In 2021, Manitoba saw its first field with symptoms, although the first finding of the nematode dates back to 2019. By the time symptoms were observed, surveillance maps suggested that five municipalities out of 18 being monitored in central and eastern Manitoba had confirmed presence of SCN.

Why it matters: Varieties resistant to soybean cyst nematode and white mould could help growers meet the export potential of identity preserved soybeans into overseas markets.

The two diseases can be especially troublesome in food-grade soybeans, also a market that has more traction in the east.

Istvan Rajcan, a soybean breeder at the University of Guelph, is in the final year of a three-year program to develop higher-yielding, disease-resistant, food-grade soybeans. Funding is coming from the Grain Farmers of Ontario and the Ontario Agri-Food Innovation Alliance, a collaborative venture of the University of Guelph and the Ontario Ministry of Agriculture, Food and Rural Affairs. The program began in May 2021 and will finish in April 2024.

Private sector seed companies typically release new varieties with a lifespan of two to six years, but food-grade soybean varieties generally have a longer run with food manufacturers and buyers, mostly because of quality demands.

“The replacement of GM varieties by the private sector is frequent and fast, but I’m not sure how deliberate that is,” says Rajcan.

“In our case, the IP (identity preserved) market is a little different in that a lot of the IP soybeans produced in Canada are exported to Asian and other foreign markets, and once an IP variety gets a name based on its food-grade qualities, the buyers tend to keep asking for the same. They like to work with what they know.”

Finding the right genes

Although it’s a three-year project, Rajcan said he won’t have high-yielding food-grade varieties with nematode and white mould resistance ready to commercialize by next year.

The funding allows his team to use molecular markers to find resistance genes faster. Rajcan notes there are two major genes for cyst nematode and one recently discovered major gene for white mould.

“They’re not in the same variety, so I need to take a high-yielding soybean variety that has no resistance to either disease and first cross it with a source of SCN resistance to incorporate those two major genes,” he said.

“In the next round of crosses, which could come years later, I have to bring in the gene for white mould resistance into that same OAC variety that became SCN-resistant. In some instances, a variety resistant to SCN has been crossed to one resistant to white mould already.”

That takes years to develop, and they don’t cover the spectrum of resistance to the two diseases. Minor genes are also required.

“We still need those minor genes to contribute to higher levels of resistance,” says Rajcan. “The more genes one works with, the longer it takes to bring them all together. We call that gene pyramiding, where we’re building a variety that’s high-yielding, resistant to white mould and SCN and other stresses.”

The industry perspective

The food-grade sector is always looking for export opportunities. For Brian Innes, the focus for food grade soybeans is a delicate balance between maintaining competitiveness in the market and working to enhance quality parameters in future varieties.

“As an organization and as an industry, we are focused on how we maintain and improve the competitiveness of food-grade soybean genetics for farmers,” says Innes, executive director of Soy Canada.

“The fit for Istvan’s research is helping address key diseases with genetics to ensure we’re keeping up with commodity GM soybeans.”

Unlike traited soybeans, demands for quality and consistency, balanced against the farmer’s need for profitability, redefine how quickly food-grade soybean varieties can be commercialized. Successful varieties need to deliver end-use quality and be accepted by buyers, as well as perform well for farmers .

“The competitiveness of food-grade varieties for farmers is important for us to work on collectively, as an industry and as Soy Canada, and how we support our seed companies and exporters,” says Innes.

“Helping to increase the speed of adoption of new varieties which bring new agronomic traits, such as resistance that Istvan is working on, is a major priority for the industry to maintain and grow our food-grade specialty acres.”

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Soybean cyst nematode (SCN) is already a serious pest in the soybean belt of the American Midwest.

It is believed to have originated in Asia, where soybeans also originated, according to plant pathologist Greg Tylka of Iowa State University.

Why it matters: The microscopic parasites have been known to reduce yields by more than 30 per cent in the U.S., but above-ground symptoms are not always obvious, which can hinder critical early detection.

Most crop species are imported from other parts of the world and it’s typical for their tormentors to follow.

Since its North American debut on the coast of North Carolina in 1954, SCN has moved through Minnesota and the Dakotas. Now it’s poking its head over the border into southern Manitoba.

The nematode is “among the most damaging of plant parasitic nematodes,” Tylka said. “Its name alludes to the fact that its primary host is soybean, but it also can feed on edible beans of various types.”

[RELATED] Tracing roots for a strategy against soybean cyst nematode

Nematodes are sometimes called roundworms. It’s not clear how many species there are but thousands have been counted to date. Diverse in habitats and tastes, quite a few feed on plants and several find common Canadian crop species to their liking.

“There’s a couple of different ones that like potatoes,” Tylka said. “One is called the pale cyst nematode and another one is called the golden cyst nematode. There are cyst nematodes on carrot and sugar beet and a bunch of different things.”

Their biology can make them serious pests. SCN lives in the soil where it cuts its way into the plant’s root tissue.

“The little worm gets inside the root and injects something into the vascular tissue of the plant,” Tylka said. “This actually changes the biology of those plant cells and they start producing food for the nematode. It’s fascinating.”

