri in 2019 and 2020)

Now that we know that SCN is here, and is widespread across NYS, what’s next? Unfortunately, eradication is not an option, but reduction and maintenance of low populations is. Management strategies depend on SCN population levels, which can vary significantly from field to field. Regular testing for this nematode will help you determine your best plan of action for management. Fortunately, most of our positive SCN detections have been in the “low” category, but we found four fields with “moderate” levels and one field with “high” levels of SCN. For reference, based on test results (according to University of Missouri SCN Diagnostics Laboratory), “An egg count of <500 eggs is considered low. An egg count of 500-10,000 is considered moderate. An egg count >10,000 is considered high”. Those egg counts are based on what they find in one cup of soil. Finding a field in NYS with an egg count of 20,000 was quite surprising this year, and it translated to measurable yield loss for the grower. This means we can’t afford to ignore this pest, and we need to start actively managing SCN before our “low” results all become “high” results.

Figure 2. Female SCN nematodes produce ‘cysts’ on soybean roots, which contain the eggs (a). These cysts, when dislodged from the roots, are distributed within the soil (b). The cysts contain approximately 200 eggs each (c). (Images courtesy of G. Yan, S. Markel and E. McGawley, via the SCN Coalition)

It’s much easier to stay ahead of this pest than to try to manage high numbers.Fortunately, our number one management strategy is crop rotation. Once you know you have SCN in a field, the worst thing you can do is grow soybeans continuously. We are lucky to have a number of non-host crops available for rotation, including corn, small grains, clover, alfalfa, and forage grasses.Studies have shown that a one-year rotation to corn may result in up to a 50% reduction in SCN populations the following year.The next best option for managing SCN is by selecting and planting SCN-resistant soybean varieties, and rotating those varieties that you plant.More on that later.For dry beans, however, resistance is not an option, and rotation is even more critical.The third management option is the use of nematode-protectant seed treatments.There are a number of these products available, and most have shown promising results.However, those seed treatments will be most cost-effective in situations where there is high SCN pressure.So, for the vast majority of acreage in NY, based on our current survey results, the seed treatments can be an expensive option with limited benefits for many of our growers.But, that may change as SCN testing expands and we find more moderately to highly infested fields.Of course, an integrated pest management (IPM) approach will provide the best management results, by combining all available management tools.

It's impossible to talk about SCN management without mentioning resistance. I said previously that you should consider selecting and planting SCN-resistant varieties, and that you should rotate those varieties. Unfortunately, SCN has been evolving and developing resistance to the traits most commonly available in commercial soybean varieties for decades. Slowly, SCN has developed different races that can overcome the resistant soybean varieties. This pest is highly adaptable. That’s why it’s important not to plant the same soybean variety, even if it’s labeled as ‘resistant’, in the same field repeatedly. Similar to chemical modes of action (like herbicides), it’s critical to rotate your tools to avoid, or minimize, resistance development. For more information on this topic, please visit the SCN Coalition website, where they have an abundance of resources available on this topic. Luckily, a number of major seed companies have soybean varieties in the pipeline with novel sources of SCN resistance, and we look forward to the new options.

Figure 3. SCN cysts are tiny, but can be seen on soybean roots with or without magnification. Much smaller than nodules, the cysts appear as whitish-yellow specks along the roots. (Images courtesy of G. Tylka via the SCN Coalition)

Moving forward, we hope to continue providing statewide SCN-testing services to growers through funded surveys. Please contact your local Cornell Cooperative Extension specialist if you suspect you might have SCN on your farm. Continued monitoring through testing will help us understand our populations of SCN, to help make the best management decisions. Let’s work together to maintain mostly low to moderate populations of this potentially devastating pest.

Additional Resources and Related Articles:

Soybean Cyst Nematode Now Confirmed in Six Additional Counties in NY

Soybean Cyst Nematode Now Confirmed in NY

Sudden Death Syndrome and Soybean Cyst Nematode in Soybeans

Fall is the Time to Test for Soybean Cyst Nematode

SCN Coalition website

Cornell’s SCN Web Page

Soybean Cooperative Agricultural Pest Survey:Vigilance Against Potentially Invasive Species

Last updated March 4, 2021