Still no magic bullet for fusarium head blight

There’s still no cure, but at least there’s no sign of fungicide resistance. Yet

As corn acreage expands on the Prairies, there will be a whole new crop that can host fusarium spores.

“We have no magic bullet.”

When Randy Kucher, associate professor at the Crop Development Centre/Department of Plant Sciences at the University of Saskatchewan, said that at the beginning of his presentation, the mood in the roomful of CropSphere attendees deflated just a bit. Fusarium head blight has stolen yield from many durum and spring wheat crops across the Prairies in recent years, and there is still no miracle cure. The only way to control FHB is through integrated pest management practices, including long crop rotations and choosing good genetic varieties.

Even when it comes to varieties, Kucher said, in durum, “moderately susceptible is about as good as it gets.”

The news didn’t get much better from there. As corn acreage expands across the Prairies, Kucher said, there will be a whole new crop that can host fusarium spores.

While fusarium graminearum is “our main culprit,” Kucher said, we are “dealing with multiple diseases that may be slightly different from one another.”

As well, there are two or more forms (chemotypes) of DON (deoxynivalenol) produced by fusarium graminearum. The most common ones are 3ADON and 15ADON. Kucher explained that there is a “relationship between the aggressiveness of the pathogen and these chemotypes.” The 3ADON is becoming more common in Western Canada, as compared to the 15ADON. This change in chemotypes could partially explain why the fusarium graminearum pathogen is becoming more aggressive here in recent years.

Researchers are working overtime to find new sources of genetic resistance to fusarium. They examined more than 10,000 samples and tested their propensity to become infected with fusarium. “Basically,” Kucher said, “we ranked them from one to 10,000.” In the end, they chose the best 400 samples (or “accessions”). “Fifty per cent of them, at least, have low levels of infection in the field,” Kucher said. “We think we’ve got a really good collection now.”

This work is important because currently, most of the moderately-resistant wheat varieties we’re growing have been bred using genetic resistance from Sumai 3, a Chinese spring wheat variety. By examining so many different accessions, researchers are looking to find a brand-new source of genetic resistance to FHB.

You’re not too late, maybe

At that same CropSphere presentation, Gursahib Singh, from the University of Saskatchewan’s Department of Plant Science reported on a recent study of the best timing to spray fungicide on durum. He prefaced his words by reminding everyone that fungicide can be used “to suppress the disease, not to control it.”

Singh reported that, in cases where fungicide can’t be sprayed at the optimal time, durum growers may be able to consider extending that application window to as late as BBCH69 — when all spikelets have completed flowering.

“We’re not recommending people wait until 69,” Kucher said. “Maybe don’t give up if you think it’s a little late.”

Fungicide resistance?

There is a risk of fusarium becoming resistant to the fungicides we’re using to control it. The risks of resistance are especially high when growers are primarily using a single mode of action, when there is a wide diversity of fungi in the population, where there is an abundance of spores, and when there is a frequent application of fungicides.

So far, we are getting off lucky.

Singh said researchers have conducted surveys of the FHB population in Saskatchewan and Manitoba in 2014 and 2017 to measure the growth of the fungus over time. They didn’t find any signs of developing resistance. “Nothing extraordinary, everything was normal,” Singh said.

Although no resistance has been found yet, Singh still recommends that farmers rotate chemicals, use fungicides that include more than one mode of action, and do not overuse the same fungicide group in the same season.

“We’re spraying huge areas,” Kucher pointed out. “We need to start thinking about fungicide resistance because we know it will happen.”

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