That means the plant is using some of its energy to make a custom meal for the worm rather than growing its own tissue or filling pods. One invading nematode won’t dent bean production, but a big enough infestation can seriously weaken plants.

It doesn’t stop there, either.

The name “cyst nematode” reveals something about how it spreads. Males and females invade the root and set up feeding sites. The female grows large and, although its head remains in the root, its body erupts into the soil.

The males, having eaten their fill, move out of the root and mate with the females. Some eggs are then dropped into the soil in a gelatinous sack, but most are kept within the female’s body.

“When she dies, her body wall becomes very tough and leathery to protect those eggs and that’s what’s called a cyst,” Tylka said.

That cyst female is about the size of a period and contains 200 to 250 eggs.

It takes about 22 days to evolve from root invasion to egg production, so there’s a chance for several generations per season.

Eggs that don’t hatch immediately can remain viable in the cyst for several years. If they are in the topsoil, wind can spread them to nearby fields. The ability of the eggs to endure and travel makes them a serious problem.

“It’s a wonderful survival mechanism to have a large proportion of your population not become vulnerable while it’s reproducing all at once in the short term,” Tylka said.

In some cases, soil moisture seems to stimulate hatching. Some need to sense root exudate, the “juice” from a soybean root, so they know a host is nearby.

“Then there’s a third type of egg that doesn’t hatch no matter what we do in an experiment,” Tylka said. “There’s those three hatching behaviours, probably all occurring in one set of eggs in one dead female or cyst.”

That doesn’t mean they never hatch, the researcher cautioned. It just means the trigger isn’t known.

Allowing dormant eggs to hunker down for the long haul can explain why the ancestors of current crop pests were successful. In a wild ecosystem, an annual host plant would be a relative rarity.

Rotate, rotate, rotate

A tight rotation provides the perfect environment for nematodes to reproduce.

“Field research has shown that you can get up to a 50 percent drop in SCN numbers in one year of corn, which roughly means that 50 percent of the eggs hatched out and died off,” Tylka said.

SCN is estimated to cost about $1.5 billion in losses every year in North America, sparking a wealth of management research in hard-hit areas of the U.S.

“Most good ideas and even some cockamamie ideas have been thoroughly explored and it’s just a tough critter,” Tylka said. “Mother Nature came up with a good one when she developed cyst nematodes, so the management is resistance (and) rotating to non-host crops.”

There are seed treatments on the market, the researcher said, but actual control is hit or miss.

The post SCN: The new tough guy on the block appeared first on Manitoba Co-operator.

Soybean cyst nematode (SCN) has been a tough problem since it first appeared in North America back in the 1950s. It’s a soil-bound pest so it can’t be sprayed.

Instead, the solution must be found through biology—finding a weak spot to use to farmers’ advantage.

Unfortunately, according to University of Iowa plant pathologist Greg Tylka, “there’s been researchers working on it for 50 years.”

If there was an easy chink in the armour, it would have already been found. However, there are still a few possibilities.

Every organism has predators and soybean cyst nematode is no exception. In the soil, it’s preyed upon by strains of fungi, mites and other nematodes. Some have been tried as a form of biological control, although none have been successful.

So far, the best solution is variety resistance, and that starts with serious detective work. The ancestral soybean has been dealing with the soybean cyst nematode for a few million years, so plant breeders have gone back to the source to see how the proto soybean did it.

It turns out that those plants had a cheat code that let them win a few rounds against the nematode.

The game goes like this:

The nematode enters the plant and, once inside the root, inserts a sharp tooth called a stylet into the surrounding cells. The worm then injects a cocktail of hormones and signals the plant to feed it.

Plants with a certain genetic combination are able to detect the damage and play an ingenious defence. They cut the damaged cells from their vascular tissue so they starve, die off and form a tough barrier that isolates the nematode from living plant tissue. The nematode starves and dies.

Soybean breeders found two distinct sets of genetic resistance. Both may be available in seed catalogues, but only one dominates the soybean farmer’s roster.

“Almost every soybean variety ever produced to be grown in Iowa, resistant to SCN, has the same set of genetics for resistance,” Tylka said. “It’s a line called PI 88788.”

Now the nematodes are starting to win a few hands. SCN across Iowa has started to achieve higher reproduction on PI 88788.

The other form of resistance is called Peking and, since it’s rarely used, it’s become the more effective form. The problem with Peking is that the plants with that line are less productive.

The race is on to find another source of resistance that offers the efficacy of Peking and the productive capacity of PI88788.

It’s a cautionary tale for Canada, Tylka concluded.

“Don’t be happy to have one set of resistance genetics available for your farmers. Keep working to develop that second one because that first one will eventually wear out.”

The post Tracing roots for a strategy against soybean cyst nematode appeared first on Manitoba Co-operator.

There are two ways a farmer can deal with soybean cyst nematode, according to Iowa State University plant pathologist Greg Tylka.

