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Crop diseases take a bit of a break in 2015

Drier conditions this past season kept a lid on most crop diseases — but this is probably just a brief respite until environmental conditions line up again

The bad news is that dry weather cut yields across much of the Prairies in 2015. The consolation? This same weather kept fungal diseases in check. In fact, areas that were in the sweet spot of lower pressure but enough rainfall to carry yield were rewarded with exceptional crop quality.

Country Guide recently spoke to provincial plant pathologists about what they saw this past summer, and what it might mean for the future.


In the Keystone province, provincial plant pathologists Vikram Bisht and Pratisara Bajracharya report that growers enjoyed a bit of a break. It’s traditionally the wettest part of the Prairies, especially in the Red River Valley, sometimes referred to as “Death Valley” because of its heavy disease pressure

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This summer, however, while rainfall was mainly adequate to support yields, weather was drier than usual. This translated into lower disease pressure across the board, Bisht said. “Diseases and insects just weren’t a major issue in a lot of cases.”

Bajracharya agreed, saying that in cereals there were some instances of fusarium head blight, leaf rust and stem rust, but nothing that rang the alarm bells.

“They were present, but at fairly low levels,” she said.

Winter wheat was an exception. “This year the timing was ‘good’ for fusarium in winter wheat,” Bisht said. “Flowering seemed to coincide with periods of very high risk, and we saw a few fields that did get caught.”

Bisht said Manitoba growers have come to view fungicide applications on cereals as essential due to the perennially wet and humid conditions, and a few growers even apply fungicides at herbicide timing, flag leaf and flowering stages, for a total of three applications.

“They really like to get good coverage and protection,” Bisht said. “Even when it might not always be the most economical thing to do.”

Bisht also noted that ergot infections in wheat crops had fallen this season, after a fairly serious problem last year.

Corn grower (primarily in the Red River Valley) saw similar results for similar reasons. Drier conditions prevented the usual crop diseases like corn smut, common rust and Goss’s wilt from running rampant. Bajracharya noted Goss’s wilt stayed in check, which was particularly good news for growers who have struggled with it in recent years.

“It’s a bacterial infection, not fungal, so of course fungicides simply don’t work on it,” she said.

Sclerotinia and blackleg were present at low levels in canola, but also not at crisis proportions. So far clubroot, though present, hasn’t become a major issue.

“It was nice to also see the two common diseases of canola were not a major issue for growers this year,” Bajracharya said.

Bisht added this doesn’t mean growers can afford to be less vigilant. Both are stubble-borne infections that can linger in fields from season to season, and robust rotation is a key to keeping both in check, as it is with clubroot, which remains a concern.

“Rotation is a major issue and if it is properly practised it can certainly bring down the risk level for growers for all these canola diseases,” Bisht said.

Soybean honeymoon ending?

Soybean growers didn’t have huge issues this year either — but Bisht said reality is beginning to settle in after a bit of a honeymoon period.

While growers did benefit from the general low disease pressure, they saw some cases of rhizoctonia and fusarium root rot, especially when conditions turned a bit wetter later in the season.

Brown spot, caused by a fungal pathogen, has also begun to show up, and it’s one of those diseases that are typical of soybean-growing areas. When it hits a field it can defoliate plants, but leaves the beans themselves alone, meaning its effect is purely on yield, not quality, Bisht said.

Other relatively minor issues were seen with bacterial blight, though the severity and number of incidents remained relatively low. There was also some minor pressure from pod blight and stem blight, which are caused by a complex of fungal pathogens.

“These are all issues we’re going to have to be on the lookout for in the coming years,” Bisht said. “I’m afraid soybean won’t be quite as much a Cinderella crop anymore.”

Late blight scare

Manitoba’s potato crop continued to fight its ongoing battle with diseases. This year late blight infections appeared in the first week of September, placing growers on high alert, Bisht said.

“It’s a very serious disease, and it can take down an entire crop over the course of just three or four days, under favourable conditions and without fungicide protection,” he said.

One factor in the industry’s favour was an early and relatively dry harvest, which meant much of the crop was already out of danger, Bisht said. This also meant fewer problems with storeability.

Bisht also noted the crop has seen a tricky new insect pest arise recently — the European corn borer. Its presence in potatoes is an unintended consequence of the widespread adoption of Bt corn varieties.

“Potato is its next favourite host,” Bisht said. “This has been seen in other potato production areas in the U.S.”

A Group 4 insecticide will control them, but timing is a real challenge. They can only be controlled while they’re on the plant, but not after they bore into the stem and gain the protection of the plant.

“Timing is going to be a real challenge,” Bisht said.


Moving west, Saskatchewan growers saw much the same pattern, with drier conditions hampering disease development, said provincial plant pathologist Faye Bouchard.

“This was a change after the past several years, where we saw some wetter-than-usual conditions promoting disease development,” Bouchard said.

Bouchard told Guide that plant pathologists typically talk about infections needing a “disease triangle” that consists of having inoculum present, a susceptible host crop and environmental conditions conducive to the development of disease.

“In this case it was the environmental conditions that were the missing piece of the triangle,” she said.

And while drying conditions did affect yields a bit, Bouchard added the emerging consensus is that growers in a lot of areas wound up with much better quality than in recent years, which helped to at least partially cushion the blow.

