Manitoba poised to meet advancing soybean cyst nematode

The pest’s arrival is imminent if it hasn’t happened already

Cysts (the large white growths) on the roots of a soybean plant.

A microscopic parasitic roundworm that’s the top soybean yield robber in the U.S. is already present on the Manitoba-North Dakota border and the province is readying for its imminent arrival.

Soybean cyst nematode (SCN) is often cited for causing approximately US$1 billion in U.S. soy production losses every year, and it’s that kind of devastation Manitoba hopes to avoid, according to a University of Manitoba applied soil ecology professor.

“I don’t think that’s going to happen here because we’re expecting it and looking for it,” says Mario Tenuta, who recently spoke at CropConnect.

Current surveys show SCN hasn’t reached Manitoba, but its presence across the U.S. border implies it soon will be established here. Manitoba is likely to be the first of the Prairie provinces to get hit, and the western expansion of soybean acreage will be followed by SCN establishment.

Past experiences

One of the difficulties in dealing with SCN has been misdiagnosis. When poor yields appeared in affected U.S. fields, SCN wasn’t immediately thought of as the problem. Symptoms are often mistaken for something else, like a rooting problem, compaction or lack of nutrients.

“The nematodes will compromise the root system and the plant then struggles to take up water and nutrients,” says Tenuta. “It takes awhile for the buildup of nematodes to get to levels that are affecting the yield significantly.”

Nevertheless, by the time SCN has been found to be the problem in some cases, the population levels became high enough to cripple yields, he says.

A soybean cyst nematode and its egg, at 1,000x magnification. photo: Creative Commons/USDA/ARS

Manitoba and Prairies

The plan north of the border is to manage SCN before it causes yield reductions.

“Once it gets into fields it’s challenging because it will in effect stay there forever,” Tenuta says. “So what we try to do then is go to a management where we keep the population levels down so that they won’t be high enough to cause field damage.”

One of the most important strategies is for farmers to incorporate a rotation plan that ensures they avoid growing soybeans in back-to-back years. He recommends soybeans once every four years and no more than once every three.

Another management strategy is to seed a resistant variety of soybean. Although it won’t prevent growth of SCN populations, it will slow it down, Tenuta says.

He adds farmers should also try and prevent cross-contamination of soil from one field to another.

Chemically speaking, there are some nematicides that are commercially available, but it’s not entirely clear what efficacy they’d have here or the other two Prairie provinces, or to what degree their use would be warranted.

“They might be useful in the strive to keep the population from growing, together with resistant varieties.”

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