“The first thing is don’t grow soybeans — but my soybean association asked me to rephrase it as growing non-host crops,” he said, speaking to the Manitoba Agronomists’ Conference earlier this winter.

“The main management strategy is cyst-resistant soybeans. By switching the seed that you plant you can go from stunted yellow beans that yield poorly to very vigorous tall green soybeans.”

Manitoba farmers can rotate to a number of non-host crops such as barley, oats and corn as well as the stalwarts, wheat and canola. Potatoes are also on the non-host list and, like the nematodes themselves, they favour the sandier soils. The nematode likes edible beans though, so if you have a problem with SCN, you might not want to put these crops in the rotation.

“In fact some edible beans are better hosts for soybean cyst nematode than soybeans and there’s research that shows, not surprisingly, SCN would decrease the yields of those edible beans,” Tylka said. “And then with the green peas, it’s a really weird plant, some varieties are good hosts and others are not, so you’d have to be careful with peas.”

The deep, dark problem is that the eggs — and SCN females lay a lot of them — don’t all hatch the next year. Many of the eggs will wait a year or two before they release a juvenile worm so there is a gradual decrease but it’s deceptive. Tylka explained why by looking at a rotation away from soybean to a repeated corn on corn on corn.

“Forty to 50 per cent of the eggs are dormant and they’re not going to hatch out that first year or even a second year,” he said. “It’s the non-dormant eggs hatching out in first-year corn, in second-year corn and by the time you get to third-year corn there’s hardly anything left in the soil except for dormant eggs. Those are going to slowly hatch out over a period of many years.”

Those dormant eggs will lie in the soil for years waiting for the next soybean crop. The best management strategy for dealing with SCN is genetic resistance, the ability of the plant to keep the pest from feeding on it. The nematode lives in the soil and feeds on the root and this hurts the plant and hampers its production so a plant that prevents this kind of damage is a more productive plant.

“The definition of a resistant soybean is a variety that allows less than 10 per cent reproduction compared to a susceptible variety,” Tylka said. “In a greenhouse study, if a susceptible plant supported 200 females per root a resistant plant would support 20 females or less.”

So if the females can’t feed, they can’t reproduce and resistance causes a drastic reduction in SCN reproduction. The trick is to find soybean strains that are resistant to invasion from the nematodes and there are quite a number of them, most of them from Asia. Tylka says that there are seven main sources of resistant genetics but the two principle strains are Peking and the numerical PI 88788.

“Make no mistake though, even though these are soybeans, they are horrific when it comes to agronomics,” he said. “No one in their right mind would grow pure Peking or pure 88788, but soybean breeders take these and cross them with good agronomic varieties and then select for offspring that maintain those good agronomics and have these SCN-resistance genes.”

So this is good news and Tylka talks about the number of resistant strains of soybean he’s seen produced over the years. In 1991 he made a list of resistant varieties that filled about one sheet of paper. Now that list fills a booklet 24 pages long.

Unfortunately, most of the genetics come from those two early sources, Peking and PI 88788 — and it’s starting to break down.

“Unfortunately, for my state, and for much of the upper United States, the varieties that are available only have resistance from these two sources. Ninety-five per cent of our varieties have 88788 resistance and about five per cent have Peking resistance,” he said. “The rhetorical question would be: Is there any reason this won’t happen in Canada eventually? Albert Tenuta and I think Tom Welacky in Ontario have data to show that nematodes in Ontario are building up the ability to reproduce on 88788.”

While the Peking genetics still provide high resistance, Tylka has watched PI 88788 strain resistance drop significantly since the 1990s. He’s conducted field studies over several seasons and found increasing levels of SCN reproduction in fields of 88788 soybeans. One trial in 2001 showed that 28 per cent of the nematode females were able to reproduce, a significant increase from the acceptable 10 per cent and this is causing yield losses in a vital Midwestern crop. Would it be a good idea to move toward Peking resistance?

“We would never want farmers to switch completely to Peking,” Tylka explains. “Peking is working better because we’ve exhausted the effectiveness of 88788. Mother Nature finds a way to overcome that so we’ll eventually lose the effectiveness of Peking. We want to mix 88788 and Peking resistance moving forward.”

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In mid-July, Mario Tenuta of the University of Manitoba confirmed that SCN had been identified in a field in the R.M. of Thompson, an area that had not previously reported the presence of the troubling pest. 

The finding comes after the farmer and agronomist became concerned with yellowed and stunted plants on the headlands of one field, Tenuta said. 

Upon investigation, roots showed signs of cysts, while molecular DNA testing later confirmed that the issue was SCN. 

“They were actually very full of cysts — a lot of cysts. I was quite shocked, actually,” Tenuta said. 

Why it matters: While experts have warned producers that the province’s honeymoon period on SCN will one day draw to a close, it is the first time that above-ground symptoms of SCN have been noted 

The presence of SCN in and of itself is not a surprise. Well-established in the U.S., soybean agronomists have long warned that the yield-eating roundworm, which targets soybean roots, would eventually find its way north to Manitoba.

