Is climate change making leaf diseases worse?

Durum quality took a beating last year, and climate change could see more of the same

It is difficult — even impossible — to define the precise relationship between climate change and disease incidence and severity in Western Canada.

But new research from Agriculture and Agri-Food Canada’s Swift Current Research and Development Centre is contributing a few pieces to the puzzle.

Research scientist Myriam Fernandez says breeding for resistance to the leaf spot (LS) complex hasn’t made the strides seen in fusarium or other wheat disease breeding programs. But LS is the most frequently encountered disease of bread and durum wheat on the Prairies, and can sharply reduce yield and quality under the right conditions.

Fernandez is the author of a new long-term study assessing the impacts of climate change as well as regional and agronomic practices on leaf spotting in bread and durum wheat.

“It is expected that seasonal fluctuations in the severity of diseases and prevalent pathogens will continue in Western Canada, with the potential for high levels of diseases such as LS and a corresponding decrease in crop productivity,” she writes in the study.

The study looks at data from long-term surveys of wheat and durum acres across Saskatchewan from 2001 to 2012, when the province saw variable weather conditions, including dry years and years with above-average moisture, mostly between 2010 and 2012.

Durum more susceptible

“Disease severity increased going northward and eastward, so it was favoured in wetter areas. This was mostly associated to the septoria leaf complex, which is favoured by wet conditions,” says Fernandez.

The study found that durum is more susceptible to LS than common wheat.

The leaf spot complex (tan spot, septoria leaf blotch complex and spot blotch) is one of the most prevalent and widespread wheat diseases in Western Canada. AAFC says that trials in southern Saskatchewan estimated a 16 per cent reduction of leaf spot disease corresponded to a 17 per cent durum yield increase at Swift Current, while a six per cent leaf spot reduction corresponded to a yield increase of 27 per cent at Indian Head.
photo: Saskatchewan Agriculture

Spot blotch, caused by the pathogen Cochliobolus sativus, showed a marked increase in wetter years, and was most prevalent in durum.

“If wet and warm weather continues, this pathogen could become an important leaf spotting pathogen in Saskatchewan, especially in durum wheat,” says Fernandez. The same trends, she notes, have been described in other parts of the world during similar weather conditions. “It’s very important to also consider that C. sativus also causes root rot and black point/smudge in cereals.”

Linking climate and leaf diseases

Herb Cutforth, an agricultural meteorologist at Swift Current, says climate data in southwest Saskatchewan shows warming over the past 50 years or so, especially between January and April. From May through August minimum temperatures have warmed slightly.

“Yearly precipitation totals haven’t changed much, but the number of events with little precipitation have increased,” he says.

Brian Amiro, a University of Manitoba soil scientist specializing in agricultural meteorology, says that although descriptions of climate trends tend to be very regional, some general western Canadian trends over the last 60 years have shown an uptick in winter temperatures and less snow; this means some pathogens could more successfully overwinter across the region.

Climate studies, as distinct from weather, look at longer-term patterns, and it is difficult to pick out specific climate-related signals influencing diseases, says Amiro.

Nevertheless, it seems clear climate change will have an impact on Canadian crop production into the future, says Amiro, who was an editor on a 2014 Alberta Institute of Agrologists green paper into the need to adapt production practices in response to likely climate scenarios over the next few decades.

The green paper cites International Panel on Climate Change (IPCC) projections that suggest the prairie region will see a one degree Celsius increase in summer temperatures and a two degree Celsius increase by 2050, as well as the potential for a 10 to 20 per cent increase in precipitation.

Best management practices

The Saskatchewan study showed that for bread wheat, leaf spot severity was greater after a year of summerfallow under reduced tillage than when wheat had been preceded by an oilseed crop under reduced tillage. For durum wheat, LS severity was greatest for reduced tillage systems where there was no previous crop information followed by summerfallow systems. In contrast, durum wheat with a previous oilseed crop had the lowest mean disease severity.

Fernandez says her recommendations for curbing disease pressure have remained the same since the 1990s, and will become even more important if disease pressure increases.

“Use the most resistant cultivar available,” she says. “Do not practise summerfallow, and diversify crop rotations with non-cereals, such as pulses, as much as possible, particularly when using zero-till.”

“Only use an aerial fungicide if spotting on the upper leaves is significant, and don’t apply a fungicide at early crop growth,” she adds. “All wheat crops develop leaf spot lesions on the lower leaves which, depending on the environment later on, and the susceptibility of the cultivar, might not progress much further.”

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