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There may be fewer wheat midge flying around fields this spring. According to the recently released annual forecast maps, there is a decreased risk of the pest that is known to cause yield and quality losses.

“The 2022 map is mostly green, which indicates midge levels of less than 600 per square metre. That’s good news for farmers,” says Dr. Tyler Wist, research scientist of field crop entomology with Agriculture and Agri-Food Canada in Saskatoon. Midge damage is still possible at this level, but risk is considerably reduced.

In past years, red pockets dotted the forecast maps, flagging areas of more than 1,800 midge per square metre, the most threatening level. In this year’s maps, only areas around Camrose Country, Alberta and the north-central region of Saskatchewan are shaded yellow and orange, which warns of potential for increased risk.

While the provincial maps are a good indicator for growers and agronomists of what’s to come, Mother Nature has the final say. Moisture – at least 25 mm of accumulative spring rainfall – ultimately determines the timing and severity of a midge infestation.

Keep scouting

Wist says that although the forecast for 2022 ‘looks rosy’ for growers, he clarifies that doesn’t mean they can forget about the pest. Wheat producers should assess risk based on their own field situation.

“The forecast maps are based on somebody’s field in your neighborhood – it’s not based on your individual field. If you’ve got low pockets in your fields, you might have a wheat midge problem that you don’t know about unless you go out and look for it. It’s important to keep scouting.”

Growers should plan to inspect fields for midge regularly as wheat heads emerge in late June and early July. Female midge lay eggs on the developing wheat heads. They are most active on warm, calm evenings and only live for four to five days, which makes scouting timing critical.

Heather Bird takes a soil core sample for the Alberta wheat midge forecast. Photo courtesy of Shelley Barkley, Alberta Agriculture and Forestry.

Getting a complete picture

Forecast maps are put together annually based on data from soil core surveys conducted in the fall. Samples are taken in wheat stubble and then analyzed back in the lab to determine the density of overwintering wheat midge cocoons. But now they’re just one piece of the puzzle for understanding midge populations.

A new annual initiative is helping to “ground truth” the forecast maps. Midge Busters is an in-season monitoring network developed by Wist and SeCan. It involves volunteers across the Prairies (SeCan members and staff as well as independent agronomists) using pheromone traps to count and report midge activity in real time during the growing season.

Wist is currently comparing the forecast maps with the Midge Busters reports. Preliminary results show that some of the hot spots on the 2021 maps did not lead to the expected midge pressure. Taking a closer look at weather data in these areas reinforces the role of moisture in midge infestations ­– there simply wasn’t enough to activate midge out of the ground.

More savings with midge tolerant varieties

While some growers look to forecasting to help manage wheat midge, others plan to plant midge tolerant wheat varieties regardless. These growers value the peace of mind and savings per acre in both time and money by not having to spray for the pest.

In 2010, research showed that growers saved $36 per acre when planting Midge Tolerant Wheat. Todd Hyra, SeCan Business Manager Western Canada, recently crunched the numbers based on 2021 data. “Using the same threshold damage of 15%, we calculated new savings to reflect current yield averages and wheat prices. Growers could now save $94.50 per acre when they use a Midge Tolerant Wheat variety,” he says. (This calculation is 15% x 70 bushels per acre x $9 per bushel.)

For Midge Tolerant Wheat growers who want to continue to realize this savings, following proper stewardship protocols is necessary to keep the technology viable for future. This means limiting the use of farm-saved seed to one generation past Certified. This practice maintains the interspersed refuge and prevents the build-up of a resistant midge population. Midge Tolerant Wheat also plays a role in reducing the overall midge population, which helps to keep the forecast maps green.

Tyler Wist’s summer students, Gabrielle Lee, Stean Kury and Michaela Merasty, take soil cores for wheat midge field assessments.

The 2021 forecast in Saskatchewan and Alberta called for wheat midge in abundance. But what the annual prediction couldn’t take into account is what Mother Nature had in store.

“Wheat midge is really tied to rain. Areas that received enough spring rain to kickstart development had wheat midge emergence and a really good correlation with the forecasting data,” says Dr. Tyler Wist, research scientist of field crop entomology with Agriculture and Agri-Food Canada in Saskatoon, SK.

Drought conditions throughout much of the Prairies, however, left much of the predicted midge population dormant in the soil. “If the rains don’t come, the midge doesn’t come up out of the ground,” says Wist.

A surprising development in some areas was a second flush of the pest later in the season. “Second flushes can sometimes happen after another big rain event,” he says. “It’s like some of them just don’t start developing until after a second hit of moisture. It’s a mechanism that we need to further explore.”

There is also work to be done to better monitor wheat midge emergence and essentially ‘ground truth’ the annual forecast maps.

“There is no coordinated monitoring of actual wheat midge emergence to know if the maps and models are giving good predictions,” says Wist. “With SeCan, I conceived of a network of pheromone traps in their member fields that would have the growers and their agronomists reporting in real time during the 2021 season.”

Pheromone traps were distributed to volunteers (seed growers, independent agronomists and SeCan staff) across the Prairies and the initiative was dubbed ‘Midge Busters.’

Midge Busters

The traps were placed in wheat fields and insect counts were done twice per week for one month. Participants entered their trap catches in an online platform so everyone could immediately see counts from other areas. Midge enthusiasts could follow along on Twitter under the #midgebuster hashtag.

“Ultimately, 67 fields were monitored with results showing midge in all traps with an average count of 50. Some traps had very low numbers, while others were as high as 1,350 midge per count,” reports Todd Hyra, SeCan Business Manager Western Canada. “The emergence rates will be correlated with rainfall data to help improve prediction models for the future.”

Hyra adds that the take-home message for many was the complexity of monitoring an insect that can come in multiple flushes. “It also reinforced the efficiency and convenience of growing Midge Tolerant Wheat as an effective and sustainable solution to a pest that has plagued growers for decades.”

What to expect for 2022

Should fields that expected high midge pressure in 2021 but missed a timely spring rain, be bracing for dormant midge to emerge in 2022?
Wist can’t say for certain. “We’ll know better when we see the forecast maps,” he says. Soon researchers will be heading into fields to collect soil samples that are the basis for these maps. “They pull the overwintering cocoons of the wheat midge out of the ground and open them up to see if they’ve been parasitized by Macroglenes penetrans,” explains Wist. The beneficial parasitoid helps to keep the midge population in check. “When a midge is parasitized it doesn’t go onto the map because it’s not viable.”

While growers await the maps, which are typically available in January, they can protect their wheat yields and quality by planning to seed Midge Tolerant Wheat and following stewardship protocols to keep the technology viable for future.

Wist says the Midge Busters initiative has given him a wealth of information that will help his team validate models and future predications. He is eager to build on the knowledge for next year. “Stay tuned for Midge Busters II in 2022,” he says.