Pests to watch in 2021

Friday, May 21, 2021

Each province has its own unique pest pressures, but some are proving to be universal problems across the Prairies.

by Taryn Milton

As growers in Western Canada prepare for the upcoming planting season, it's time to start thinking about what pests you might be dealing with this year.

From cutworms to flea beetles, grasshoppers to wheat stem sawfly, growers in Saskatchewan, Manitoba and Alberta saw a variety of pests in 2020 that can cause problems for this upcoming year.

While each province experiences different pest pressures each year, it's important to keep informed about what is happening in your area.

This month, Better Farming connects with entomologists in Saskatchewan and Manitoba and an insect survey technologist in Alberta to learn which pests caused problems last year and which ones might return.

We also review ways producers can keep an eye on what's happening as the 2021 season progresses.

Pests in Saskatchewan

In 2020, some growers had to deal with pea leaf weevil and cabbage seedpod weevil in low numbers, says Dr. James Tansey. He is the provincial entomologist at the Saskatchewan Ministry of Agriculture.

"Pea leaf weevil and cabbage seedpod weevil are invasive and they both found their way into Manitoba now, albeit at a relatively low level. They're working their way east and are working their way north from original points of invasion. So, they're getting around, but the numbers still seem to be low in the new areas of invasion," he tells Better Farming.

Diamondback moths had potential for greater concern last year for canola and mustard growers.

"We had big numbers in a few regions. We do pheromone trapping of these ones. We had early arrival of big numbers and I was getting to be a little concerned about the potential for economic damage, at least regionally with these pests," says Tansey.

Luckily, the high winds in 2020 helped reduce this pest's population for the next generation, says Tansey.

"We really didn't see what I feared would be a local boom in some of these diamondback moth populations. Sadly, some of these high winds also meant some sandblasting, in particular, seedling canola," he explains.

Canola growers also had to deal with flea beetles, both crucifer and striped.

"It seems, though, that the dominance of striped flea beetles, particularly in the northern parts of the province, continues. A shift in dominance between the striped flea beetle and the crucifer flea beetle was proposed about a dozen years ago, and it does seem to still be occurring," says Tansey.

"We had heavy populations in late summer of crucifer flea beetles. And so, in some cases, late-season crops were covered in large numbers of these pests."

Saskatchewan growers also had bertha armyworms to deal with in 2020, but in low numbers.

"We've seen the decline over the last three years of these pests. It is a cyclical pest, so it's subject to a number of different factors, not least of which are climate, pathogens, predators and parasitoids," says Tansey.

"An interesting thing about the bertha armyworm, is that it is a generalist. People usually think of it as being a canola pest, but it's actually become important for quinoa growers as well."

Quinoa growers also saw a number of pests become prevalent last season.

"There's Amauromyza, which is a stem-boring maggot and continues to be prevalent. There's also a weevil that's becoming important, particularly in the southeast or around the Indian Head, Sask. area. We have some reports of sweet potato aphid on this one as well," says Tansey.

"It seems that quinoa is on the menu for a number of different pests and a number of different animals are crossing over to feed on it."

Grasshoppers also caused some problems in 2020, including clearwing grasshoppers, reports Tansey.

Pests in Manitoba

Four main pests caused widespread damage in the province last year, says Dr. John Gavloski. He is the extension entomologist at Manitoba Agriculture and Resource Development.

"Flea beetles in canola, grasshoppers in lots of different crops, cutworms early in the season and also in lots of crops, and armyworms. Armyworms were more in the cereal grains and the forage grasses," he tells Better Farming.

"There were certainly other insects that were of concern, but they were more localized and didn't really result in a lot of control measures being needed. These four were the ones that were more widespread. So, they were the more serious pests for the year."

All four of these pests caused problems across the province with cutworms and flea beetles causing issues early in the season.

"With flea beetles, there are two things that can create a real big problem. One is the level of flea beetles, obviously, and the other is how long it's taking the canola to get from the time it's seeded until the three- to four-leaf stage. That's when it becomes a bit more resistant to the flea beetles," explains Gavloski.

Later in the season, grasshoppers and armyworms were the big concern for growers.

"Even in some of the fields, people were treating grasshoppers around the field edges in June or early July. The numbers were quite high in some areas," says Gavloski.

"Armyworms migrate in. They probably migrated in at some point in June, but in late June we were seeing the larvae getting to some of their larger stages. It was during those first few weeks in July that there was a lot of feeding damage."

Two other pests growers dealt with in smaller numbers last year were diamondback moths and pea aphids, says Gavloski.

Pests in Alberta

Growers here saw pests similar to the ones found in the other Prairie provinces. Bertha armyworms, grasshoppers, wheat midge and wheat stem sawfly were the four pests that caused problems, says Shelley Barkley. She is an insect survey technologist at Alberta Agriculture and Forestry.

"In the southeast corner, wheat stem sawfly is still causing some issues and in the southside of the county of Vulcan and the northside of Willow Creek. Other than that, producers were seeing the start of some bertha armyworm issues," she tells Better Farming.

"There were some reports coming in from the area around Highway 16, from Edmonton to the Saskatchewan border about wheat midge.

"Grasshoppers were also reported in Forty Mile County doing a lot of damage in lentils," Barkley says.

What to watch in 2021

Since some pests don't overwinter in Canada, not all pests prevalent last year are guaranteed to show up in 2021. But many do.

"Armyworms don't overwinter here. They migrate in and whether we get them and at what level, can vary greatly from year to year," says Gavloski.

"The other three main pest groups that I mentioned, they all overwinter here and given the right conditions, they can overwinter quite successfully. So, definitely cutworms, flea beetles and grasshoppers – those would be the top three priorities as far as things you need to scout for in 2021."

However, even the pests that do overwinter here may not come back in numbers as high as in previous years, says Tansey.

"There does seem to be a connection between these very cold snaps that we've been getting with not very much snow cover and reduced populations.

"So, these pests are not as cool-hardy as some others that have evolved in this climate. So once again, they are invasive, they are European initially and they're a little bit less cold-tolerant," he explains.

For 2021, it will be interesting to see the level at which the overwintering pests come back in since some areas received a lot of snow cover, says Tansey.

For Alberta, since it's an odd-numbered year, growers in the province could see the Bruner's spur-throated grasshopper, says Barkley.

"There has been evidence that the Bruner's spur-throated grasshopper has a two-year life cycle," she says. "The last time they were bad was in 2019, the time before that was 2017, and this particular species sort of lives north of Edmonton in the Peace Country."

Growers who had issues with the wheat stem sawfly last year may also want to consider using a solid-stem wheat variety this year to combat this pest, says Barkley.

Keep up-to-date

Since pest issues change from year to year, a good way to keep track of what's happening in your area is to follow the Prairie Pest Monitoring Network online at prairiepest.ca. The website covers all three provinces and the team sends a weekly email to subscribers, says Barkley.

Many grower groups also provide pest information and the Saskatchewan Ministry of Agriculture updates its website with important pests to watch, says Tansey.

Manitoba Agriculture and Resource Development provides a weekly Manitoba Crop Pest Update starting in May each year, says Gavloski.

"If there's anything that we see emerging as a threat, we make sure we get it into that update and we try to get that out to as many producers and agronomists as we can," he says.

The pest update works best if growers report pest observations to Gavloski and team so that this information can be shared with others in the area.

If growers see any new pests in 2021 that they have not seen before, all the experts recommend reaching out to them or an agronomist who can help identify the pest. BF