Tenuta’s work has, thus far, provided much of the basis for tracking SCN in the province. From 2012 to 2019, his team conducted several rounds of surveying, including a survey of 106 fields with a history of soybeans in 18 municipalities in central Manitoba and the Red River Valley. 

Tenuta’s efforts found four fields with SCN, largely along the Canada-U.S border in the municipalities of Rhineland, Emerson-Franklin and Montcalm, although one positive field in the R.M. of Norfolk Treherne, far removed from the others, suggested the possibility that there might be unsurveyed fields infected in other regions. 

In all of those cases, however, nematode levels were low, and there were no above-ground symptoms. 

Tests found two cysts, one cyst and two cases of 14 cysts per five pounds of soil, something that researchers noted was a far cry from regions where SCN has been a longstanding problem. Fields in Ontario and heavily infected parts of the U.S., for example, might instead see 3,000 to 4,000 cysts in the same amount of soil. 

This time, Tenuta said, populations were higher. 

Tests found 32 cysts and 1,350 eggs per 100 millilitres of soil. 

“That’s a decent amount of presence of the nematodes,” Tenuta said, noting that the field had only five years of soybean history, and one of edible beans. 

SCN is among the most infamous soybean pests in the United States, causing an estimated US$1.5 billion worth of yield loss a year. According to the Manitoba Pulse and Soybean Growers, SCN can be linked to up to 30 per cent yield loss by the time above-ground symptoms appear. 

But for all that reported damage, it’s not the easiest issue to identify without digging and lab tests. 

Also known for its mimic of other issues, SCN infection may appear as drought stress, as stunted or chlorotic plants or as poor nutrition. 

One sign, according to Laura Schmidt, agronomist with the Manitoba Pulse and Soybean Growers (MPSG), might be apparent iron deficiency chlorosis that plants never grow out of. 

Below the soil surface, however, farmers will be able to see the cysts themselves. While fragile — agronomists will tell the farmer to carefully dig and rinse roots when scouting — infected plants will develop whitish and lemon-shaped cysts, too small to be root nodules. 

Schmidt noted that dry conditions this year have presented more chance for symptoms to appear, particularly in sandier soils. 

“That’s kind of what the case was here,” she said of the newly discovered SCN case. 

Tenuta noted that the nematode tends to exacerbate drought stress, making sandy soils in dry years prime candidates for first showing symptoms. 

The MPSG is using the recent confirmation to increase aware- ness of the pest and encourage producers to investigate poor stands, which might otherwise simply be dismissed as drought or heat stress. 

Growers can also test for SCN on their own through Agvise if they encounter suspicious symptoms, Schmidt noted. 

Management

Much like clubroot in canola, SCN is a difficult pest to halt once spread has begun. Any movement of soil will also spread the nematode, while management practices such as thoroughly washing equipment between fields is both a nuisance and logistical challenge for producers. 

Washing equipment between fields on the same farm may well not be feasible, Schmidt said. At the same time, however, producers may well want to think of that kind of biosecurity when equipment moves in between farms, or when any new piece of equipment is brought in. In particular, she said, it should be on a farmer’s radar if equipment is coming up from the U.S. or any other area where SCN is established. 

Early detection will also inform the producer of any fields where they should take particular caution not to move dirt, she added. 

Agronomists have also tagged practices like weed control to avoid pest bridges by eliminating host weed species, crop rotation and the integration of resistant varieties for SCN control. 

Producers “should certainly be keeping an eye out and looking for the warning signs,” Schmidt said. “So far, we don’t have high population levels.” 

The key for SCN management, she said, is early detection and preventative action. 

“There are quite a few other host crops and host weeds that it can reproduce on, so if we can catch these fields when cyst levels are relatively low, we know that we need to target those specific weeds when they are cropping up in the field and we also know what we can do rotationally to kind of manage it before those cyst levels explode,” she said. 

Next steps

With a new area testing positive, Tenuta says it may be worthwhile to survey again. 

Work in regards to the confirmed case in the R.M. of Thompson will now turn to genetic screening. Those tests will help determine which resistance genes will be effective against local SCN populations, Tenuta said. 

In addition, his team will be working to determine SCN distribution within the field itself. 

“It it’s in one spot of the field, then that means that it hasn’t spread,” he said. “If it’s in more areas of the field, but maybe in lower levels, some year in the future it’s going to be a problem in the whole field, and they’ll see a yield hit… we’ve got a lot of just fundamental work to do.”

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Soybean cyst nematode (SCN) is a microscopic roundworm that attacks the roots of soybean and is the No. 1 soybean pest in North America. John Wilson, extension educator at the University of Nebraska-Lincoln, says the microscopic roundworm attacks the roots of the soybean plants and can negatively affect yields with no apparent symptoms visible on soybean plants in the field.

SCN was confirmed in fields in four Manitoba municipalities in 2019, and is an endemic problem in most U.S. states. It’s not something that farmers can realistically hope to get rid of once they have confirmed SCN infestations in their fields, but there are things they can do to try and limit its spread and keep population numbers in check.

