Root rot rears its ugly head — and there’s no treatment

Peas are the biggest concern and even when fields look OK, root rot can still be there

Pulse acres have increased in Alberta this year, but unfortunately root rot has increased as well.

“We’re hearing and seeing evidence of pretty extreme root rot in pulses, especially peas,” said Mike Harding, research scientist and plant pathologist with Alberta Agriculture and Forestry.

“It doesn’t look like it’s going to be a great year for anyone who has peas in a field that is prone to getting root rot.”

Root rot was first detected two years ago.

“While it has been here for a significantly longer period than that, it has flown under the radar,” said Harding. “It seems like it’s a new pathogen for us but in reality, it has been here for a while. As a result, we haven’t been breeding for resistance, or looked for products that are effective against it.”

Pea roots affected by aphanomyces root rot.

Pea roots affected by aphanomyces root rot.
photo: Mike Harding

The impact on peas depends on how long peas have been in the rotation, compaction, drainage issues, and rainfall amounts. The organisms that cause the disease are soil-borne and can infect the plant at any stage.

“There are all kinds of things that line up and in some situations, it is severe; in some it is moderate; and there are some pea fields out there that look wonderful,” said Harding.

When infected, a plant begins to yellow, as the roots lose the ability to move nutrients up from the soil. Plants can look wilted and sick, and in some cases, might die off.

“For some reason, some varieties seem to stay greener above ground longer than some others,” he said. “The damage is done to the root and the yield loss is still there, but the plants don’t show symptoms as bad as some others. Some varieties look really, really bad when they get root rot and others look not quite so bad.”

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Producers should scout periodically for root rot.

“Even in the absence of above-ground symptoms, you can still look for root rot by digging up the plant and just having a look at the root,” said Harding.

In a normal pea crop, there should be a cluster of pink, healthy, nodules on the roots to fix nitrogen. The roots should have lateral root growth and look like a big ball. But root rot pathogens cause small lateral and feeder roots to die out, so the ball becomes a stick, instead of a nice, robust root system.

The root system can have a honey brown colour with aphanomyces root rot, and black in the case of fusarium root rot.

Pea roots affected by fusarium root rot.

Pea roots affected by fusarium root rot.
photo: Mike Harding

Drainage and rotation

Good drainage can make a huge difference as fields with poor drainage are susceptible to root rot, as are compacted ones. Crop rotation is also key.

“If a farmer has only been growing peas for 10 years and has a four-year rotation, we see fewer issues, because those pathogens haven’t had time to accumulate in the soil,” said Harding. “With farms that have been growing peas for 30 to 35 years, the pathogens may have accumulated above that threshold where we start to see severe problems.”

There is no current treatment for the disease, save for seed treatment before planting.

Producers should avoid planting peas in fields that are waterlogged or have low spots with poor drainage.

“Try to avoid fields that have compaction issues; choose lighter loamier soils rather than hard clay that gets packed and compressed.”

Producers in the irrigation areas should take care not to waterlog their soils.

“Use high-quality, certified seed with a seed treatment. If you have both fusarium or aphanomyces in your field, then you need two seed treatments,” said Harding.

Alberta Pulse Growers recommends producers who see root rot should avoid seeding peas or lentils on that field again for five years. It also has a root rot guide at pulse.ab.ca.

About the author

Reporter

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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