The rains came and crop disease pathogens couldn’t be happier

Scouting regularly and intensely gives you the best chance of hitting the ideal fungicide window

Premature bleaching of wheat spikelet infected by fusarium head blight, 
which is expected to be more common this year.
Reading Time: 4 minutes

Early season diseases generally passed crop growers by during the dry spring, but rainfall across much of the province means they need to keep a close watch now.

Kelly Turkington. photo: File

“The dry conditions earlier this spring tended to slow things down, but we’ve had moisture occurring, and that has elevated the risk for diseases,” federal research scientist Kelly Turkington said in a July 12 interview.

“If areas have had moisture over the last three weeks, that could certainly start to trigger some of these diseases.”

Two years of dry conditions have largely kept crop diseases at bay, but they’re starting to show up now, said Turkington.

“They might start to see symptoms as the crop progressed past the flag leaf emergence stage into head emergence,” he said.

In cereals, some of the leaf spotting diseases have been cropping up, particularly in the Lacombe area.

“Temperature can be a factor, and moderate temperatures like we’ve had — daily highs of 15 to 30 degrees — coupled with rainfall or heavy dew can be a risk factor,” he said.

Producers should be scouting their crops regularly if they start to see disease developing, he added.

“Do you see symptoms developing in the middle part of the canopy and threatening the inner canopy? If the crop hasn’t progressed a lot, a fungicide application could potentially be useful to limit the impact of leaf spotting diseases.”

Cereal rust is less of a risk, though.

“The risk levels overall based on what was happening in the States were low, so we haven’t seen a lot of rust in commercial fields,” said Turkington.

“Up until recently, there had been no reports, and I’m not sure if they’re starting to see some symptom development. It hasn’t been a big problem, but that’s not to say it won’t be an issue for some later seeded crops.”

Fusarium risk

Fusarium head blight could also cause some problems this year. Back-to-back dry years saw the disease reduce in severity and spread, but the risk is moderate to high in much of the province.

The provincial fusarium risk map can tell you what the risk level is in your area, said Turkington. “Those are excellent tools to indicate where the weather conditions are conducive to head blight.”

Producers should also consider a field’s disease history.

“The more frequently they’ve found it, the more likely the pathogen is established there, and if the weather conditions are conducive to it, a fungicide application may be useful to provide some suppression.”

It’s the same story with root and stem diseases, he added.

Farmers have seen higher levels of ascochyta root rot in pea crops and cereal root rots in cereals, as well as sclerotinia stem rot and clubroot in canola.

“If you have crops that were late seeded, you may have disease development occurring, and you should monitor those crops as they come into flag leaf emergence through head emergence,” said Turkington.

“If the crop is just before anthesis or at anthesis, you could still have significant disease development occurring, especially if it’s a susceptible variety or you’ve got a tighter rotation and we continue to see some moisture occurring over the next two to three weeks.

“If that’s the case, there would be sufficient development of disease that could result in yield losses that might be in that five to 10 per cent range.”

Fungicide timing

The first step to mitigating that loss is scouting your fields, said Turkington.

“Getting out into the field to look at what’s happening is important,” he said.

“For the diseases where you can see symptoms in the field, you can scout your fields, and if they are starting to move in, depending on the pre-harvest interval and the level of disease in the crop, there may be some value in spraying a fungicide.”

If it looks like you’ll need to spray, consider your control options. Older products might be just as effective as newer ones, but at a lower price tag. Or if there are products that have a range of recommended rates, sticking to the lower end of the recommended rate could help you cut your input costs while still offering effective control.

“I’m not advocating off-label application or reduced rates, but if there’s a risk developing, it might only be a moderate risk, so you could still get a reasonable level of control and your input costs are lower.”

But timing a fungicide application correctly will be critical at this point of the growing season, especially in fields where the crop is at different growth stages.

“That’s a real challenge in managing disease in those fields — when do I put that fungicide on?” said Turkington.

“By the time the later germinating plants get to a point where they can be sprayed, the part of the field that germinated earlier may have problems with the pre-harvest interval for the fungicides you’re using.

“Where you’ve got variable development in the field, it’s going to be really difficult to mitigate that, so the recommendation I would offer for that is look at what growth stage the majority of the field is at and then target it to that growth stage.”

But pay attention to your pre-harvest intervals, he cautioned.

“You may be running into a situation where you run the risk of not having an adequate pre-harvest interval and losing market access for your crops.”

About the author


Jennifer Blair

Jennifer Blair is a Red Deer-based reporter with a post-secondary education in professional writing and nearly 10 years of experience in corporate communications, policy development, and journalism. She's spent half of her career telling stories about an industry she loves for an audience she admires--the farmers who work every day to build a better agriculture industry in Alberta.



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