Speaking late last year at the Manitoba Agronomists Conference in Winnipeg, Wilson emphasized that SCN can be present in one field and not in another that’s right across the road and it’s not an indication of poor management.

Although it’s not possible to visibly distinguish between infested and non-infested plants in the field, there are signs to look for that could indicate that SCN is present. They include unexpected yield losses (up to 40 per cent in some cases) in a perfectly healthy-looking field. Or farmers may have low yield areas on yield maps that can’t be explained because of factors that might normally reduce yields, like herbicide drift, weed pressure, pest or disease issues, compaction or soil type. Over time, soybean yields in a particular field may hit a plateau or start to drop off but when farmers plant other crops in the field, yields are not affected or can still increase.

Another sign to look for is a sudden increase in the presence of SDS (soybean sudden death syndrome) or BSR (brown stem rot) in the field.

“We can have either of these diseases and no SCN or we can have SCN in a field and neither of these diseases, however, if we have a field or portions of a field where SCN concentrations are high, we are more likely to see those diseases,” said Wilson. “That’s because the (SCN) juveniles attack the root and create microscopic wounds where these soil-borne diseases can enter the plant. I have pulled a soil sample from an area of a field with SDS and then pulled a sample 100 ft. over where the soybeans look fine and it’s not uncommon for both of those to come back positive for SCN. When we look at the egg counts in the area where we have the SDS, those SCN egg counts may be up to 10 times higher than in the area where we don’t have those diseases present.”

SCN life cycle

SCN has a life cycle that repeats itself every 25 to 30 days throughout the growing season, depending on the soil temperature.

The only stage of the SCN life cycle that is visible without a microscope is the tiny, white cysts on the plant roots that begin the cycle.

“If we look at them under a hand lens we see they are round or oval, they may be pointed at one or both ends, and on some of them you may notice a kind of gelatinous mass outside of the cyst that contains eggs which are ready to hatch right away if the cyst ruptures,” says Wilson.

If the cyst remains intact, the eggs inside can remain dormant but viable for 25 years or more, and as each cyst can contain up to 400 eggs, it’s an incredibly persistent pest whose population numbers can increase rapidly.

The eggs hatch into a microscopic roundworm that feeds on the developing soybean roots. They excrete an enzyme which causes a breakdown of the cell walls so they can pull more nutrients from the plant. Once the male worms mature, they migrate out of the root and travel up and down it looking for a receptive female, and mate. The female then dies, but her body cavity continues to fill up with eggs until it ruptures through the root wall and forms the cyst structures that start the cycle all over again.

Managing SCN

Managing SCN is about managing the number of eggs that are produced or that emerge. There are three key steps to managing SCN: identification, rotation and sanitation.

Identification is the most important because SCN is so hard to detect that farmers must determine if it is present in a field before they can begin to manage it. There are two ways to identify SCN.

The first is to try and visibly identify the cysts on the plant roots. This can only be done about a month after the soybean plants emerge because it takes that long for them to get through the first life cycle of the season and develop cysts.

“When you are out scouting the field, dig up (not pull) a few plants because if you pull them, you are likely to knock them off the roots,” said Wilson. “If you see cysts you can say yes, you have SCN in the field but if you don’t find any cysts, I would never say you don’t have SCN in the field because it’s too easy to miss, especially at low counts. The cysts might be hard to find because you could be in the wrong area of the field, and it’s not reliable because you won’t have any measure of the density of eggs in the soil.”

A more reliable method of identifying SCN is soil tests. Soil tests can be done at any time of year, but after harvest is probably best and easiest. “Not only are you more likely to detect SCN with a soil sample, you will also have a baseline level that in future you can measure against to see if your management efforts are effective or not,” said Wilson.

Where to soil sample?

Anything that moves dirt, moves SCN, so it’s a good idea to take a core or two at field entries, along fencelines (especially if using tillage that could cause soil to blow and be deposited in these areas), or in high-traffic areas. Farmers should also take samples along creeks or flooded areas or low areas of the field where water pools and can increase the concentration of SCN eggs. Areas with unexplained poor yields, or with SDS or BSR should also be sampled. Because SCN can be highly variable across the field, it’s important to take samples from different areas of the field.

It’s best to take 15 to 25 cores per sample at a depth of six to eight inches deep and to try and sample through the plant roots. Farmers can randomly sample the whole field or sample problem areas separately, taking samples from non-problem areas as well for comparison.

Sampling can be done at any time, but Wilson suggests it may be a good idea to ask the agronomist or field scout who is out scouting or pulling fertilizer soil samples for next year’s fertilizer recommendations to take some additional samples to test for SCN.

In fall, after harvest is a typical time to do these samples, but SCN is easier to detect if there hasn’t been any tillage done, and it’s important to sample right under the crop row to penetrate the root system. Sampling after any crop that soybean is going to follow the next year can give farmers an idea of whether they should choose a resistant soybean variety.

