Although last year’s brutally hot and dry conditions across much of the Prairies made for very difficult cereal crop production, they carried one upside — disease pressure was notably low in almost all fields. Which diseases steal cereal crops’ yields and compromise their quality this year, and by how much, will depend heavily on weather through the growing season. However, it pays to plan ahead.
Rust risk
Because so little rust existed in-crop last year, overwintering is unlikely. Instead, rust inoculum including leaf, stem and stripe rust will blow in from the south. Inoculum from the Pacific Northwest typically infects south and central Alberta and southwestern Saskatchewan fields, though spores can blow as far north as the Peace region and west-central Saskatchewan. Fields in the central to eastern Prairie region predominantly receive inoculum from the Texas to Nebraska corridor.
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Kelly Turkington, a plant pathologist with Agriculture and Agri-Food Canada in Lacombe, Alta., says reports from both Washington State University and the Texas corridor have mostly predicted low to moderate rust risks, though late March reports indicated both leaf and stripe rust.
“It has been fairly dry, so there has been limited development. The recommendation for Pacific Northwest growers from Dr. Chen at Washington State University is that they may not necessarily need to put a fungicide on at herbicide timing but to keep monitoring crops and follow the rust risk reports in terms of whether the rust starts to develop as the crop moves into flag leaf stage and heading and so on,” says Turkington. “We’ll keep watching those source locations, especially as we move into late April and early May, to give some indication of risk for Prairie producers.”
FHB management
Fusarium head blight (FHB) will likely be a key concern for cereal growers right across the Prairies, both because of its potentially devastating effect on cereal crops and its difficulty to control.
“Having to make the decision to spray before symptoms are evident in the crop can be extremely difficult to do and, quite frankly, can be quite stressful for the producer or crop consultant,” says Turkington.
Staying ahead of FHB depends on a multi-pronged management strategy.
“(Risk maps) can be a good starting point, but shouldn’t be the only tool a farmer uses,” says Ashley Ammeter, an agronomy extension specialist with the Manitoba Crop Alliance.
At the crop planning stage, producers should ensure a minimum two-year rotation between cereal crops, be cautious about planting cereals next to fields that suffered significant FHB infection the previous year, and — at least in high-risk areas — consider planting FHB-resistant varieties. Once the crop is growing, regularly walking your fields to be aware of moisture levels and crop staging is critical.
Bacterial leaf streak threat
Unlike FHB, it’s possible to see the in-crop development of cereal leaf spots and rusts (tan spot and septoria in wheat and scald, net blotch and spot blotch in barley). Plan a fungicide treatment strategy accordingly. Most wheat varieties on the market today have low levels of tan spot resistance, so maintaining a crop rotation with non-cereal crops (or either barley, which is less susceptible, or oats, which is resistant) is very important, says Ammeter.
Arguably the biggest new and notable disease risk for Prairie cereal producers is bacterial leaf streak (BLS), which has shown increasing frequency and severity in the last few years in wheat and, occasionally, barley.
“Producers might think, ‘That’s a southern Saskatchewan under irrigation problem,’ but it can occur anywhere in Alberta, Manitoba or Saskatchewan. We saw some issues in 2020 with a grower in east-central Alberta who, by the way, was not under irrigation,” says Turkington.
In addition to being easy to mistake for a fungal leaf spot disease, BLS is difficult to manage because control options are so limited.
“People looked at antibiotics, they looked at copper-based or other products, but the level of control has been variable and disappointing. There’s really no in-crop application you can put on for it,” he says.
That reality, together with the fact that BLS remains, at least for now, largely seed-borne in the Canadian Prairies, means careful seed selection, together with ongoing scouting, is critical. BLS requires points of entry into the plant, so cycles most easily on a crop that has been compromised by severe weather — scout carefully after thunderstorms, hail, heavy rain or windstorms.
Seedling blights, root rots and other seed and seedling diseases get less attention than above-ground, more visibly symptomatic, diseases. Fields with inconsistent germination may be compromised by Fusarium graminearum or the spot blotch pathogen, which also causes kernel smudge.
Mid- to late season, pull up plants to look for root disease, especially in fields with tight rotations.
Producers should also watch for ergot, which ebbs and flows in infection rates across the Prairies but is most common in copper- and boron-deficient soils, crops stressed at head emergence and/or uneven crop stands, says Turkington.
While predicting crop disease risk is difficult, Ammeter says producers should keep the classic disease triangle in mind: susceptible host, virulent pathogen, favourable environment. Also, looking at fields’ histories could be advantageous.
“One way a producer can try and gauge what issues they may have is to look at past field and disease history as well as any adjacent fields. That gives a good indication of what potentially might be there and what potentially could develop, especially together with the disease resistance rating of the variety you’re looking to grow as well as previous varieties,” says Turkington.