“There were definitely also a lot less quality issues related to disease showing up in samples during harvest,” Bouchard said. “For example, there were far fewer fusarium-damaged kernels in wheat.”

Growers did apply fungicides when conditions warranted it — i.e. during an elevated risk forecast at flowering. But generally, fungicide use was down in step with the generally drier weather.

“It’s taken longer for (fusarium) to get here, and while growers started using fungicides in the wet conditions, they appear to still be using a decision model that looks at risk levels before they use them,” Bouchard said.

That’s good news because careful stewardship means the products will remain effective longer and won’t fall prey to fungicide resistance.

“A plant pathologist will always say we should protect these products and maintain their effectiveness as long as possible,” Bouchard said. “That means using them only when necessary, and properly rotating between modes of action.”

Low canola disease pressure

The province’s major canola diseases — sclerotinia and blackleg — also seemed to be largely in remission this year, with only a few isolated cases appearing, although it appears there may have been more blackleg when crops were hit with damaging weather like hail, which opened it up to infections.

“That’s our suspicion, and we’re investigating it a bit further to understand exactly what happened there,” Bouchard said.

The perennial advice for growers on canola and diseases is robust rotation, Bouchard said, and it appears the message is getting through.

“We recommend a one-in-four-year canola rotation, and I think there are a lot of growers who are doing a good job of this now,” Bouchard said. “Unfortunately, there are still some areas where rotations are tighter, and when it comes to plant disease, your first and best tool is rotation.”

Yet while growers may have had  lower disease pressure this season, those diseases are still lurking in the background.

“Unfortunately they’re now endemic to the area, and they’ll reappear when we inevitably have more favourable conditions for them in the future,” she said.

The elephant in the room when talking about crop diseases with Alberta producers is, of course, clubroot.

The elephant in the room when talking about crop diseases with Alberta producers is, of course, clubroot.
photo: Supplied


“Crop diseases just weren’t the top-of-mind story this season — that was the drought,” said Michael Harding, an Alberta Agriculture plant pathologist based in Brooks. “That was the issue limiting potential yield this year.”

Dry weather also hampered the development of most of the common diseases in the province, including sclerotinia and blackleg in canola and fusarium head blight in cereals.

“We still saw all the usual suspects,” Harding said. “It’s not like they went anywhere, they were just present at much lower levels.”

When moisture improves, all the common problems will reassert themselves when weather conditions line up, he said.

Unusual suspects

That’s not to say there weren’t a few unusual suspects, however, with a couple of oddities cropping up in Alberta fields that bear watching in future seasons — things Harding said aren’t “ordinary to see or something we’d see every year.”

Wheat streak mosaic, a viral infection commonly carried by the wheat curl mite, popped up on a few wheat fields, for example. There were also cases of aster yellows spread in the same way, this time by the tellingly named aster leafhopper in canola. Neither threatened large acreage, but Harding said growers should be aware that both insects could persist and continue spreading the diseases.

“For example, we’ll see wheat curl mites overwinter on winter wheat, then in the spring move into spring cereal crops when the insects arrive,” Harding said. “These host crops support the disease, but until conditions are just right, it’s not a disease we’re necessarily going to see a lot of.”

Harding also noted that there were more bacterial diseases beginning to crop up, saying he found their development a bit surprising. Two notable examples were bacterial leaf streak in wheat and Goss’s wilt in corn.

A break from stripe rust

Dry weather likely saved growers a tough foe to battle. Stripe rust showed up early in winter wheat fields, only to be greeted by less-than-ideal dry conditions.

“It overwintered on winter wheat and emerged early in the spring, poised to become a major problem — but it never really got rolling,” Harding said.

Stripe rust has been a growing concern in Alberta in recent years. It’s a bacterial infection, so is not affected by fungicides.

Stripe rust has been a growing concern in Alberta in recent years. It’s a bacterial infection, so is not affected by fungicides.
photo: Supplied

It’s a cooler-season disease, so the hot, dry conditions in 2015 didn’t support it, and a number of the commonly grown wheat cultivars in the area also have decent genetic resistance to the disease.

The elephant in the room when talking about crop diseases with an Albertan is, of course, clubroot, a soil-borne disease issue that’s rapidly blown up after being discovered in the Edmonton area just a few years ago. Harding confirmed the disease continues to spread, and that the available genetic resistance isn’t a silver bullet. He talks instead of the need for cultural practices centred around crop rotation and certain cultural practices such as avoiding spreading soil between fields.

With the issue just beginning to appear in the other two Prairie provinces, Harding hoped those jurisdictions can learn from Alberta’s experience and get on top of the situation early, while it’s still relatively easy to control — advice he says also applies on the farm level, due to the way the disease can lurk in the background developing, before appearing as a full-blown wreck.

“This is a disease that is much easier to control if you find it earlier,” he said. “You have a lot more options when you’re dealing with, say, a 30-square-metre patch, rather than 30 or 40 acres.”

Harding said the approach that works best for this disease is really one that’s transferable to any crop issue — an effective rotation, regular and timely scouting including taking the time to know what symptoms to look for, and using tools like economic models and extension information to support decisions.

“That’s the foundation of any good disease-management strategy,” Harding said.

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