Testing should be done again after six years whether the field is infested or not. “If the field is not infested, and you test again in six years, you will probably still be able to catch it when numbers are low and it’s still easier to manage,” said Wilson. “If you sample and it’s positive and you know the egg count, six years later it’s important to sample again at the same time of year and following the same crop because levels will vary throughout growing season and vary if it follows a different crop.”

If the farmer hasn’t grown the same crop in year six, he or she should wait another year or two until they have and then sample for SCN again. In Manitoba, soil samples can be sent to Dr. Mario Tenuta at the University of Manitoba or AgVise Laboratories to test for SCN.

Rotation

Rotating with other non-host crops can help reduce and maintain low egg numbers in the soil. Normally, anything that farmers grow in Manitoba is not a host for SCN including sorghum, small grains, corn, alfalfa, and most legumes. Dry edible beans, though, are a host for SCN, as are some weeds like stinkweed, common chickweed, shepherd’s purse, wild mustards, henbit and purslane.

The biggest reduction in SCN occurs the first year following soybean and declines more slowly in subsequent years, so the longer the rotation, the better it is to reduce SCN numbers.

It’s also important to rotate the sources of genetic resistance in the resistant varieties farmers grow. Most seed companies offer some choices and the 2020 Manitoba seed guide lists 24 out of 68 varieties that offer SCN resistance, but it may be necessary to find out the source of the resistance from the seed dealer.

There are a number of sources of SCN resistance, and the most common one – PI 88788, which is found in 98 per cent of resistant varieties commercially available is very good but is starting to show signs of breaking down, which is why rotating the source of resistance is crucial.

Research is showing that the populations of SCN reproducing on PI 88788 varieties have started to increase over the last few years, although not as much as they would on a susceptible variety.

Other sources include Peking (PI 548402) and Hartwig (PI 437654), both of which offer excellent resistance, but Hartwig does have some yield-limiting characteristics.

Sanitation

Cleaning equipment before moving it between fields is important to keep SCN out of non-infested fields but farmers aren’t likely to want to stop to pressure wash their equipment halfway through seeding or harvest. Wilson advises that farmers do all field operations – seeding, planting, tilling and harvesting in infested fields last.

Many of the weedy hosts for SCN grow as winter annuals, so it’s vital to control them as a priority in fall or early spring. “Since winter annuals emerge and grow before soybean, controlling them could reduce one generation of SCN during the growing season,” said Wilson.

Research at the University of Nebraska compared the effect of using resistant and susceptible varieties on 29 SCN-infested fields in a corn/soybean rotation, and although the effect on yield wasn’t consistent, the effect on SCN reproduction was. At all 29 sites, sampled in spring and fall, there was an 18 per cent reduction in egg numbers where they had planted resistant varieties, while fields that had susceptible varieties had almost a 300 per cent increase in SCN populations.

“Once you have SCN in a field, we do not recommend planting a susceptible variety in there at all,” said Wilson.

The post Soybean cyst nematode: Managing the ‘silent yield robber’ appeared first on Manitoba Co-operator.

The University of Manitoba, led by Mario Tenuta, has been on the watch for SCN in Manitoba since 2012, but this is the first year that actual symptoms have been reported.

Why it matters: Producers may want to add SCN into their variety choice next year, but most resistant varieties rely on the same genetic source, and evidence out of the U.S. says its days might be numbered.

Last month, Tenuta’s team confirmed both visible symptoms and the microscopic presence of SCN in four fields out of 106 tested this year. Cases were in separate municipalities, although Tenuta later noted that all but one was close to a waterway, exactly the type of area he had been expecting it to crop up since being confirmed upstream in North Dakota.

In response, producer groups and the province urged growers to take a second look at production practices, particularly those that would move soil from field to field. Farmers were urged to reduce tillage, consider wind and weather if they had to till, clean equipment between fields and to minimize traffic.

Resistance, however, was also part of the puzzle. Farmers were urged to consider resistant varieties when planning their seed for next year.

“When you’re planning your rotations, you need to look at how many times you’ve had soybeans and what your risk level is for potentially seeing SCN in the future,” Manitoba Agriculture pulse specialist Dennis Lange said.

Short rotations are at greater risk, he said, along with areas prone to flooding since the pest can spread through water.

There are resistant varieties aplenty, and across maturity groups, according to the 2019 edition of Seed Manitoba. Western soybean trials planted 20 varieties and eastern trials planted 33, according to the document. Some varieties appeared in both the western and eastern trials.

Most resistant varieties on the market, however, are based around the PI 88788 genetic line, genetics that now garner significant resistance concerns south of the border. A monitoring program out of Iowa State University first found an SCN population that reproduced more than 10 per cent on a resistant variety back in 2001. By 2015, every data point tested crossed that threshold. According to the SCN Coalition, a group of American researchers dedicated to SCN research and education, states from Minnesota south to Tennessee can expect anywhere from 17 to 100 per cent of SCN populations to reproduce above 10 per cent when tested on a PI 88788 variety.

In Ontario, that number sits at 33 per cent, according to the coalition.

Cassandra Tkachuk, production specialist with the Manitoba Pulse and Soybean Growers, estimated that about 97 per cent of the resistant varieties in Manitoba rely on the same source of resistance.

