Aphanomyces hurting pea yield for Sask. producer

After repeated aphanomyces problems, Bernie McLean 
is taking a break from growing peas

Bernie McClean usually has a positive outlook on everything. But after three years of dealing with aphanomyces, he’s taking a break from peas.

“It’s just too risky. I can’t afford the risk,” says McClean over a cup of coffee at his farm, which sits between Glaslyn and Medstead in northwestern Saskatchewan.

Up until two weeks ago, McClean was still planning to seed a couple of small fields to peas. But, as seeding time approached, worries about aphanomyces were keeping him up at night. He’s now planning to switch peas out for malt barley, at least this year.

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The decision wasn’t an easy one to make. Peas broke up the cereals and oilseeds in his rotation. He’s invested in a flex-header and roller. The peas also allowed him to manage his seeding and harvest operations well — many of his other crops needed to be seeded earlier and harvested later.

“It’s a cropping alternative that I’ll miss. We need those options,” he says.

Ground zero for aphanomyces

McClean’s farm has been ground zero in the struggle to manage aphanomyces. In 2012, the first confirmed case of aphanomyces in Saskatchewan was in his field.

That summer, one pea field, which had seen the crop several times over the years, started to show signs of the disease. McClean, with the help of his agronomist and a neighbour, pulled plants and sent them to a Regina lab. Aphanomyces is notoriously tough to diagnose, as other root diseases such as fusarium quickly move in after the initial infection.

They had caught the infection early enough for the lab to detect aphanomyces, but they couldn’t save the crop. He watched his plants wilt and yellow. The root disease destroyed nodules. Most of the acres on that field were a wreck, but one patch that hadn’t seen peas before yielded well.

In contrast, another of McClean’s pea fields that year averaged 67 bushels per acre, winning him the Prince of Peas title with Cavalier Agrow. The high-yielding green peas had been seeded into oats stubble. That was the first year peas had been seeded into that field.

McClean tried peas again in 2013 and the pulses yielded around 65 bushels per acre. By now, McClean felt like he was starting to figure out how to manage aphanomyces. While McClean had known moisture was an important factor, he knew that rotation and compaction also contribute. McClean thought he could manage the disease by picking the right fields.

Water is king

But 2014 proved that when it comes to aphanomyces severity, water is king.

Last year he seeded two fields to peas. One field had seen peas recently, but had only grown peas once before 2014. Historically he’d always seeded into cereal stubble, but this field was canola stubble. He controlled his volunteers. McClean thought it would be a “perfect field.”

But a summer thunderstorm left standing water on that field for a day and a half, derailing the peas. Discovery Seed Labs in Saskatoon confirmed aphanomyces in the field.

“And it devastated that field,” he says. McClean netted 11 bushels per acre from the water-logged field.

Water didn’t pool on the second pea field, which was about a quarter of a mile away. It yielded just over 50 bushels per acre, McClean says.

Peas don’t like wet feet to start with and aphanomyces thrives in soggy soil. Aphanomyces spores have flagella that allow them to swim very short distances through wet soil, infecting roots.

McClean does have land that hasn’t seen peas, but it’s very wet, so he doesn’t want to take a chance. His whole area has been caught in a wet cycle for the last several years. That superfluous water has even killed willows on McClean’s farm. “We’ve lost a lot of acres to water,” he says.

McClean says he can’t see taking a chance on peas until we’re in a drying trend. But now that the disease has built up, he’s wondering if it will affect his crops even in dry years. The disease, which also hits lentils, can survive in the soil for up to 20 years without a host.

Farmers worried about aphanomyces should take it seriously, he says.

“Believe what they’re saying and do your due diligence to baby that field as well as you can if you do want to try peas again,” he says.

Right now farmers don’t have any chemicals or resistant varieties to give them an edge with aphanomyces. Extra moisture seems to the biggest factor, so McClean suggests farmers seed their highest, best-drained land to peas.

Compaction also contributes. McClean had originally planned to seed his peas later this spring, to give the soil time to dry out. He suggests farmers avoid rolling if they don’t have to, or try to roll when the soil is dryer, to reduce compaction.

“Ultimately the goal is to keep the plant as healthy as you can,” says McClean.

Learn online

Although aphanomyces spores are long-lived, longer rotations seem to reduce disease severity. Peas and lentils should only be grown once every four years. And if fields are infested with aphanomyces, rotations should be stretched to six years or more, according to a joint presentation by the Saskatchewan Pulse Growers, Saskatchewan Agriculture and the Crop Development Centre.

While seed treatments don’t prevent aphanomyces, they do fight other, secondary diseases such as fusarium. Farmers should test seed for germ, quality and seed levels, according to the presentation.

If soils have less than 15 pounds per acre of nitrogen, farmers should use starter nitrogen, the presentation states. Phosphorus is suggested when seeding into cold soils. Proper inoculation is a must.

To view the presentation on aphanomyces, visit the Saskatchewan Pulse Growers website.

About the author

Field Editor

Lisa Guenther

Lisa Guenther is field editor for Grainews based at Livelong, Sask. You can follow her on Twitter @LtoG.



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