Oat growers may want to gauge the distance to the nearest woody stream bed the next time they choose a variety.
That’s one of the messages sent out during this year’s Crop Diagnostic School in Carman in the first two weeks of July.
Why it matters: Manitoba’s most popular oat varieties have either been downgraded for crown rust resistance or were already moderately susceptible, and woody stream banks contain wild hosts for the pathogen.
David Kaminski, a field crop pathologist with the province, warned that common buckthorn provides an easy wild host for the pathogen. The infected buckthorn plants are a haven for spores to overwinter after they blow in from the United States, he said. Susceptible oat varieties may be in trouble with crown rust if planted within a few miles of those wild areas.
“If you were 15 or 20 miles from any river or stream course in Manitoba, it’s very unlikely that you’ll have a concentrated source of inoculum that moves into your field, but if you’re within a couple of miles from a stream that has woody species along it, there’s a good chance that there are spores available at the time when the crop is also susceptible,” he said.
Two of the pathogen’s five life cycle stages impact oats, he said, while common buckthorn is affected by three.
“The first and second spore stages come out on the leaves of buckthorn (in) early, early spring when our crops are still seedlings,” he said.
Common, or European, buckthorn is endemic along Manitoba’s waterways, Kaminski went on to say. The Invasive Species Council of Manitoba lists the woody shrub as a problem species, both in the province’s natural areas and in green spaces within Winnipeg. It is commonly mistaken for the native chokecherry bush with its dark berries and is highly adaptable to different moisture and light levels, the council says.
The plant’s thorns are a hazard for both people and livestock, the council’s website warns, while the dense shade created by buckthorn stands impact the ability of natural plants to compete.
The Carman research station knows the buckthorn problem all too well, given its proximity to the Boyne River.
Commercial oat plots this year are planted to Souris oats, a variety still advertised for its crown rust resistance, although Seed Manitoba counts the variety as moderately susceptible.
The older Souris variety has fallen out of favour with millers, agronomists attending the diagnostic school said, although about 17 per cent of oat acres in Manitoba were planted to Souris as recently as 2017. The variety’s popularity dropped significantly last year, accounting for only nine per cent of the province’s 401,000 oat acres.
One of the province’s most popular oat varieties shares that crown rust susceptibility, however. CS Camden is also labelled mildly susceptible and accounted for 40 per cent of oat acres last year.
Manitoba’s second most popular oat variety last year, Summit, was also downgraded in 2019 thanks to changes in crown rust virulence in Manitoba. Seed Manitoba counted the variety as resistant until this year, a rating that dropped to intermediate in the publication’s 2019 edition.