“We might be OK here but, kind of like other pests that have moved up spreading throughout the continent, we might be inheriting those resistant pests as well,” she said.

The pest is serious, Tkachuk acknowledged, but it is not serious in Manitoba yet at the levels currently reported.

Confirmed cases this year were not serious enough to cause economic damage.

“Maybe we want to start incorporating these resistant varieties into a rotation, but I would not discredit the varieties that don’t have resistance at this time,” Tkachuk said. “We’re still telling farmers, if you’ve got a really good solid variety that performs on your farm, this isn’t a reason to drop that one like a hot potato.”

Time will tell how well posted resistance translates to Manitoba, Lange said.

There have been improvements to SCN varieties in terms of yield, he added. Farmers who turned to resistant varieties when SCN was first confirmed in Ontario saw a yield hit, he said, something that is not necessarily the case today.

“When you really start looking at the data closely and start looking at comparing it to the check while you’re staying within your maturity grouping, you’re not going to see a huge fluctuation in yields by going to something with SCN resistance,” he said.

Both Lange and Tkachuk urged producers to consider management as a first line of defence.

Seed companies are trying to up their game on SCN.

Articles on company websites, such as Syngenta, note the continuing search for new sources of resistance, including the use of GMO.

The search for SCN resistance was among the topics highlighted at a recent BASF event in Raleigh, N.C.

The company has previously said it is working on resistant varieties, as well as seed treatment options.

“Cyst nematode has a lot of concern just with the resistance in the market today,” Allen Gent, head of BASF’s U.S. soybean business said. “To sustain that with what’s on the market is probably not viable, so we need to make sure that we bring in multiple solutions to kind of give growers an answer.”

The post Look past genetics for soybean cyst nematode management appeared first on Manitoba Co-operator.

Farmers got the unfortunate, but not unexpected, news that soybean cyst nematode (SCN) infections have been confirmed in four municipalities Sept. 16. The nematode, which can spread through water, has been present in North Dakota for years and has been expected to spread north through the Red River. This year, however, is the first that researchers noted both symptoms and molecular test confirmation of SCN.

Mario Tenuta, a soil scientist from the University of Manitoba, led the research project that confirmed its presence. He said the pest has likely been in the soil for “a few years” quietly reproducing and multiplying each season soybeans were grown on the fields.

“Every time that soybean is grown, and the pest is there, it will reproduce and increase its numbers by the production of these cysts, and each cyst contains eggs, many eggs, it could be 200 eggs within a cyst,” Tenuta said.

Soybean cyst nematode is the latest, but not only, soil-based issue that farmers are facing. Similar management techniques apply to most of these pests.

Tenuta’s team has been on the watch for the pest since 2012.

The municipalities of Norfolk-Treherne, Rhineland, Emerson-Franklin and Montcalm have all come down with visual symptoms of the pest, although a recent update from Manitoba Agriculture says none of the symptoms are bad enough to cause economic damage.

One field in each of those municipalities has tested positive. A total 106 fields in 18 municipalities were tested through the monitoring program.

With the exception of the municipality of Montcalm, the nematode has cropped up alongside waterways, exactly where Tenuta and his team would have expected to first see signs of SCN.

“Given the large gap between regions with positive identification, there is a possibility that SCN may be present in fields that were not included in the survey, or may have established since sampling of a field has occurred,” the Manitoba Pulse and Soybean Growers said in a release.

Lessons from clubroot?

SCN management echoes what canola growers have already heard, especially in the eight municipalities with confirmed clubroot symptoms or high spore loads.

That disease has been another source of soil-based anxiety for farmers. The swollen root galls caused by the pathogen threaten to starve plants by cutting them off from nutrients and has caused serious issues in heavily infected areas in Alberta.

Earlier this month, Manitoba Agriculture confirmed a new type of clubroot able to break through some resistant varieties of canola in central Manitoba.

“A lot of the practices that we recommend for clubroot or even for some animal pathogens and viruses, anything that can be transferred in soil or survive in soil, we recommend (biosecurity practices),” Tenuta said.

Both SCN and clubroot can last for years in the soil, leading to calls for longer rotations to curb soil populations and to control other weeds that might act as a host — and therefore a bridge — for either pest.

“The greater the time period between successive canola crops, the better,” Manitoba Agriculture canola specialist Dane Froese told Glacier FarmMedia this July. “Lengthening the rotation really helps the spore load decrease in canola fields, as well as reducing the risk for future infection.”

SCN management follows the same rationale. Tenuta also urged producers to consider resistant varieties the next time it comes time to buy seed, echoing canola-focused advice on clubroot.

Cleaning up

Farmers in the middle of the 2019 harvest, however, may be more concerned with clean equipment.

Experts like Tenuta and the Canola Council of Canada are asking farmers to avoid moving soil from one field to another to avoid spreading an infection. Among other suggestions, farmers are being urged to reduce tillage, give more attention to wind conditions if high-disturbance tillage is needed, and to clean equipment in between fields.

