Battling the bugs: Manitoba’s top 10 insect concerns of 2024
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Insects troubling to farmers haven’t changed much since 2024, but at St Jean Farm Days, Manitoba Agriculture entomologist John Gavloski shared which critters to watch for, which have made it back on the annual top 10 list and which one is no longer considered a top threat.
As someone who has monitored agricultural pests for decades, Gavloski provides invaluable insights to farmers, agronomists, and those working in agriculture.
“It’s a similar list to last year’s,” Gavloski noted. “The main difference is that Bertha armyworm made it back on the list, replacing diamondback moths, which weren’t as much of an issue this year.”
While some insect populations have declined, others have surged, demanding vigilance from Manitoba’s producers. Here’s a breakdown of the most concerning pests of 2024.
1. Grasshoppers: Persistent but manageable
Grasshoppers thrive in hot, dry conditions. While their numbers were lower in 2024 compared to 2023, some areas still required management.
“They overwinter as eggs and need some moisture to hatch,” Gavloski explained. “But they have to eat immediately to build up their fat reserves to become a nymph. If they don’t, they either starve or become more vulnerable to disease.”
Two-striped grasshoppers were the dominant species in last year’s surveys. “They’re general feeders, so keep an eye on them,” Gavloski advised. “Our August surveys showed good egg-laying conditions, so don’t be complacent.”
2. Cutworms: A cyclical challenge
Cutworms follow population cycles, peaking every few years before declining. “If you recall, 2019 and 2020 were bad cutworm years,” Gavloski said. “Since then, populations have been declining, but there were still cases of spraying in almost every agricultural region last year.”
Different cutworm species cause varying damage. “Dingy cutworms are tricky because they climb and feed at night,” Gavloski explained. “You’ll see defoliation, but no insects, because they burrow underground by day.” In contrast, redback cutworms sever plants at the base, leaving obvious damage.
Seed treatments can offer protection, but wet conditions can reduce their effectiveness. “These treatments are water-soluble, so if there’s heavy rain, they won’t last as long,” he warned.
3. Flea beetles: A chronic issue
Flea beetles continue to plague canola growers across Manitoba. “Almost every region saw spraying, and some fields had to be reseeded,” Gavloski said. “The issue last year was that cool temperatures slowed plant growth, prolonging the vulnerable seedling stage.”
He emphasized that if canola reaches the three- or four-leaf stage within three to four weeks, seed treatments usually provide adequate protection. “But if it takes longer, those treatments wear off, leaving plants exposed.”
4. Lygus bugs: A stealthy pest
Lygus bugs, which puncture plants with their needle-like beaks and suck out the juices, were a problem in some canola fields.
“In a dry year, they can be economically damaging because plants can’t compensate for the loss,” Gavloski explained. “The tricky part is they move fast. If you’re not using a sweep net, you might not even know they’re there.”
Threshold recommendations have changed. “We used to say 15 to 20 per sweep warranted spraying,” Gavloski said. “Now, it’s closer to 30. In dry years, 20 might be enough. Below 17, they might even be beneficial, stimulating more pod production.”
5. Diamondback moths: A false alarm in 2024
Diamondback moths are tracked annually using monitoring traps. “We had some high counts in June, especially in the Eastern and Interlake regions,” Gavloski said. “But nothing significant happened. Rainfall likely reduced their success.”
6. Cabbage Seedpod weevil: Expanding its range
Cabbage seedpod weevils aren’t yet an economic concern, but their range is expanding. “We first detected them in Manitoba in 2017,” Gavloski said. “This year, we found them just west of Morris, which is the furthest east we’ve seen them. However, their populations remain well below economic thresholds.”
7. Sunflower pests: midge and moth
Sunflower midge continued to cause edge damage in some fields, especially in the Eastern and Central regions. “There’s no spray for them, and they can create some nasty-looking heads,” Gavloski noted.
Sunflower moth larvae, which tunnel inside plants, also remained visible. “You can see their frass, those little piles of ground feces. But there’s no registered insecticide for them yet.”
8. Armyworms: A migration-dependent threat
Unlike many other pests, armyworms don’t overwinter in Manitoba. “They migrate intentionally, arriving in June and looking for dense grasses,” Gavloski said. “We had some infestations in the Central region and monitored them with traps.”
9. Aphids in small grains: Unpredictable but impactful
Aphids don’t overwinter in Manitoba either, making them difficult to predict. “They get blown in, so their impact varies each year,” Gavloski explained.
In 2024, English grain aphids were first spotted in late May, and oat-bird cherry aphids appeared in June. Some areas experienced high populations, prompting insecticide applications, particularly in oats and wheat in the Northwest and Eastern regions.
10. Bertha armyworm: Making a comeback
Bertha armyworm replaced diamondback moths on this year’s top 10 list. “It wasn’t an issue last year, but we saw more cases this year, particularly in canola,” Gavloski said.
Monitoring and management
Gavloski’s message to producers is clear: scouting remains the best defense against insect pests.
“Some of these insects come in cycles, some arrive unpredictably, and others are always around in low numbers,” he said. “Knowing what’s in your field, when they appear, and what their thresholds are can save you a lot of trouble – and money.”
Manitoba Agriculture’s monitoring programs, weekly pest updates, and ongoing research provide essential support to those on the frontlines of crop production. By staying informed and vigilant, farmers can minimize losses and ensure a successful growing season in the face of these persistent insect threats.