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Preparing for the end of the soybean honeymoon

In 2017, soybean acres in Manitoba exceeded that of red spring wheat, with more than 2.3 million acres seeded to the crop. That’s almost a 40 per cent increase over the previous record-setting season. When you consider that there are only 9.5 million acres of cropland in the province, the growth of the crop becomes even more impressive. There are many reasons growers are flocking to soybeans, and many have to do with how few threats there are to the crop’s success — so far.

“Soybeans are a fairly user-friendly crop — you put treated seed in the ground, spray for weeds a couple of times and wait for fall to harvest,” says Nathan Klassen, SeedGrowth Specialist with Bayer Canada. “When we first started growing soybeans in Manitoba we had a number of wet seasons in a row, and guys were looking for a crop that could actually manage the wet weather really well, soybeans were that crop. Ten years later we have early, mid and late-maturing varieties, we have better disease resistance along with great support from seed genetics, so farmers just really like growing the crop.”

Soybeans love long, warm summers and have traditionally been best suited to Ontario and Quebec. Improvements in short-season varieties have permitted the crop to spread into Western Canada. In 2011, 95 per cent of soybeans in Manitoba were seeded in the Red River Valley, and improved varieties have allowed the crop to move north and to the western areas of the province. In addition, Manitoba hasn’t had an early, killing frost in more than seven years, which is also encouraging growers to adopt the crop.
While there are many different types of inoculum throughout the soils of Manitoba which cause issues in a variety of crops, so far soybeans have had few serious issues with disease. It can be fairly easily managed, making the cost of growing the crop lower than some other options. But growers are learning that this situation is unlikely to last forever if tight soybean rotations continue.

Rotate crops and varieties

“We are still in the honeymoon phase when it comes to crop management and soybeans, but eventually that will come to an end,” says Cassandra Tkachuk, a production specialist with the Manitoba Pulse and Soybean Growers. “Soybeans are a terrific crop because they fix their own nitrogen and require less nitrogen fertilizer. They also have been shown to reduce greenhouse gas emissions. Weed control with glyphosate is very effective. But we need to be very careful with our crop and product rotation if we want to keep it as an easy crop to grow.”
Soy disease surveys show fusarium, rhizoctonia and pythium are all root rots which affect Manitoba’s soybean crop. Phytophthora root rot is also common, and is unique in that it can affect the crop throughout the season. Signs of the disease generally don’t appear until the crop has been exposed to stress.

“The best defence against phytophthora is variety selection,” says Klassen. “There have been four main races of phytophthora identified in Manitoba to date, races 4,25,28 and 3. When selecting varieties this is a starting point to make sure the genetics you plan to grow have resistance genes built into the variety that control those races. If you start to see signs of the disease, try a variety that has a different race resistance package, there is no one size fits all; farmers will have to find the best fit for their farm.”

Other seedling diseases such as fusarium, rhyzoctonia and pythium can cause stunted growth, poor emergence or damping off. While roots can be examined to help determine the difference between these diseases, the pathogens can only be confirmed through laboratory testing. Once you have determined you have this disease in your crop, this can help with management decisions in the subsequent growing season. Tkachuk says that growers need to gain a better understanding of what’s in their field before choosing resistant varieties and can look to variety guides for details.
While rotation will reduce the inoculum in the soil and variety selection can help protect your seed from day one, Klassen says that seed treatments will help battle disease pressure in the crop.
“EverGol Energy is a wide-spectrum fungicide seed treatment that covers the common diseases in a Manitoba soybean crop,” he says. “An insecticide like Stress Shield can be added to helps with pest pressure from insects such as wireworms, which tend to impact growers in the lighter soil bands.”

Manitoba Pulse and Soybean Growers has developed a soybean seed treatment risk assessment to help farmers and agronomists identify where seed treatments can be most helpful by detailing the factors that can have an influence on fungal pathogens and insect populations. The guide, which is available under ‘production resources’ on the MPGA website, helps growers make seed treatment decisions as part of an integrated pest management approach.

SCN moves on soil

The approach of other soybean disease is keeping Manitoba soybean growers on their toes. Soybean cyst nematode (SCN) is currently the greatest threat to soybean crops in Ontario and some regions in Quebec, as well in North Dakota and Minnesota. Each year annual field surveys are conducted in Manitoba and so far, there have been no confirmed cases in the province. That’s a good thing, because once it is in a field it is impossible to eradicate.

“We are definitely worried about it in this province, and the more soybeans we grow the more likely we are to find it,” says Tkachuk. “We can only manage its arrival to a certain degree, because it travels very easily on soil or through floodwaters. It is so prevalent in the northern U.S. right now that if we have one of our spring flooding events, which are not uncommon in this province, it will likely be here.”

Tkachuk says crop rotation is the number one defence against the disease at this point in order to minimize the presence of a host crop for the disease to spread through. She says that soybean growers are already looking to warmer climates which have experience with the disease for assistance in developing management practices. She points to Brazil, which is using cover crops to help manage the disease.

This shows soybean roots with smaller soybean cyst nematode (SCN) cysts
(red arrows) and larger nitrogen nodules (blue arrows). Photo: University of Nebraska

“We know it spreads on the soil, but does not move much once it is in place, so once we identify it, it will be critical to choose management practices that keep it isolated if possible,” says Klassen. “We are taking a wait-and-see approach to this disease but at the same time we need to be prepared by learning as much as we can about managing it.”
Sudden death syndrome (SDS) can also have a big impact on yield, and rates of SDS have been steadily increasing in Ontario. As the disease spreads through the soil, management of soil movement is critical to slow the progression of the disease into the province. Growers transporting equipment from the U.S. or Ontario need to keep their equipment clean to minimize risk of importing SDS-contaminated soil.

“The Manitoba Pulse and Soybean Growers and Manitoba Agriculture work closely with the University of Manitoba to identify the disease as soon as it hits our borders,” says Tkachuk. “We are surveying in areas where the disease is more likely to take off so we can identify it sooner rather than later and begin to isolate it to slow its spread.”
Seed treatments will help to suppress the levels of the disease but are not a silver bullet and need to be used as part of an integrated pest management system. Nematicides like ILeVO will help control the damage from SCN and protect against SDS.
“Soybeans won’t stay in the honeymoon phase in this province forever, and at some point growers know it will take more management,” says Klassen. “Diseases are always adapting to keep us on our toes and that pressure is only going to increase — that we know. We need to be proactive to stay one step ahead of disease management where we can.”

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