The value of validation
Monitoring the unpredictability of wheat midge populations
When Dr. Tyler Wist joined Agriculture and Agri-Food Canada (AAFC) as a field crop entomologist in 2016, there wasn’t a coordinated effort for monitoring wheat midge across the prairies. So as a new research scientist, one of his key roles was to protect the integrity of the wheat midge tolerance gene (Sm1) that’s available to wheat growers in Western Canada.
Researchers have been working on wheat midge in Canada since the 1990s when populations of the insect pest were out of control. The widespread availability of midge tolerant wheat has provided a solid agronomic tool against the midge and an estimated 35 per cent of wheat planted in Western Canada is midge tolerant. And yet, Wist is discovering how much there is still to learn about wheat midge to control its impact on wheat crop yields and quality.
Following up on forecasts
Every year, Alberta and Saskatchewan produce provincial midge forecasting maps to provide insight for growers before they make seed purchases in the spring. The maps are built on midge cocoon populations gathered from soil core samples in close to 300 field locations across each province. Manitoba doesn’t produce an annual forecasting map.
Midge cocoons are counted and populations are mapped and colour coded from green (low risk) to red (high risk) for their potential for damaging midge emergence the next spring.
In 2021, Wist began coordinating Midge Busters – a collaborative field project with SeCan to distribute pheromone traps and gather insight to help connect the dots between midge forecasts and actual midge emergence in the spring (see it on Twitter #midgebusters).
The project collects field data from pheromone traps that attract male midges and the corresponding crop stage when emergence happens at around 65 site collection locations in fields across Alberta, Saskatchewan and Manitoba. The data is used to follow up on forecasting predictions to determine if wheat midge emergence aligns with the susceptible stage of the wheat to cause economic damage. “The pheromone traps and crop staging provide critical validation to compare with the soil core forecast and AAFC emergence maps to see what’s happening in real time,” says Wist.
Green isn’t always green
The midge forecast maps for 2022 were showing mostly green indicating low populations of overwintering cocoons collected from soil samples in fall 2021 – probably based on the exceptionally hot and dry summer in 2021. “So if you were a wheat grower, you might have looked at that and thought there isn’t much risk of wheat midge.”
And yet, that’s not really how things played out. Another reminder to Wist of the unpredictability of the midge. “The data we collected in 2022 has actually raised more questions than answers about wheat midge, with more midges caught in 2022 on average compared to 2021,” he says.
In 2022, in locations with adequate rainfall, they were finding male midges on traps in locations they wouldn’t have expected if they just relied on the forecast maps showing green or low risk.
“The forecasts are a great measure of what could happen, but not always a measure of what will happen,” says Wist. And 2022 up there was a lot of unexpected unpredictability with midge populations.”
For Wist, results from trapping and tracking wheat midge in 2022 showed how important it is to remain vigilant about the pest. “You can’t turn your back on wheat midge, even if the forecast says you’ll be okay. Why did we find midges when they weren’t in the soil sample? Well, that’s still a mystery.”
It’s all about the weather
When it comes to 2023, Wist can’t make any predictions. Midge populations are all weather dependant and he describes them as a ticking time bomb in the soil. “Wheat midge can last up to 13 years in the soil and still be viable.” There is much more to learn about this pest and Wist will be continuing the Midge Buster project to continue to gather valuable insights and hopes to gather more data about the number of female wheat midges found on wheat heads.
Best practices still the best approach
Wist reminds growers that planting midge tolerant wheat is the best agronomic practice against damage from the unpredictable pest. “If you don’t plant midge tolerant wheat, and the population reaches the economic threshold of one female per five heads of wheat, the yield loss starts at 15 per cent and goes up from there,” says Wist.
Growing midge tolerant wheat requires growers to sign a stewardship agreement to ensure the integrity of the technology – and ensures every bag contains a 10 per cent refuge on non-resistant seed to reduce the likelihood of wheat midge developing resistance to the Sm1 gene.
“The Sm1 gene is the only single resistant gene that’s used by breeders against wheat midge, and the only one available in wheat varieties in Canada,” he says.