OMAFRA crop pathologist says almost undetectable soybean cyst nematodes are across Ontario

By Connor Lynch
A devastating soybean pest has been creeping its way across Ontario for years and a crop pathologist said now is the best time for farmers to get their soil tested.

Soybean cyst nematode (SCN) was once a soybean pest in the United States but over the last 70 years it has crept farther and farther north, hitting the Chatham-area in 1988 and moving steadily eastward since.

Levels of the microscopic, parasitic roundworm have been found as far east as Ottawa and into Quebec, said OMAFRA’s field crop pathologist, Albert Tenuta, who also sits on the board of the SCN Coalition.

One of the difficulties of dealing with the nematode is it’s a stubborn pest with a long lifespan and a slow burn. Populations of nematodes can build in the soil slowly, over five or even 10 years, without farmers being able to see much or any damage to their crop. But once they start dealing physical damage, growers can count on 25 per cent yield loss in the first year.

Without management, areas of the field with the nematodes can hit 60 per cent yield loss within five years, said agronomist Dale Cowan.

The nematode can survive 14 years in the ground without a soybean crop in the field, so rotation isn’t enough to handle it. Once it’s in a field, eradication is basically impossible, Tenuta said.

Tenuta believed the parasite can be anywhere in Ontario but you won’t know until you test. Given how far afield the nematode ranges, and how stealthily, “Whether our surveys have detected SCN or not, it’s almost become a moot point,” he said.

Get a soil test for nematodes, particularly in fields where you’ve just grown soybeans or are planning to next year. Three labs, all in Western Ontario, will do tests: The Pest Diagnostic Clinic at the University of Guelph; SGS Labs at Guelph; and A&L Labs at London. Tenuta added that if farmers have a soybean field that has been lagging in yields for no clear reason, definitely get a test. It’s a classic sign of nematode infestation.

To test for the nematode, take 15-20 one inch samples from eight inches down per 20 acres. Mix, put in a soil sample bag, then send to a lab.

Managing the parasite can include switching to resistant seed varieties, changing rotation and applying nematicides, Tenuta said, adding that he recommends sampling that field again four to six years later. “Are you beating SCN? Or is it beating you?”