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World’s Worst Soybean Disease Hasn’t Arrived Here Yet

Soybean cyst nematode is the worst of the lot when it comes to crop diseases that thrive in soybean crops.

It infects the roots of soybean and eventually becomes a cyst. It can cause a variety of symptoms including chlorosis of the laves and stems, root necrosis, loss in seed yield and general suppression of root and shoot growth. It can also reduce yields by as much as 75 per cent; it’s estimated that it costs growers in the U.S. as much as US$500 million annually.

Scary numbers, but not something that should be causing Manitoba soybean growers to lay awake at night fretting, according to one expert in soybean diseases.

Allan Xue, a research scientist with Agriculture and Agri- Food Canada (AAFC) at the Ottawa-area Eastern Cereal and Oilseeds Research Centre, says there just hasn’t been any sign of it yet in this growing region.

“This is very, very good,” Xue told the Manitoba Special Crops Symposium during a presentation Feb. 9. “It’s the major disease in soybean production around the world.”


It can be found throughout the corn-soy belt of the U.S., the major soy production regions of Latin America and even up into Ontario.

So why has Manitoba gotten a pass thus far? In part because the province is a new region and in part because the harsh climate keeps pests in check, Xue suspects, along with the fact that growers in the region are using shorter-season varieties that may be a bit more resistant.

“I think it’s really a combination of both being a new area and the colder weather,” Xue told theCo-operatorfollowing his presentation.

And whi le growers can breathe a bit of a sigh of relief for now, Xue says he’s not offering any rock-solid guarantees that they won’t be in battle with the pest in the coming years.

“We will need to be watching closely for it,” he said.

And in the meantime, there are still plenty of other challenges to go around, including various types of soybean root rots, mainly caused by four main disease sources, which include a fungus, a water mould and other types of pathogens including pythium, phytophthora sojae, rhizoctonia solani, and fusarium.


The severity of these diseases can vary a fair bit from year to year and location to location, but Xue stresses that an epidemic year can seriously limit production, and that there’s an

economic case to be made for controlling these diseases.

“A bad year can mean a 30 per cent loss of production,” Xue said.

Of the four main diseases that Manitoba soybean growers struggle with, phytophthora root rot is clearly the most destructive, as it can attack the plants at almost any stage of development. Infection symptoms can include seed rot, pre-and post-emergent damping off in early season and stem rot later in the season.

There’s also the difficult wrinkle that this particular disease comes with a large number of different “races,” while resistant cultivars only have resistance against certain subtypes, making appropriate variety selection crucial.

“Of course that’s easier said than done,” Xue said. “Growers won’t necessarily know what races are present in their fields.”


However, he says he’s generally found that the most popular varieties in a given growing region tend to have the right resistance, because those that don’t won’t perform as well. He recommends selecting resistant or partially resistant cultivars and combining that protection with high rates of chemical seed treatment containing the active ingredient metalaxyl.

The other three common disease sources are even more challenging, with no varietal resistance available to combat them. Seed treatment is the only viable option. But when it comes time to select seed treatment options, Xue said it’s important to get that selection right too.

“Not all of the available seed treatments can control all four diseases,” Xue said. “Make sure you choose one that does.”

In all cases Xue says planting healthy and disease-free seed is a fundamental starting block, as is a robust crop rotation and good soil drainage.


Notalloftheavailableseedtreatments cancontrolallfourdiseases,make sureyouchooseonethatdoes.”


About the author


Gord Gilmour

Gord Gilmour is Editor of the Manitoba Co-operator.

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