Smut is one of the most common diseases in barley and can be found anywhere the grain is grown. There are several distinct kinds, each caused by a specific fungus and producing slightly different effects.
While smut affects other cereals, it’s particularly a concern for Prairie barley growers because of its impact on quality as well as yield. Barley is the only cereal grain that can be downgraded because of the presence of smut, and tolerances can be low.
According to David Kaminski, a provincial crop pathologist with Manitoba Agriculture, there’s little farmers can do if smut has taken hold in a barley crop, but there are steps they can take to prevent that from happening.
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Kaminski spoke with growers about the seed-borne disease last summer, as he stood before a smut-infected barley plot at the Crop Diagnostic School. Staged annually by Manitoba Agriculture and the University of Manitoba, the event was held in Carman, Man., in July.
Kaminski said the incidence of smut was less than one per cent, but if barley seed from the plot was collected and planted the following year, there’d likely be a tenfold increase in the number of infected plants.
The point he was making was that fungicidal seed treatments are an important aspect of controlling smut in barley crops. The plot had been intentionally sown with untreated seed to demonstrate to farmers what would happen.
“At the diagnostic school, my saying is that we break things so that you don’t have to fix them. We show you what not to do. And in this case, the ‘what not to do’ was to not treat the seed with any kind of a fungicide,” he said.
Kaminski said the plot also illustrated how it doesn’t pay to try to cut corners with bin-run seed. He encourages farmers to find the most advanced or effective form of seed treatment with systemic fungicide, to avoid smut turning up in their barley crops.
During his demonstration, Kaminski noted the infected barley contained three types of smut: true loose smut, covered smut and false loose smut.
The latter two are both surface-borne smuts, meaning spores stay on intact seed coats as the barley plants grow, and may or may not be visible.
As Kaminski noted, these spores aren’t released until toward the end of the growing season, sometimes by the crushing action of the combine during harvest. This is when smut spores will infect healthy grain.
“True loose smut, on the other hand, gets released and infects healthy heads fairly early in the season and actually grows within the seed,” said Kaminski. “So, it’s infecting the embryo, but there is no outward sign that that infection has taken place.”
In infected seed heads, healthy grains will eventually be replaced with clumps of dusty, black spores, which can be spread by wind or rain to healthy plants, where the disease cycle will start once again.
Kaminski showed growers a barley seed head with true loose smut, then flicked it with his finger, dispersing the black spores in a tiny swirl of dust. By the end of the season, he said, all that will be left of an infected seed head will be a bare rachis.
In a phone interview with Grainews in October, Kaminski discussed some other management techniques barley producers can use to prevent smut from spreading in their fields.
One is planting certified, disease-free seed — an obvious choice since smut is spread through infected seed.
Another is to use smut-resistant barley varieties.
“There is a real range of resistance, from susceptible to moderately susceptible to intermediate to moderately resistant to resistant,” said Kaminski, noting farmers can find resistance ratings in provincial seed guides such as Seed Manitoba.
Kaminski said if growers find evidence of true loose smut in their barley, they should check to see how the variety stacks up in terms of disease resistance.
“If there are alternatives…that have better resistance, then I would be switching varieties as another management steps to reduce the incidence of true loose smut,” he added.
Kaminski noted plant pathologists frequently talk about how crop rotation can be a silver bullet for fungal disease, but he stressed that’s not necessarily the case with smuts in barley.
“The reason is there really isn’t a soil-borne phase of any of these smuts,” he said, explaining that the pathogens are either in the plant growing in the field or in seed that’s semi-dormant until it germinates the following year.
“You don’t have to worry about infection that comes from the soil,” said Kaminski. “If you’re starting with certified seed, it’s been treated and it’s a more resistant variety, there’s about a zero chance that you will see infection in that crop.”
