New root rots slamming Alberta pea growers

Producers across the Prairies are facing devastating losses in their pea crops — and new species of root rots may be to blame

On bad years — those with cool, wet springs; years like this one — Donald Mueller is lucky if his pea fields yield three bushels an acre. He’ll make back his seed and not much else, losing north of $400 an acre in inputs.

Still, the good years have made up for the bad, so for 25 years, Mueller has grown peas.

But no longer. Devastating root rots that wither and kill his crops have forced him to throw in the towel.

And he’s likely to be one of many. Experts say new types of root rots are already having a huge impact on some pea fields across the province, and the problem looks set to become much worse.

For Mueller, who farms near Three Hills, there’s not much choice in the matter.

“It’s beat us up so bad that, for now, we can’t afford to grow them,” he said. “We’ll eliminate them from our rotation until there’s some resolve on this.”

Root rots in peas are characterized by damaged root systems, stem lesions, stunted plant growth, and yellowing.

Root rots in peas are characterized by damaged root systems, stem lesions, stunted plant growth, and yellowing.
photo: Jennifer Blair

Mueller first noticed the problem in his pea fields four or five years ago, when his crops started to become yellow and stunted.

“I did some soil tests and asked some questions, but nobody could shed any light on it.”

In the years since then, he’s been trying different things, such as changing seeding depths and delaying seeding. Seed treatment seemed to help in some fields last year, but had little effect this year.

“Any of the land that’s had peas on it over the last 25 years showed up with this root rot,” he said. “We tried a few other things after they emerged and started showing trouble, but we couldn’t get any traction. Any place that has showed signs of this just gets steadily worse.”

Root rots are “something all of Alberta is struggling with,” said Syama Chatterton, research scientist with Agriculture and Agri-Food Canada.

“It’s definitely something that is present throughout the whole province.”

In the early part of summer, federal and provincial researchers surveyed more than 150 Alberta pea fields to assess the severity of the issue. So far, southern Alberta seems to be faring the best, said Chatterton. On a rating scale of 1 to 7 (where 1 is healthy and 7 is dead), southern Alberta pea fields had a disease severity of about 2.5 — a level below the threshold where yield loss might occur.

But the incidence of disease is “still pretty high.”

“Seventy-five per cent of the fields you go into have some incidence of root rot, but when you actually look at the roots, there’s only about 50 per cent of the roots that are showing rot.”

Eastern Alberta pea crops have been hit the hardest.

“We found about 20 per cent of roots that were pulled out had a rating of 7. That means that the plants are dead,” said Chatterton. “There was only about 30 per cent of roots that looked completely healthy.”

In western Alberta, where Mueller farms, the average severity is around 3, but there was “quite a cluster” of plants with a rating of 5 and 6.

“That’s pretty severe root rot,” said Chatterton. “The plants aren’t dead, but you’re still going to have an effect on yield.”

New pathogen

Getting to the bottom of the root rot problem is “not a simple story,” said Chatterton.

“There’s a lot of different species that are coming out of the roots,” she said. “We need to start off by knowing what is causing the root rot in your fields. We need to know what pathogens are there.”

Fusarium — a soil-borne fungi that attacks the root structure of the plant — is the usual suspect, causing the majority of root rot problems across the Prairies. But in 2012, researchers in Saskatchewan found a new pathogen of root rot, one that has been spreading across pea-growing countries in Europe and parts of the United States.

That same pathogen was found in samples in Alberta in 2013.

“Finding aphanomyces is a pretty big deal,” said Michael Harding, research scientist with Alberta Agriculture and Rural Development. “This is the biggest production impediment to pea growth in North America and around the world.”

Aphanomyces is a “different ball of wax” because of how it attacks the plants, he said.

“The aphanomyces pathogen doesn’t just set up shop in the spring,” said Harding. “It’s going to continue doing that all throughout the season whenever the environmental conditions are conducive to the spore germination.”

And rotation — one of the only tools producers have to fight root rots — may have little effect on this new species. Both fusarium and aphanomyces produce a resting spore that can survive for over a decade, said Harding, and a four-year rotation may not be long enough to reduce the level of disease in the field.

“For many root rots, rotation and rotation alone is a really potent management tool. The levels of those pathogenic organisms decline over time to the point where they aren’t a significant issue,” he said. “But organisms that produce these long-lived resting spores are really troublesome.”

Over the years, disease levels in the soil can continue to build, and if the environmental conditions are conducive to disease, “it becomes catastrophic in some fields.”

“Rotation is the key thing that we do have to continue preaching and practising, but it’s not going to give us the solution that we need for this problem.”

Even so, Harding isn’t advocating for a change to crop rotations just yet.

“I don’t think we’re ready to make any changes to the recommendations,” he said. “I think one in four in many fields — maybe most — is going to be adequate.”

Root rots such as fusarium can also attack cereal crops and other legumes, but in most cases, rotating to a cereal or even another pulse crop will still provide an advantage — a result of the pathogens adapting to individual hosts.

“They’re very specialized on that one host, and if you rotate to a different host crop, it does give you an advantage because now the population has to reshuffle its genetics,” he said. “Even though some of these fungi that are in the soil have a broad host range, rotation is still a very important piece of management. Unfortunately, it doesn’t get us all the way to control.”

Resistance far off

With limited control measures available for root rots (see accompanying article), Chatterton is working to develop a risk assessment tool that will allow producers to screen for root rot pathogens in their fields.

“I can’t tell you in four years whether you can put peas on your field again,” she said. “But if you could submit a soil sample where we could do that analysis, then we’d feel more comfortable in saying yes, you can probably grow peas.”

Next year, researchers will also be looking at root rot resistance in local pea varieties, said Chatterton.

“In the U.S., they do have resistant germplasm, and now that we know that it’s present in Saskatchewan, breeders there are working on moving that resistance in,” she said.

But new resistant varieties are a ways off yet.

“They’re pretty close to finding the molecular trigger so they know what to look for in resistant varieties, so that will really help speed up the process,” she said. “But it still will be a number of years before they can get it into a variety that producers will want to grow.”

This is becoming “a critical issue for Alberta pea production,” said Harding.

“We need the best root rot tolerance we can get,” he said. “There is germplasm out there that has root rot tolerance in it, and it can be moved into commercially relevant varieties that have the agronomics that you need to make money growing peas.

“There’s hope on the horizon that this can happen, but unfortunately, it doesn’t happen overnight.”

About the author

Reporter

Jennifer Blair

Jennifer Blair is a Red Deer-based reporter with a post-secondary education in professional writing and nearly 10 years of experience in corporate communications, policy development, and journalism. She's spent half of her career telling stories about an industry she loves for an audience she admires--the farmers who work every day to build a better agriculture industry in Alberta.

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