The cereal disease is just emerging as a problem to pay attention to in Western Canada, but it is well-established in other parts of the world
Plant pathologists in Western Canada are continuing to learn more about bacterial leaf streak (BLS), an emerging cereal leaf disease that can reduce wheat yields by 40 to 50 percent in severely infected fields.
Mike Harding, a research scientist and plant disease expert with Alberta Agriculture, said confirmed cases of the disease are still relatively low across Western Canada.
But based on anecdotal reports, the disease is becoming more common, both in irrigated areas of southern Alberta and in dryland production areas of the eastern Prairies.
The disease is usually observed in conditions of high moisture and humidity.
Early visible symptoms include elongated yellow chlorotic streaks on the leaves of infected plants.
When infection levels are severe, a bacterial ooze can be observed on the surface of diseased leaves. As the disease progresses, the leaf lesions expand and become necrotic.
Eventually, entire leaves will become brown and dry, losing all of their photosynthetic potential.
The disease often occurs in tandem with other fungal diseases, said Harding, who spoke about the disease during an online Seed Talk Series event, hosted by the Saskatchewan Seed Growers Association.
“Lots of times, it’s easy to misdiagnose the problem because it usually doesn’t just occur in isolation,” he said.
“There’s often times other fungal diseases that can sometimes make it challenging to know if bacterial leaf streak is present.”
Harding said BLS is a relatively new concern to cereal crop producers in Western Canada but is well established throughout the world.
“Just about everywhere (in the world) that we grow cereal crops in a big way, this pathogen is present.”
The disease can affect all cultivated cereal crops, as well as cultivated forage grasses, native grasses and grassy weed species.
Although it is most common in wet conditions and irrigated fields, it can also be observed on dryland production, especially near low-lying grassy areas.
Once established, the pathogen can be spread by crop residues, wind-driven rains and possibly on harvested seed from infected fields.
“It likes areas that have moisture available… and it also likes areas that have warm days and cool nights” that are conducive to dew formation, Harding said.
The disease can easily be confused with bacterial leaf blight, but BLS is caused by a different pathogen that is more aggressive and can have a greater negative impact on the plant’s productive potential.
“We’ve heard confirmed reports of yield loss up to 40 percent in the U.S. and Mexico and, anecdotally, we’re hearing in Alberta and Manitoba, similar numbers in the isolated fields that the disease becomes quite problematic,” Harding said.
“Bacterial leaf streak has, in some areas of the Prairies, become a real significant production impediment.”
According to Harding, BLS was first documented in southern Alberta in 2013.
Initially, researchers were not overly concerned by its emergence but the disease has become more common in recent years.
Canadian researchers are beginning to dedicate more time and resources to studying the disease and learning about transmission and control.
Harding believes that the disease will become more common across the West, requiring ongoing research and management.
The bacteria responsible for the disease does not survive well in soil but can live in host plants including perennial weeds and infected cereal crop residues.
Fungicides are ineffective.
In the United States, in-crop bactericides have shown some ability to control the disease. But the need for multiple applications every seven to 10 days makes existing products uneconomical.
Although the disease has been observed more commonly in certain wheat varieties, there is no conclusive evidence to suggest that any particular wheat variety in Canada is more susceptible than others.
In 2020, Harding’s lab conducted a “non-scientific” non-replicated experiment aimed at assessing varietal tolerance.
The pathogen responsible for the disease was isolated and introduced to 12 different wheat varieties in five different wheat classes, as well as one barley variety, CDC Copeland.
“It (the pathogen) was pretty well equally virulent on everything we tested it on,” Harding said.
“Based on this (experiment), we don’t think this is a specific variety issue.”
Disease transmission is also not well understood.
“Whether it’s being spread by storm systems, or it’s just always existed at very low levels in some of our grassy areas, or whether it’s moved around on seed — we think probably all of the above….”
Harding cautioned against jumping to conclusions based on the anecdotal observations and said more research is necessary.
“Because this has been an emerging issue in the United States over the last five years, they’re quite a bit further ahead of us in terms of scientific research,” Harding said.
For now, the best defences against the disease include following a diverse crop rotation, becoming familiar with the disease and its symptoms, scouting fields regularly during the growing season and using clean seed.
Harding said seed testing should be available soon.
“That’s going to be an option that we need in the future. And staying as clean as we can from the start is going to be a really key piece to managing this disease.
“We just don’t have a lot of management options. We’ll use host resistance if it becomes available and we may get some incremental help from seed treatments if they become available but there isn’t anywhere in the world that’s solved the bacterial leaf streak issue with either of these two tools.”
Harding said the disease, while still relatively new to Western Canada, is likely to become more common and will need ongoing management.