Aphanomyces could become the new clubroot

Researcher recommends pea and lentil growers consider a seven-year break between crops

Root rot on peas — severe infestations can cut yields by 70 per cent while aphanomyces spores can linger in the soil for years.

If not managed correctly, aphanomyces could be the next clubroot.

And since longer rotations are the only effective management tool, pulse growers battling the soil-borne pathogen that causes root rot in peas and lentils could be facing a big-time reshuffling of what they grow.

“Our recommendation now is to think about going one in eight (years),” said Syama Chatterton, an Agriculture Canada plant pathologist in Lethbridge.

“We want to see a pulse crop every four years so we recommend you replace peas or lentils with a pulse crop like fababeans or chickpea or soybean.”

But that would be a huge shift, given that peas and lentils account for the vast majority of the pulse acres in the province.

Over the last five years, Alberta farmers have planted anywhere from 1.5 million to 1.9 million acres of peas and generally more than 400,000 acres of lentils. Acreage of chickpeas and fababeans vary but even in a good year are all well below 100,000 acres — and soybeans (which fix nitrogen but aren’t a pulse crop) barely show up in StatsCan’s acreage figures.

But once aphanomyces takes hold in a field, growing peas or lentils can be a nightmare.

“Aphanomyces is a monster that came into our farm and our neighbours’ farms years ago,” Bow Island producer Will Müller said in Alberta Pulse Growers’ recently released 2021 research report.

“Pulse acres have definitely decreased due to this disease and will probably continue to decrease.”

Growers in Will Müller’s area embraced peas in a big way and then a “monster” appeared as fields became infested by aphanomyces. photo: Supplied

Müller, who farms both irrigated and dryland with his brother and father, still remembers how growers in his area embraced pulses in the mid-2000s.

“When pulses came into my area, they took over the dryland area,” he said. “Everyone wanted to grow them, they were the new and exciting crop.”

Many turned to a rotation of wheat and peas, and it didn’t take many years of that before the “monster” showed up.

“We started seeing areas that looked like they were dying or drowned out,” said Müller. “There were sick-looking plants. We didn’t know what was going on, but you dig up the roots, and you could tell — something was wrong. It was not a good scenario to be in.”

The aphanomyces pathogen “destroys the roots from the outside in,” said Chatterton. “In severe infestations in a field, you can try to pull up a plant and all you’ll get is this little tiny strand of root that is left.”

But perhaps even worse is how quickly it can move across a field — which is in sharp contrast to most soil-borne pathogens, which occur in patches and spread slowly.

“Aphanomyces just seems to break all the rules of the classical ideas of soil-borne pathogens,” she said. “It can spread quite rapidly through a field based on soil moisture or flooding.”

And once established, it can take many years for spore loads to decrease to the point where you can safely grow peas or lentils again, added Chatterton, who has conducted extensive research on the disease and has been involved in rotation studies.

“In some locations, we’ve found some recovery after four years, whereas in other locations, we’re pushing six to seven years and we haven’t seen recovery yet,” she said. “It makes our recommendations more challenging.

“It seems it’s really going to be site specific and field specific. Exactly what the conditions are that lead to differences between sites — we don’t know that yet.”

Infestations vary across the province, with hot spots including areas around Three Hills and Peace River and the counties of Starland and Knee Hill.

“And even in southern Alberta where it is much drier, we find it pretty extensively down here as well,” said Chatterton.

Ditto up north.

“It’s been pretty widespread north of (Highway) 16,” said Jerome Isaac, who farms at Crooked Creek east of Grande Prairie. “In northern Alberta, it’s been pretty wet the last few years. A lot of pea growers started seeing some really devastating losses due to these root rots — aphanomyces being the dominant one that spread really rapidly.”

Isaac has seen yields cut in half, although he doesn’t know how much of that was because of root rot caused by aphanomyces and how much was because of wet conditions. But he has seen how quickly spores can infect a field.

“The disease can really propagate and move a lot faster in the soil when it’s wet,” he said. “We’ve seen it spread really quickly across our acres. The biggest thing we’ve started watching a lot more closely is our rotation and the amount of years between crops.”

Isaac has started growing fababeans, which are more tolerant to wet conditions and have a greater resistance against soil-borne diseases.

He’s also seen first hand the benefit of longer rotations after amalgamating two fields. The part of the field that was in a three-year rotation for peas had much lower pea yields than the part that had been in a four-year pea rotation.

“You’re not necessarily going to get the same effect across the board,” he added. “I know some farmers who have still had good crops on three- and four-year rotations. Other people have been devastated on a five-year rotation.

“It’s a hard one to calculate but the length in the rotation sure does seem to help get the disease pressure to lessen.”

Müller noted that he hasn’t seen evidence of aphanomyces on his irrigated land — something he attributes to the fact he has more cropping options for irrigated acres and so hasn’t grown peas as often.

“The rotation on irrigation is not that bad as the dryland. It’s such a dry area that we are kind of limited on what we can grow,” he said.

He is now growing wheat, lentils and mustard in the rotation to mix it up. Lentils are susceptible to aphanomyces, but they don’t seem to get it as badly as peas do.

“On a wet year, you see a bit of it in the area,” said Müller. “You can point out the areas where the root rot is. The prices are still good to grow lentils (so) the incentive is still there to grow it. Everyone still wants to grow it.”

Isaac had been using a rotation of peas, wheat and canola, but has now moved to targeting five years between pea crops.

“I would get an agronomist’s opinion of what that should be. We’re experimenting,” he said.

Both Müller and Isaac are directors with Alberta Pulse Growers and both are strong supporters of funding more research into the pathogen.

A lot has been learned since aphanomyces was first positively confirmed in Alberta in 2013, said Chatterton, but there are a lot of questions that need answering.

And given the widespread hope that pulses will join cereals and canola as pillars of Prairie agriculture, it’s important to find more ways to prevent and manage the pathogen, she said.

“Pulses are such an important part of our crop diversity and sustainable agriculture on the Prairies,” she said. “We don’t want to see pulse acreage start to decrease, especially since the goal of the pulse industry is to have 25 per cent of acreage cropped as pulses.”

About the author


Alexis Kienlen

Alexis Kienlen lives in Edmonton and has been writing for Alberta Farmer since 2008. Originally from Saskatoon, Alexis is also the author of two collections of poetry, a biography, and a novel called "Mad Cow."



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