MEDICINE HAT, Alta. – Field crops in Western Canada are always under threat of disease. Plant pathologist Ron Howard of Alberta Agriculture categorizes them as internal or external threats.
“The internal threats are those diseases that we already know occur here and that could spread into new areas or develop new strains that could increase their impact and economic importance. They’re out there now, maybe in localized areas in low levels, but given the right conditions they could really take off,” Howard said at a recent Reduced Tillage Conference in Medicine Hat.
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In contrast, he said external threats are diseases not established on the Prairies but could become detrimental to yield and quality of crops and to native plants if they gain a foothold.
Howard highlighted three external cereal disease threats: wheat stem rust, karnal bunt and dwarf bunt.
With oilseeds, internal threats included powdery mildew on flax, stem blight on sunflower and blackleg on canola. One external oilseed threat mentioned was verticillium wilt of canola.
Cereal disease threats
Stem rust
Howard said there’s a new strain of stem rust causing concern worldwide, UG99, which was discovered in Uganda in 1999. This rust was able to attack breeding lines developed out of the cereal and corn breeding centre in Mexico.
“It spread quickly to wheat growing areas of Kenya and Ethiopia. The fear is, it’s going to move up through the Arabian Peninsula, across east Asia and India, and perhaps into China,” said Howard.
“A lot of the common varieties in use in those areas are quite susceptible to this new strain of stem rust. The potential exists for these airborne spores to spread the pathogen long distances with storm fronts. Concern is it may only take a few years before it covers thousands of kilometres as it moves eastward.”
Howard said UG99 is a typical stem rust, causing lesions on heads and stems. And it’s aggressive. A global rust initiative has been formed, focusing solely on UG99.
Canada is part of the initiative, exploring resistance to UG99 in some varieties grown here. The initiative has published a report available on the internet, called Sounding The Alarm On Global Stem Rust.
The report recommends countries with large wheat industries, such as Canada and the United States, take immediate action.
“We have had our wheat lines in east Africa being screened at the field level. It turns out most of them are susceptible to this rust, but there are a few with resistance. Breeders are now looking at back crossing those genes into our present day wheat varieties,” said Howard.
Karnal bunt
Karnal bunt originated in India and can infect wheat, rye and triticale. It reduces wheat quality because of the smut spores, odours and off flavours.
“The infection is favoured by cool, wet weather and it has been reported by the U.S. and Mexico. Southern areas like Arizona and Texas have had some outbreaks and eradication efforts are underway there,” said Howard.
Karnal bunt infects plant florets and has fishy smelling spores. Contaminated grain will adversely affect flour flavour and animals won’t eat it.
While it has never been reported in Canada, Howard said it’s considered a quarantine disease here. It can be seed and soil borne, so there are restrictions for Canadian wheat breeders who want to manage plots in the southern U.S.
He said it’s difficult to control, with a unique life cycle that includes a soil borne phase.
Dwarf bunt
Dwarf bunt is mainly a winter wheat disease, but it can also attack rye, certain grass species and barley. It reduces yield and quality.
Howard said the disease now occurs in two areas of Canada: the Okanagan and Shuswap areas of British Columbia and parts of southern Ontario.
“For many years, the (Canadian Food Inspection Agency) has monitored it so it doesn’t move from B.C. onto the Prairies. Most Canadian winter wheat varieties are susceptible.
“It’s both seed and soil borne. The spores are very allergenic. People’s sensitivity to these spores is much more than other smut and bunt spores,” he said.
“The spores are also very flammable. When there were serious outbreaks of dwarf bunt in the Pacific Northwest back in the early 1900s, hundreds of threshing machines went up in flames because the spores caught fire and burned everything up.”
Oilseed crop threats
Powdery mildew
Howard said farmers and researchers in Manitoba noticed powdery mildew on flax in the early 1990s.
“It’s a form of fungi that parasitize leaves and stems and form a white, powdery growth. This is a new one that is now also found in low levels in Saskatchewan and Alberta,” he said.
“We don’t know if this is going to get worse, but it is getting more widespread and if you’re a flax grower, it’s one to be on the lookout for.”
Stem blights
In sunflowers, Howard said fungi causing leaf and stem lesions have been seen.
While most of the sunflower acreage is in Manitoba, as that acreage expands into the other provinces, sunflower growers should watch for these diseases.
Blackleg
Even though it’s been around quite a while and producers might think it’s under control with seed treatments and current canola varieties, new blackleg strains have evolved.
“With blackleg, our big concern is the creation of new strains. This fungus has a sexual reproductive cycle. That means recombinations are happening and when it does, it might change the disease resistance picture as far as our canola varieties go,” Howard said.
With blackleg, infections start on the cotyledon, eventually spreading up through the rest of the plant. Big cankers appear on the stems and the plants topple over and die.
“Varieties that are now resistant could become susceptible. In recent years there are three new strains designated PG3, PG4 and PGT, isolated from all three prairie provinces, as well as from some U.S. plains states.
These new strains have the potential of displacing the old strains and rendering some of our varieties susceptible,” said Howard.
Verticillium wilt
Howard said verticillium wilt of canola is a disease specific to the brassica family.
“It’s one we don’t think we have here now, but it’s becoming important in some areas in Europe. The fungus infects the canola plants and causes them to wilt and die,” he said.
“It survives in the soil as microsclerotia, which are tiny fungal structures that can survive for long periods of time under unfavourable conditions. It causes premature plant death and cannot be controlled by fungicides, either as a seed treatment or a foliar spray.”
Symptoms include bright yellow leaves with sectors of dying tissues. The infected plants wilt and often the leaves fall off. Farmers can cut the stems open to look for discolouration, which is typical of vascular wilt diseases.
Howard said there is little varietal resistance, so he hopes it doesn’t make its way to North America.
