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Manage root rot before seeding

Saskatchewan plant disease specialist recommends good agronomy to reduce root rot

Lentil and pea growers struggling with root rot need to manage the disease before the seed is in the ground, according to Saskatchewan Agriculture’s plant disease specialist.

Fusarium, pythium, and rhizoctonia are root rot pathogens long familiar to farmers. But aphanomyces is a relatively new problem, only detected in Saskatchewan in 2012.

“It probably was widespread and present before,” Faye Dokken-Bouchard told farmers at Canadian Western Agribition’s Grain Expo. But without the excess moisture, the pathogen didn’t cause disease symptoms in the field until Saskatchewan had years of excess moisture, she added.

And the disease isn’t going anywhere. Aphanomyces spores can survive for a long time in the soil. Excess moisture in the future will put infested fields at risk again, Dokken-Bouchard told farmers.

Identifying the rot

Stunting, yellowing plants are above-ground symptoms of root rot. Poor root growth, poor nodulation, and rotting roots are also signs of pathogens.

“But it’s also important to note that excess moisture can often cause these types of symptoms on its own. And then if you add a combination of wet feet along with diseases, then you’re going to have an even bigger issue,” said Dokken-Bouchard.

Farmers wondering whether they’re facing aphanomyces or fusarium should take a close look at the roots. Caramel-coloured roots indicate aphanomyces, said Dokken-Bouchard. Pink or red-tinged roots mean farmers are likely seeing fusarium.

The Alberta Pulse Growers suggests gathering field information to diagnose root rot in peas and lentils. That information includes rotation history, herbicide history, moisture situation in recent years, soil information and seeding information. Farmers should also look for patterns such as misses, overlaps and compacted areas.

The group also suggests creating a map marking good and bad areas, topography, patterns around disease symptoms, heavier soils, water runs and side hill seeps. Aerial photos can also help.

Finally, the pulse growers recommend collecting soil and plant samples from good and bad areas, and sending them to a lab for analysis. Options include BDS Laboratories, Discovery Seed Labs, and 20/20 Seed Labs.

Management options

Asked whether tillage could help manage disease, Dokken-Bouchard said it depends on the crop and the pathogen. Some research has shown tillage helps because it breaks down residue faster, or buries the spores.

“But then on the other hand, it might bring some inoculum back up to the surface and make it more accessible,” said Dokken-Bouchard. And losing the benefits of reduced tillage might not justify any potential reduction in inoculum, she added.

“It’s not really yes or no. It’s kind of maybe.”

Dokken-Bouchard recommended farmers test seed for disease and germination. Depending on the disease level and type, farmers may not want to use the seed at all. Seed treatments are available for root rot pathogens such as aphanomyces, rhizoctonia, fusarium and pythium.

“But you have to keep in mind that with all of these diseases, they might be in the crop residue or in the soil as well. So even if you have low levels of disease on your seed, you could still have disease issues,” said Dokken-Bouchard.

Crop rotation is “critically important” to managing disease, said Dokken-Bouchard. Fields with aphanomyces should see a six-year break from peas, lentils, and other hosts. Other susceptible crops include alfalfa, dry beans, and some red clover varieties. Chickpeas and fababeans are generally less susceptible to aphanomyces.

Field selection is also an important way to manage aphanomyces. Dokken-Bouchard advised farmers to consider previous issues, moisture levels, differences in soil, and compaction. Waterlogged soil and compaction favour the disease. Heavily textured soil is more likely to suffer from waterlogging and compaction.

Asked whether farmers can soil test for root rot pathogens, Dokken-Bouchard said labs such as Discovery Seed Labs do those tests. But interpreting those levels is tricky right now, she said.

Good agronomy, including weed control and fertility, also help bolster the crop against root rot. Alberta Pulse Growers suggests considering starter N in soils that have less than 15 pounds per acre in the top 12 inches.

Phosphorus is a good idea if seeding into cool soils early in the season. Assuming adequate moisture and narrow openers, maximum safe rates of seed-applied P for lentils are 25 lbs./ac., and 20 lbs./ac. for peas, states the Alberta Pulse Growers’ factsheet.

Such practices help the crop get off to a good start “so that it’s not going to be stressed out and more susceptible to all kinds of disease issues,” Dokken-Bouchard said.

About the author

Field Editor

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

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