Cereal diseases to watch in 2020

Tan spot, septoria complex, scald, FHB and root rots top the list. What’s the outlook for your region?

Agriculture and Agri-Food Canada is predicting a slight increase in seeded acreage of wheat in 2020.

Difficult spring planting conditions ran the gamut across the Prairies in 2019 from limited to excess moisture; however, moisture levels going into 2020 look adequate, with projected cool, dry conditions.

Regardless, producers should start the season armed with a scouting plan for cereal diseases, says Mallorie Lewarne, agronomy extension specialist for Manitoba Wheat and Barley Growers Association.

Leaf spots

In wheat, producers should be on the lookout for leaf spot diseases, primarily tan spot and the septoria complex, which includes speckled leaf blotch and leaf and glume blotch. Although spot blotch can also attack wheat, it is generally less of a concern.

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Kelly Turkington, an AAFC pathology research scientist based in Lacombe, Alta., says diseases of concern will vary depending on the province or region.

Cereal leaf spot diseases typically develop from old, infested crop residues, he says, which means producers with short rotations should be on the alert for these diseases.

In the western Prairie regions where it can be cooler with more rain, barley producers should look out for scald, a rain-splashed pathogen.

Net-form net blotch affects producers across the Prairies, and spot blotch is also increasingly common across those provinces, while spot-form net blotch can also be found, Turkington says.

Lewarne says in Manitoba, the first disease growers should be looking out for this spring should be tan spot, especially if it’s a cool spring and the field has a short wheat rotation.

“It shows up as tan or brown flecks on lower leaves. I would get out there when you’re scouting for weeds, as early as possible,” she says.

Leaf spot diseases are polycyclic, explains Mitchell Japp, provincial cereal crops specialist for Saskatchewan Agriculture, which means pathogens causing these diseases can produce more than one infection per crop cycle.

Producers should be out monitoring as the crop moves toward the flag-leaf stage.

“Protecting those leaves is critical,” says Japp. “In moderate- and low-disease pressure years, if there’s going to be a fungicide application at the head blight timing, it can manage leaf spot, but under high-pressure years you might require two fungicide applications.”

From top left: 1) Glume blotch in wheat; 2) Leaf rust in wheat; 3) Speckled leaf blotch in wheat; 4) Scald immature lesions in barley.
photo: Kelly Turkington

Rusts

Particularly for barley, leaf rust can be an issue, especially in the central to eastern Prairies from mid-June to the beginning of July, says Turkington. Leaf rust typically travels to Western Canada on wind trajectories from wheat in the Texas to Nebraska corridor.

Historically, stripe rust came from the Pacific Northwest, reaching southern Alberta in “half a day,” he says. However, over the last several years, stripe rust of wheat has been an increasing issue in the Texas to Nebraska corridor and the eastern Prairies.

Stripe rust can also overwinter in the Prairies on fall-seeded winter wheat, which means it can start showing up on winter wheat as early as April. “If you have a mild winter with good snow cover and you have a lot of stripe rust on your winter wheat the previous fall, it can survive those fairly mild winters and start developing much earlier than we would normally see,” says Turkington.

Rusts don’t require extremely wet conditions and can develop in a crop under heavy dews.

In Manitoba, Lewarne says compaction stemming from wet harvest conditions is a risk factor for rust.

Fungicide should be applied as soon as stripe rust symptoms are observed and before they cover five per cent of the flag leaf.

Fusarium head blight

Fusarium head blight can cause significant yield loss but chiefly causes concern as a downgrading factor in wheat when the fungus causes fusarium damaged kernels (FDK). In barley, fusarium can cause discolouration and affect malting and brewing quality. In both crops, mycotoxin contamination can also have a significant negative impact.

Fusarium risk maps are available across the Prairie regions. Producers can familiarize themselves with risk factors on each of the provincial agriculture websites, but shouldn’t neglect walking in the field to visually assess the crop and moisture levels, says Japp.

“All cereals, regardless of their resistance rating, are somewhat susceptible, it just depends how much,” says Japp. “Being out in the field and seeing what’s there is really critical.”

In barley, spray timing recommendations typically call for application right after head emergence, but Turkington’s research group is currently looking at later timings. In wheat, too, producers are typically advised to stop spraying once the wheat head has reached half flowering, but new data shows reasonable control up to the end of flowering (BBCH growth stage 69).

“For growers who have a lot of acres to cover, if they’re starting on the front end and get pushed by rain or the number of acres, there is an option where they can go a couple of days later than what’s historically been recommended,” says Japp. “It extends the window a little bit.”

Root rots

Root diseases tend to be overlooked in Western Canada, says Turkington. “Out of sight, out of mind — but they can be an issue,” he says.

Common root rot is an issue in both wheat and barley. The fungus overwinters in crop residue or as spores in the soil and thrives in dry, warm conditions, especially with over-application of nitrogen.

Another root rot that was historically important in the Prairies is take-all root rot, and this disease might regain importance as producers are taking an interest in liming soils to raise pH to address clubroot in canola, says Turkington. As soil pH increases toward neutral, the risk of take-all also increases, he warns.

“It tends to be unusual, but as the name implies, when the fungus infects relatively early in the season due to wet soil conditions, it can destroy most of the root tissue. The tools to manage it are pretty limited, with extended rotations being the main tool, while adequate copper fertilization can lessen its impact.”

For this and the other cereal diseases, Turkington recommends frequent scouting.

“Knowing what’s happening in your field gives you valuable information about whether you need an in-crop application, while also having implications for future crop planning,” he says.


Disease monitoring network

The Prairie Crop Disease Monitoring Network (PCDMN) offers scouting, disease and risk information based on crop development stage in-season. Find them on twitter at @pcdmn.

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Julienne Isaacs

Julienne Isaacs is a Winnipeg-based freelance writer and editor. Contact her at [email protected]

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