That last may be a hard sell for farmers in the crunch of harvest, Tenuta acknowledged.

“They’re in a pinch. They have a lot of territory to cover and to go back to a yard and wash down their implements may be challenging,” he said.

A mobile pressure washer and water tank may go a long way to mitigate that inconvenience, he added.

Tenuta also urged farmers to make sure used equipment is clean and to keep pickups and trucks out of the field. His own team makes a point to park off the field and walk in during their research, always wearing biosecurity booties.

Both clubroot and SCN are more likely to crop up near field entrances where soil from other fields is more likely to fall, both Tenuta and the canola council say. In 2017, an Alberta agronomist with the canola council, Dan Orchard, urged Manitoba farmers to consider a separate exit from the field for that reason.

That may help, Tenuta acknowledged, although he stressed that clean equipment should be the first option to avoid infection spread and that things like a separate exit should be insurance rather than a main strategy.

Future monitoring

Tenuta hopes to see monitoring efforts expand now that the nematode has been confirmed in Manitoba and has, in fact, been found in municipalities already at the edge of their monitoring program. The scientist would like to monitor areas around Beausejour, the northeast, Selkirk and farther west towards Portage la Prairie and even Brandon.

Some of those areas are newer to soybeans than the Red River Valley, he noted, but are now approaching enough history with the crop for SCN loads to grow.

The post Soybean cyst nematode confirmation presents challenge for producers appeared first on Manitoba Co-operator.

Crop surveys by University of Manitoba Ph.D. student Nazanin Ghavami with soil science professor Mario Tenuta and his students have turned up soybean cyst nematode at “extremely low” levels on soybean plant roots in one field in each of four south-central municipalities: Norfolk-Treherne, Rhineland, Emerson-Franklin and Montcalm.

According to Manitoba Pulse and Soybean Growers in a statement Monday, the pest, a microscopic-sized roundworm, was identified by visual and molecular DNA methods in four out of 106 sampled fields across 18 municipalities. Select fields have been sampled and surveyed in Manitoba’s soy-growing regions since 2012.

Tenuta, in a paper released Monday, noted economical levels of crop damage weren’t observed in any of the four fields with the pest. The low levels are consistent with “recent establishment” rather than a long-undetected problem.

Already confirmed in soy-growing areas of Ontario, Quebec, North Dakota and Minnesota, soybean cyst nematode feeds on soybean roots, causing yellowed leaves, stunted plants and yield loss. Once established in a field, it can remain in the soil for many years.

Cysts were found in the four fields in question during the 2017 survey and later confirmed by DNA tests to be those of the soybean cyst nematode, at “extremely low” levels of two, one, 14, and 14 cysts per five pounds of soil.

Positive fields were resampled in May this year and two were confirmed as having cysts, at levels of two and 20 per five pounds of soil. The field with cysts at the higher level, which was planted to soybeans this year, was visited again in August and found to have cysts on roots consistent in appearance with soybean cyst nematode, Tenuta wrote.

To put the Manitoba cases in perspective, cyst levels in areas of Ontario and the U.S. Midwest where the nematode has been present for “many decades” can be as high as 3,000 to 4,000 per five pounds of soil.

That said, given the “large gap” between the host municipalities with positive identification, “there is a possibility that (the nematode) may be present in fields that were not included in the survey, or may have established since sampling of a field has occurred.”

The Manitoba field in question had “no visible disease symptoms indicating damage from the nematode” such as stunting, poor canopy closure or chlorosis, Tenuta wrote.

The pest’s arrival in Manitoba fields can “still be avoided by preventing the spread of soil from one field to another,” MPSG said in its statement.

Furthermore, soybean growers should consider rotating with non-host crops for two to three years — and, in municipalities with positive cases, using resistant soybean varieties.

Populations of soybean cyst nematode can also be “minimized” by rotating growing cover crops, reducing tillage and controlling host weed species, the grower group said. — Glacier FarmMedia Network

The post Soybean cyst nematode confirmed in Manitoba appeared first on Manitoba Co-operator.

Soil scientist Mario Tenuta, of the University of Manitoba, have confirmed it visually and through molecular DNA methods in four fields, out of a total of 106 fields tested, in a study running from 2012-2019.

At this point just four rural municipalities are affected, of the 18 RMs that were sampled. They are Norfolk-Treherne, Rhineland, Emerson-Franklin and Montcalm (see map below).

Given the large gap between regions with positive identification, there is a possibility that SCN may be present in fields that were not included in the survey, or may have established since sampling of a field has occurred, Manitoba Pulse & Soybean Growers said in a media release.

Cyst populations found in these four fields are “extremely low” and consistent with recent establishment of this pest. The arrival of SCN in Manitoba is not surprising, given the northward spread and distribution across North America. Once established, SCN can remain in the soil for many years.

The arrival of SCN in Manitoba fields can still be avoided by preventing the spread of soil from one field to another.

Populations of SCN can be minimized by rotating to non-host crops, growing SCN-resistant soybean varieties, growing cover crops, reducing tillage and controlling host weed species.

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