Check Your Soybean Fields for Harmful SCN

By Harry Siemens

Soybean cyst nematode (SCN) is a microscopic roundworm that parasitizes soybean roots.

Researchers have found different nematodes in Manitoba, but not all are harmful to crops. That is not the case with SCN. It is a harmful type of nematode and one of North America’s most damaging pests to soybean crops.

Preventative action, early detection and timely management are key to avoiding significant yield loss from SCN.

The presence of SCN was confirmed for the first time in Mani- toba in 2019. This confirmation was made possible due to survey efforts led by Dr. Mario Tenuta and his research at the University of Manitoba that took place from 2012 to 2019. They identified SCN visually and by molecular DNA methods in four out of 106 fields and four out of 18 municipalities sampled across all surveys.

In July 2021, they confirmed another case of SCN. The arrival and spread of SCN in Manitoba is not surprising, given SCN’s northward movement and distribution.

Laura Schmidt, a production specialist with the Manitoba Pulse & Soybean Growers, covering western Manitoba addressed the SCN problem with growers at St. Jean Farm Days on January 11.

She said it has crept north from the Midwestern United States.

It is a small soil-borne roundworm that infects soybean roots and robs plants of nutrients. It has a big impact on soybean yield depending on environmental conditions, but it’s also creating lesions on roots which cause root rot infection to take hold.

“We see more symptomatic plants under dry years because SCN infected those roots and diminished the root material. So it can take up less water or search for water under drought conditions,” said Schmidt. “And it’s a big yield robber for soybeans.”

For some years industry people were expecting the first shoe to drop and now the honeymoon period for soybean farmers is over.

“With soybeans more regularly in the rotation, some of these pests are starting to creep in and make themselves a little more aware,” said Schmidt.

She said that farmers in western Manitoba are still in that grace period. But in the Red River Valley, there are no more. Many farmers think of soybeans as a crop to plant and then forget about after applying the herbicide.

“It’s one where we need to be digging up roots, looking at how our nodules are developing and whether we see any soil-borne pests—and maybe keeping more of an eye on it instead of seeding it and forgetting it,” she said.

Schmidt said so far there are not too many confirmed cases in Manitoba. The cyst levels were relatively low in the initial round of surveys that discovered it in 2019.

“I don’t think we were ex- pecting to see yield loss with those populations, but they were so low, like the earliest detection possible in the field we found in 2021, we actively saw yield loss,” said Schmidt.

Some patches had aboveground symptoms because it was a dry year, and those roots couldn’t dig up water. But even further into the field where plants looked healthy above ground, they found those cysts on the roots impacting yields.

She said farmers could dig up soybean roots to look for these cysts. If they have six years of soybean history, they can even sign up for a survey that’s going on this year and next year led by Dr. Tenuta and his lab at the University of Manitoba.

“We want to know where this pest is in Manitoba, how high our populations are,” said Schmidt. “Participating in that survey is a great way to determine if it’s in your field because they could use precise detective measurements using their molecular methods to say if it’s there or not definitively.”

With current cluster programs ending in the last federal funding program for research, the goal is to start a new cycle.

“So SCN is one of the pests we want to highlight for soybean management long term in this next round of funding,” said Schmidt. “And we do have some research we’re hoping to move forward with Dr. Tenuta.”

She said surveillance is one of those efforts, but there are also management options that he wants to look at such as SCN-resistant varieties and how they behave with the SCN populations found in Manitoba; also looking at different nematode-protectant SCN treatments, how they work in fields infected with SCN and response.

“We have a lot of resources we can lean on, but it’s also research to determine how its going to behave this far north and in our unique situation.”

Soybean cyst nematode (SCN) is a microscopic roundworm that parasitizes soybean roots. Once SCN has arrived, it spreads rapidly and cannot be completely eradicated. SCN eggs can survive for several years in the soil but requires a host plant to reproduce. Management options include rotating to non-host crops, growing SCN-resistant varieties, reducing tillage and controlling host weed species.